diff --git a/.depend b/.depend
index fe726b33da2b..15c292317e16 100644
--- a/.depend
+++ b/.depend
@@ -44,7 +44,8 @@ utils/clflags.cmx : \
     utils/clflags.cmi
 utils/clflags.cmi : \
     utils/profile.cmi \
-    utils/misc.cmi
+    utils/misc.cmi \
+    utils/config.cmi
 utils/compression.cmo : \
     utils/compression.cmi
 utils/compression.cmx : \
@@ -2304,6 +2305,7 @@ bytecomp/bytelibrarian.cmo : \
     utils/linkdeps.cmi \
     utils/format_doc.cmi \
     bytecomp/emitcode.cmi \
+    bytecomp/dll.cmi \
     utils/config.cmi \
     file_formats/cmo_format.cmi \
     utils/clflags.cmi \
@@ -2316,6 +2318,7 @@ bytecomp/bytelibrarian.cmx : \
     utils/linkdeps.cmx \
     utils/format_doc.cmx \
     bytecomp/emitcode.cmx \
+    bytecomp/dll.cmx \
     utils/config.cmx \
     file_formats/cmo_format.cmi \
     utils/clflags.cmx \
@@ -2430,14 +2433,17 @@ bytecomp/bytesections.cmi :
 bytecomp/dll.cmo : \
     utils/misc.cmi \
     utils/config.cmi \
+    file_formats/cmo_format.cmi \
     utils/binutils.cmi \
     bytecomp/dll.cmi
 bytecomp/dll.cmx : \
     utils/misc.cmx \
     utils/config.cmx \
+    file_formats/cmo_format.cmi \
     utils/binutils.cmx \
     bytecomp/dll.cmi
-bytecomp/dll.cmi :
+bytecomp/dll.cmi : \
+    file_formats/cmo_format.cmi
 bytecomp/emitcode.cmo : \
     parsing/unit_info.cmi \
     lambda/translmod.cmi \
@@ -5162,6 +5168,7 @@ middle_end/flambda/closure_conversion.cmo : \
     middle_end/flambda/flambda.cmi \
     lambda/debuginfo.cmi \
     middle_end/convert_primitives.cmi \
+    middle_end/compilenv.cmi \
     middle_end/compilation_unit.cmi \
     middle_end/flambda/base_types/closure_origin.cmi \
     middle_end/flambda/base_types/closure_id.cmi \
@@ -5190,6 +5197,7 @@ middle_end/flambda/closure_conversion.cmx : \
     middle_end/flambda/flambda.cmx \
     lambda/debuginfo.cmx \
     middle_end/convert_primitives.cmx \
+    middle_end/compilenv.cmx \
     middle_end/compilation_unit.cmx \
     middle_end/flambda/base_types/closure_origin.cmx \
     middle_end/flambda/base_types/closure_id.cmx \
@@ -7886,6 +7894,17 @@ lex/table.cmo : \
 lex/table.cmx : \
     lex/table.cmi
 lex/table.cmi :
+tools/byterntm.cmo : \
+    utils/misc.cmi \
+    bytecomp/bytesections.cmi \
+    tools/byterntm.cmi
+tools/byterntm.cmx : \
+    utils/misc.cmx \
+    bytecomp/bytesections.cmx \
+    tools/byterntm.cmi
+tools/byterntm.cmi : \
+    utils/misc.cmi \
+    bytecomp/bytesections.cmi
 tools/cmpbyt.cmo : \
     bytecomp/bytesections.cmi \
     tools/cmpbyt.cmi
@@ -7981,6 +8000,9 @@ tools/objinfo.cmo : \
     typing/ident.cmi \
     utils/format_doc.cmi \
     middle_end/flambda/export_info.cmi \
+    bytecomp/dll.cmi \
+    utils/config.cmi \
+    middle_end/compilenv.cmi \
     middle_end/compilation_unit.cmi \
     file_formats/cmxs_format.cmi \
     file_formats/cmx_format.cmi \
@@ -7988,6 +8010,7 @@ tools/objinfo.cmo : \
     file_formats/cmo_format.cmi \
     file_formats/cmi_format.cmi \
     bytecomp/bytesections.cmi \
+    tools/byterntm.cmi \
     utils/binutils.cmi \
     tools/objinfo.cmi
 tools/objinfo.cmx : \
@@ -8004,6 +8027,9 @@ tools/objinfo.cmx : \
     typing/ident.cmx \
     utils/format_doc.cmx \
     middle_end/flambda/export_info.cmx \
+    bytecomp/dll.cmx \
+    utils/config.cmx \
+    middle_end/compilenv.cmx \
     middle_end/compilation_unit.cmx \
     file_formats/cmxs_format.cmi \
     file_formats/cmx_format.cmi \
@@ -8011,6 +8037,7 @@ tools/objinfo.cmx : \
     file_formats/cmo_format.cmi \
     file_formats/cmi_format.cmx \
     bytecomp/bytesections.cmx \
+    tools/byterntm.cmx \
     utils/binutils.cmx \
     tools/objinfo.cmi
 tools/objinfo.cmi :
@@ -10375,9 +10402,11 @@ testsuite/lib/testing.cmx : \
 testsuite/lib/testing.cmi :
 testsuite/tools/cmdline.cmo : \
     testsuite/tools/harness.cmi \
+    utils/config.cmi \
     testsuite/tools/cmdline.cmi
 testsuite/tools/cmdline.cmx : \
     testsuite/tools/harness.cmx \
+    utils/config.cmx \
     testsuite/tools/cmdline.cmi
 testsuite/tools/cmdline.cmi : \
     testsuite/tools/harness.cmi
@@ -10413,6 +10442,7 @@ testsuite/tools/environment.cmo : \
     file_formats/cmt_format.cmi \
     file_formats/cmo_format.cmi \
     bytecomp/bytesections.cmi \
+    tools/byterntm.cmi \
     testsuite/tools/environment.cmi
 testsuite/tools/environment.cmx : \
     otherlibs/unix/unix.cmx \
@@ -10423,6 +10453,7 @@ testsuite/tools/environment.cmx : \
     file_formats/cmt_format.cmx \
     file_formats/cmo_format.cmi \
     bytecomp/bytesections.cmx \
+    tools/byterntm.cmx \
     testsuite/tools/environment.cmi
 testsuite/tools/environment.cmi : \
     testsuite/tools/harness.cmi
@@ -10466,13 +10497,20 @@ testsuite/tools/expect.cmi : \
     parsing/location.cmi
 testsuite/tools/harness.cmo : \
     otherlibs/unix/unix.cmi \
+    utils/misc.cmi \
     utils/config.cmi \
+    tools/byterntm.cmi \
     testsuite/tools/harness.cmi
 testsuite/tools/harness.cmx : \
     otherlibs/unix/unix.cmx \
+    utils/misc.cmx \
     utils/config.cmx \
+    tools/byterntm.cmx \
     testsuite/tools/harness.cmi
-testsuite/tools/harness.cmi :
+testsuite/tools/harness.cmi : \
+    utils/misc.cmi \
+    utils/config.cmi \
+    tools/byterntm.cmi
 testsuite/tools/lexcmm.cmo : \
     testsuite/tools/parsecmm.cmi \
     utils/misc.cmi \
@@ -10531,12 +10569,14 @@ testsuite/tools/parsecmmaux.cmi : \
     middle_end/backend_var.cmi
 testsuite/tools/testBytecodeBinaries.cmo : \
     otherlibs/unix/unix.cmi \
+    utils/misc.cmi \
     testsuite/tools/harness.cmi \
     testsuite/tools/environment.cmi \
     utils/config.cmi \
     testsuite/tools/testBytecodeBinaries.cmi
 testsuite/tools/testBytecodeBinaries.cmx : \
     otherlibs/unix/unix.cmx \
+    utils/misc.cmx \
     testsuite/tools/harness.cmx \
     testsuite/tools/environment.cmx \
     utils/config.cmx \
@@ -10580,6 +10620,7 @@ testsuite/tools/testRelocation.cmo : \
     testsuite/tools/harness.cmi \
     testsuite/tools/environment.cmi \
     utils/config.cmi \
+    bytecomp/bytelink.cmi \
     testsuite/tools/testRelocation.cmi
 testsuite/tools/testRelocation.cmx : \
     otherlibs/unix/unix.cmx \
@@ -10587,6 +10628,7 @@ testsuite/tools/testRelocation.cmx : \
     testsuite/tools/harness.cmx \
     testsuite/tools/environment.cmx \
     utils/config.cmx \
+    bytecomp/bytelink.cmx \
     testsuite/tools/testRelocation.cmi
 testsuite/tools/testRelocation.cmi : \
     testsuite/tools/harness.cmi \
@@ -10640,11 +10682,13 @@ testsuite/tools/test_in_prefix.cmx : \
     testsuite/tools/test_in_prefix.cmi
 testsuite/tools/test_in_prefix.cmi :
 testsuite/tools/test_ld_conf.cmo : \
+    otherlibs/unix/unix.cmi \
     testsuite/tools/harness.cmi \
     testsuite/tools/environment.cmi \
     utils/config.cmi \
     testsuite/tools/test_ld_conf.cmi
 testsuite/tools/test_ld_conf.cmx : \
+    otherlibs/unix/unix.cmx \
     testsuite/tools/harness.cmx \
     testsuite/tools/environment.cmx \
     utils/config.cmx \
diff --git a/.gitattributes b/.gitattributes
index 1069ce73e3d7..de6bb51ad890 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -41,6 +41,21 @@
 # the lines involved in the conflict, which is arguably worse
 #/Changes                 merge=union
 
+testsuite/Makefile       export-subst
+
+# Files and directories excluded from git-generated tarballs.
+.github                  export-ignore
+manual                   export-ignore
+release-info             export-ignore
+testsuite/tests          export-ignore
+tools/ci                 export-ignore
+.gitattributes           export-ignore
+.gitignore               export-ignore
+.gitmodules              export-ignore
+.mailmap                 export-ignore
+ocaml-variants.install   export-ignore
+ocaml-variants.opam      export-ignore
+
 # No header for text and META files (would be too obtrusive).
 *.md                     typo.missing-header
 README*                  typo.missing-header
diff --git a/.github/workflows/build-msvc.yml b/.github/workflows/build-msvc.yml
index fb78b02a21bb..cb96bacc5749 100644
--- a/.github/workflows/build-msvc.yml
+++ b/.github/workflows/build-msvc.yml
@@ -33,10 +33,13 @@ jobs:
         with:
           script: |
             // # Always test cl and clang-cl
-            let compilers = ['cl', 'clang-cl'];
+            let compilers = ['clang-cl'];
             // # Also test i686 MSVC
             let include = [
-              {cc: 'cl', arch: 'i686'}];
+              {os: 'windows-latest', cc: 'cl', arch: 'i686', opam: 'false', prefix: '$PROGRAMFILES/Бактріан🐫', libdir: 'relative'},
+              {os: 'windows-2025', cc: 'cl', arch: 'x86_64', opam: 'true', prefix: 'C:\\\\Бактріан🐫'},
+              {os: 'windows-2025', cc: 'cl', arch: 'i686', opam: 'true', prefix: 'C:\\\\Бактріан🐫'}];
+            let libdir = ['absolute'];
             // # If this is a pull request, see if the PR has the
             // # 'CI: Full matrix' label. This is done using an API request,
             // # rather than from context.payload.pull_request.labels, since we
@@ -52,10 +55,14 @@ jobs:
                 // # Test Cygwin as well
                 compilers.push('gcc');
                 // # Test bytecode-only Cygwin
-                include.push({cc: 'gcc', arch: 'x86_64', config_arg: '--disable-native-toplevel --disable-native-compiler'});
+                include.push({os: 'windows-latest', prefix: '$PROGRAMFILES/Бактріан🐫', opam: ['false'], cc: 'gcc', arch: 'x86_64', libdir: 'absolute', config_arg: '--disable-native-toplevel --disable-native-compiler'});
+                // # Test i686 MSVC absolute
+                include.push({os: 'windows-latest', prefix: '$PROGRAMFILES/Бактріан🐫', opam: ['false'], cc: 'cl', arch: 'i686', libdir: 'absolute'});
+                // # Expand the main matrix to include relative testing
+                libdir.push('relative');
               }
             }
-            return {config_arg: [''], arch: ['x86_64'], cc: compilers, include: include};
+            return {os: ['windows-latest'], prefix: ['$PROGRAMFILES/Бактріан🐫'], opam: ['false'], config_arg: [''], arch: ['x86_64'], cc: compilers, libdir: libdir, include: include};
       - name: Determine if the testsuite should be skipped
         id: skip
         uses: actions/github-script@v7
@@ -73,13 +80,13 @@ jobs:
   build:
     permissions: {}
 
-    runs-on: windows-latest
+    runs-on: ${{ matrix.os }}
 
     needs: config
 
     timeout-minutes: ${{ matrix.cc == 'gcc' && 90 || 60 }}
 
-    name: ${{ matrix.cc == 'cl' && 'MSVC' || matrix.cc == 'gcc' && 'Cygwin' || 'clang-cl' }} ${{ matrix.arch }} ${{ matrix.config_arg != '' && format('({0})', matrix.config_arg) || '' }}
+    name: ${{ matrix.cc == 'cl' && 'MSVC' || matrix.cc == 'gcc' && 'Cygwin' || 'clang-cl' }} ${{ matrix.arch }} ${{ matrix.libdir }} ${{ matrix.config_arg != '' && format('({0})', matrix.config_arg) || '' }}
 
     strategy:
       matrix: ${{ fromJSON(needs.config.outputs.matrix) }}
@@ -102,7 +109,7 @@ jobs:
       - name: Install Cygwin
         uses: cygwin/cygwin-install-action@v3
         with:
-          packages: make,${{ matrix.cc != 'gcc' && 'mingw64-x86_64-' || 'gcc-fortran,' }}gcc-core
+          packages: make,${{ matrix.cc != 'gcc' && 'mingw64-x86_64-' || 'gcc-fortran,' }}gcc-core,rsync,unzip
           install-dir: 'D:\cygwin'
 
       - name: Save Cygwin cache
@@ -118,6 +125,13 @@ jobs:
           arch: ${{ matrix.arch == 'x86_64' && 'x64' || 'x86' }}
         if: matrix.cc != 'gcc'
 
+      - name: Install opam
+        if: matrix.opam == 'true'
+        shell: pwsh
+        run: |
+          winget install opam --accept-source-agreements
+          Add-Content -Path $env:GITHUB_PATH -Value "$env:LOCALAPPDATA\Microsoft\WinGet\Links"
+
       - name: Compute a key to cache configure results
         id: autoconf-cache-key
         env:
@@ -136,11 +150,14 @@ jobs:
         env:
           CONFIG_ARGS: >-
             --cache-file=config.cache
-            --prefix "${{ matrix.cc != 'gcc' && '$PROGRAMFILES/Бактріан🐫' || '$(cygpath "$PROGRAMFILES/Бактріан🐫")'}}"
+            --prefix ${{ matrix.cc != 'gcc' && format('"{0}/_opam"', matrix.prefix) || format('"$(cygpath "{0}")"', matrix.prefix) }}
+            --docdir ${{ format((matrix.cc != 'gcc' && '"{0}/_opam/doc/ocaml"' || '"$(cygpath "{0}/doc/ocaml")"'), matrix.prefix) }}
             ${{ matrix.cc != 'gcc' && format('--host={0}-pc-windows', matrix.arch) || '' }}
             ${{ matrix.cc != 'gcc' && format('CC={0}', matrix.cc) || '' }}
             --enable-ocamltest
             ${{ endsWith(matrix.arch, '64') && '--enable-native-toplevel' || '--disable-native-toplevel' }}
+            ${{ matrix.libdir == 'relative' && '--with-relative-libdir' || '--without-relative-libdir' }}
+            ${{ matrix.libdir == 'relative' && '--enable-runtime-search --enable-runtime-search-target=fallback' || '--disable-runtime-search --disable-runtime-search-target' }}
             ${{ matrix.config_arg }}
         run: |
           eval $(tools/msvs-promote-path)
@@ -193,8 +210,25 @@ jobs:
           make tests
 
       - name: Install the compiler
+        if: matrix.opam != 'true'
         run: make install
 
+      - name: Create opam switch
+        if: matrix.opam == 'true'
+        env:
+          OPAMSWITCH: ${{ matrix.prefix }}
+        run: |
+          make OPAM_PACKAGE_NAME=ocaml-variants INSTALL_MODE=opam install
+          opam init --cli=2.4 --bare --yes --disable-sandboxing --auto-setup --cygwin-local-install
+          # These commands intentionally run using opam's "default" CLI
+          opam switch create '${{ env.OPAMSWITCH }}' --empty
+          opam pin add --no-action --kind=path ocaml-variants .
+          opam pin add --no-action flexdll flexdll
+          opam pin add --no-action winpthreads winpthreads
+          opam install --yes flexdll winpthreads
+          opam install --yes --assume-built ocaml-variants
+          opam exec -- ocamlc -v
+
       - name: Test in prefix
         run: |
           eval $(tools/msvs-promote-path)
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 0eb47cf80be8..a6f30541663e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -59,7 +59,7 @@ jobs:
          '${{ github.event.repository.full_name }}'
       - name: Configure tree
         run: |
-          MAKE_ARG=-j CONFIG_ARG='--enable-flambda --enable-cmm-invariants --enable-dependency-generation --enable-native-toplevel' OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh configure
+          MAKE_ARG=-j CONFIG_ARG='--enable-flambda --enable-cmm-invariants --enable-dependency-generation --enable-native-toplevel --with-relative-libdir --enable-runtime-search --enable-runtime-search-target=fallback' OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh configure
       - name: Build
         run: |
           MAKE_ARG=-j bash -xe tools/ci/actions/runner.sh build
@@ -78,6 +78,7 @@ jobs:
 #        debug runtime and minor heap verification.
 # debug-s4096: select testsuite run with the debug runtime and a small
 #              minor heap.
+# opam: constructs an opam local switch from the compiler.
   normal:
     name: ${{ matrix.name }}
     needs: [build, config]
@@ -88,6 +89,8 @@ jobs:
           - id: normal
             name: normal
             dependencies: texlive-latex-extra texlive-fonts-recommended texlive-luatex hevea sass
+          - id: opam
+            name: opam installation
           - id: debug
             name: extra (debug)
           - id: debug-s4096
@@ -134,11 +137,19 @@ jobs:
       - name: Install
         if: matrix.id == 'normal'
         run: |
-         MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh install
+          MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh install
+      - name: Create opam switch
+        if: matrix.id == 'opam'
+        run: |
+          MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh opam
       - name: Test in prefix
-        if: matrix.id == 'normal'
+        if: matrix.id == 'normal' || matrix.id == 'opam'
         run: |
-         MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh test-in-prefix
+          MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh test-in-prefix
+      - name: Test in prefix (alternate configuration)
+        if: matrix.id == 'normal' && needs.config.outputs.full-matrix == 'true'
+        run: |
+          MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh re-test-in-prefix
       - name: Build the manual
         if: matrix.id == 'normal' && needs.build.outputs.manual_changed == 'true'
         run: |
@@ -152,9 +163,23 @@ jobs:
   config:
     runs-on: ubuntu-latest
     outputs:
+      full-matrix: ${{ steps.full.outputs.result }}
       jobs: ${{ steps.jobs.outputs.result }}
       skip-testsuite: ${{ steps.skip.outputs.result }}
     steps:
+      - name: Record if the build matrix is expanded
+        id: full
+        uses: actions/github-script@v7
+        with:
+          script: |
+            let full_matrix = false;
+            if (context.payload.pull_request) {
+              const { data: labels } =
+                await github.rest.issues.listLabelsOnIssue({...context.repo, issue_number: context.payload.pull_request.number});
+              full_matrix = labels.some(label => label.name === 'CI: Full matrix');
+            }
+            console.log('Full matrix: ' + full_matrix);
+            return full_matrix;
       - name: Compute matrix for the "others" job
         id: jobs
         uses: actions/github-script@v7
@@ -165,10 +190,12 @@ jobs:
               {name: 'linux-O0', os: 'ubuntu-latest',
                config_arg: "CFLAGS='-O0'"},
               {name: 'linux-arm64', os: 'ubuntu-24.04-arm',
+               config_arg: '--with-target-sh=exe --enable-runtime-search-target=fallback',
                'test-in-prefix': true},
               {name: 'macos-x86_64', os: 'macos-15-intel',
                'test-in-prefix': true},
               {name: 'macos-arm64', os: 'macos-latest',
+               config_arg: '--with-relative-libdir --enable-runtime-search',
                'test-in-prefix': true}];
             // # If this is a pull request, see if the PR has the
             // # 'CI: Full matrix' label. This is done using an API request,
@@ -182,13 +209,16 @@ jobs:
                 await github.rest.issues.listLabelsOnIssue({...context.repo, issue_number: context.payload.pull_request.number});
               if (labels.some(label => label.name === 'CI: Full matrix')) {
                 console.log('Full matrix requested');
-                // # Add "static" and "minimal" jobs
+                // # Add "static", "minimal" and "unsuffixed" jobs
                 jobs = jobs.concat([
                   {name: 'static', os: 'ubuntu-latest',
                    config_arg: '--disable-native-toplevel --disable-shared',
                    'test-in-prefix': true},
                   {name: 'minimal', os: 'ubuntu-latest',
-                   config_arg: '--disable-native-toplevel --disable-native-compiler --disable-shared --disable-debug-runtime --disable-instrumented-runtime --disable-systhreads --disable-str-lib --disable-unix-lib --disable-ocamldoc'}]);
+                   config_arg: '--disable-native-toplevel --disable-native-compiler --disable-shared --disable-debug-runtime --disable-instrumented-runtime --disable-systhreads --disable-str-lib --disable-unix-lib --disable-ocamldoc'},
+                  {name: 'unsuffixed', os: 'ubuntu-latest',
+                   config_arg: '--disable-suffixing',
+                   'test-in-prefix': true}]);
               }
             }
             return jobs;
@@ -250,6 +280,10 @@ jobs:
         if: ${{ matrix.test-in-prefix }}
         run: |
           MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh test-in-prefix
+      - name: Test in prefix (alternate configuration)
+        if: ${{ matrix.test-in-prefix && needs.config.outputs.full-matrix == 'true' && !contains(matrix.config_arg, '--disable-suffixing') }}
+        run: |
+          MAKE_ARG=-j OCAMLRUNPARAM=b,v=0 bash -xe tools/ci/actions/runner.sh re-test-in-prefix
 
   i386:
     runs-on: ubuntu-latest
@@ -282,4 +316,8 @@ jobs:
           su ocaml -c "bash -xe tools/ci/actions/runner.sh install"
       - name: Test in prefix
         run: |
-          su ocaml -c "bash -xe tools/ci/actions/runner.sh test-in-prefix"
+          MAKE_ARG=-j su ocaml -c "bash -xe tools/ci/actions/runner.sh test-in-prefix"
+      - name: Test in prefix (alternate configuration)
+        if: ${{ needs.config.outputs.full-matrix == 'true' }}
+        run: |
+          MAKE_ARG=-j su ocaml -c "bash -xe tools/ci/actions/runner.sh re-test-in-prefix"
diff --git a/.gitignore b/.gitignore
index 4159c2a270b7..c3d7e7a5102a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,6 +26,7 @@
 *.cmx[as]
 *.cmti
 *.annot
+*.stripped
 *.exe
 *.exe.manifest
 .DS_Store
@@ -240,6 +241,7 @@ META
 /runtime/primitives
 /runtime/primitives*.new
 /runtime/prims.c
+/runtime/sys_int.h
 /runtime/caml/exec.h
 /runtime/caml/opnames.h
 /runtime/caml/version.h
@@ -251,13 +253,10 @@ META
 /runtime/build_config.h
 /runtime/sak
 
-/stdlib/runtime.info
 /stdlib/runtime-launch-info
 /stdlib/labelled-*
 /stdlib/caml
 /stdlib/sys.ml
-/stdlib/target_runtime.info
-/stdlib/target_runtime-launch-info
 
 /testsuite/**/*.result
 /testsuite/**/*.opt_result
@@ -272,6 +271,7 @@ META
 
 /testsuite/tools/codegen
 /testsuite/tools/dump_load_path
+/testsuite/tools/poisonedruntime
 /testsuite/tools/expect
 /testsuite/tools/lexcmm.ml
 /testsuite/tools/parsecmm.ml
@@ -281,6 +281,7 @@ META
 /testsuite/tools/test_in_prefix.opt
 /testsuite/tools/toolchain.ml
 
+/tools/byterntm.ml
 /tools/ocamldep
 /tools/ocamldep.opt
 /tools/ocamlprof
diff --git a/Changes b/Changes
index 486c5313a290..271adfa7c4e0 100644
--- a/Changes
+++ b/Changes
@@ -1,14 +1,111 @@
 OCaml 5.3 maintenance version
 -----------------------------
 
-- #14007, #14015: Fix memory corruption when an exception is raised during
-  demarshaling.
-  (Benoît Vaugon, review by David Allsopp and Gabriel Scherer)
+### Runtime system:
+
+* #14243: Explicit relative paths in ld.conf (".", "..", "./<path...>",
+  "../<path...>") are interpreted as being relative to the directory ld.conf
+  was loaded from, and the default ld.conf now uses relative paths, rather than
+  embedding the absolute path to the Standard Library. The brave may continue to
+  put implicit paths in ld.conf. The interpretation of CAML_LD_LIBRARY_PATH is
+  unaltered. Additionally, ld.conf is loaded from all of $OCAMLLIB/ld.conf,
+  $CAMLLIB/ld.conf and standard_library_default/ld.conf rather than just the
+  first one found. ld.conf files with CRLF line endings are now consistently
+  normalised on both Windows and Unix.
+  (David Allsopp, review by Jonah Beckford, Damien Doligez and Hugo Heuzard)
+
+- #14244, #14802, #14846: Added --with-relative-libdir which allows the runtime
+  and the compilers to locate the Standard Library relative to where the
+  binaries themselves are installed, removing the absolute path previously
+  embedded in caml_standard_library_default. Executables linked with
+  `ocamlc -custom` now always attempt to load bytecode from the executable
+  itself, rather than first trying `argv[0]`.
+  (David Allsopp, review by Jonah Beckford, Antonin Décimo, Damien Doligez,
+   Samuel Hym and Vincent Laviron)
+
+- #14245: Introduce Runtime IDs for use in filename mangling to allow different
+  configurations and different versions of the runtime system to coexist
+  harmoniously on a single system. The IDs are used, along with the host
+  triplet, to provide mangled names for the ocamlrun executable and its variants
+  and the DLL versions of both the bytecode and native runtimes, with symlinks
+  created for the original names. They are also used to mangle the names of stub
+  libraries so that stub libraries compiled for a given configuration of the
+  runtime will only be sought by that runtime. The behaviour is disabled by
+  configuring with --disable-suffixing.
+  (David Allsopp, review by Damien Doligez and Samuel Hym)
+
+### Tools:
+
+- #14245: ocamlobjinfo now displays the runtime invoked by a bytecode
+  executable (either from the RNTM section or by analysing the shebang lines)
+  (David Allsopp, review by Damien Doligez and Samuel Hym)
+
+### Compiler user-interface and warnings:
+
+- #14244: Add -set-runtime-default option to the compiler, allowing the default
+  value of the Standard Library location used by the runtime to be overridden.
+  (Antonin Décimo, review by David Allsopp, Jonah Beckford, Damien Doligez and
+   Samuel Hym)
+
+- #14245: New option -launch-method for ocamlc allows the method used by a
+  tendered bytecode executable to locate the interpreter to be given explicitly.
+  In particular, it makes it easier to specify the use of the executable
+  launcher on Unix. New option -runtime-search extends the bytecode executable
+  header to be able to search for the runtime interpreter in the directory
+  containing the executable and in PATH rather than relying on a single
+  hard-coded path.
+  (David Allsopp, review by Damien Doligez and Samuel Hym)
+
+### Internal/compiler-libs changes:
+
+- #14243: ocamlc now uses the same code as the runtime to parse ld.conf (via a
+  C primitive), eliminating some highly obscure corner cases.
+  (David Allsopp, review by Jonah Beckford, Damien Doligez and Hugo Heuzard)
+
+### Build system:
+
+- #13494: Use native symlinks on Windows for the OCaml installation, reducing
+  disk usage considerably.
+  (David Allsopp, review by Nicolás Ojeda Bär and Gabriel Scherer)
+
+- #13789: Harden the escaping of backslashes when generating
+  runtime/build_config.h (in particular, if the underlying implementation of sh
+  is dash, rather than bash, this now works correctly).
+  (David Allsopp and Samuel Hym, review by Antonin Décimo and Gabriel Scherer)
+
+- #14243: New configure option --with-additional-stublibsdir allows an
+  additional directory to be added to the start of ld.conf. Additionally, the
+  stublibs subdirectory is no longer created, nor added to ld.conf, when
+  building OCaml with --disable-shared.
+  (David Allsopp, review by Jonah Beckford, Damien Doligez and Hugo Heuzard)
+
+- #14244: When targeting native Windows on Cygwin or MSYS2, preserve
+  backslashes in the supplied `--prefix` (in particular, backslashes instead of
+  slashes will then be displayed by `ocamlopt -config-var standard_library`).
+  If the supplied prefix contains a slash, then it is normalised, as
+  previously.
+  (David Allsopp, review by Jonah Beckford, Antonin Décimo, Damien Doligez and
+   Samuel Hym)
+
+- #14245: New --enable-runtime-search configure option controls the
+  -runtime-search option used to build the bytecode binaries in the compiler
+  distribution. --enable-runtime-search-target controls the default value of
+  -runtime-search used for bytecode executables produced by the compiler.
+  (David Allsopp, review by Damien Doligez and Samuel Hym)
+
+### Bug fixes:
 
 - #13790: Fix bytecode-only build of Cygwin when flexlink is being bootstrapped
   with the compiler.
   (David Allsopp, review by Antonin Décimo and Miod Vallat)
 
+- #14007, #14015: Fix memory corruption when an exception is raised during
+  demarshaling.
+  (Benoît Vaugon, review by David Allsopp and Gabriel Scherer)
+
+- #14871, #14914: Ignore OCAMLTOP_INCLUDE_PATH during the build.
+  (David Allsopp, report by Andreas Rossberg, review by Florian Angeletti)
+
 OCaml 5.3.0 (8 January 2025)
 ----------------------------
 
diff --git a/Makefile b/Makefile
index 02e6f79e7e99..2b89f31f5c2f 100644
--- a/Makefile
+++ b/Makefile
@@ -16,6 +16,8 @@
 # The main Makefile
 
 ROOTDIR = .
+SUBDIR_NAME =
+
 # NOTE: it is important that the OCAMLDEP and OCAMLLEX variables
 # are defined *before* Makefile.common gets included, so that
 # their local definitions here take precedence over their
@@ -52,8 +54,6 @@ PERVASIVES=$(STDLIB_MODULES) outcometree topprinters topdirs toploop
 
 LIBFILES=stdlib.cma std_exit.cmo *.cmi $(HEADER_NAME)
 
-COMPLIBDIR=$(LIBDIR)/compiler-libs
-
 TOPINCLUDES=$(addprefix -I otherlibs/,$(filter-out %threads,$(OTHERLIBRARIES)))
 
 expunge := expunge$(EXE)
@@ -482,9 +482,11 @@ utils/config_boot.ml: utils/config.fixed.ml utils/config.common.ml
 utils/config_main.ml: utils/config.generated.ml utils/config.common.ml
 	$(V_GEN)cat $^ > $@
 
+ADDITIONAL_CONFIGURE_ARGS ?=
 .PHONY: reconfigure
 reconfigure:
-	ac_read_git_config=true ./configure $(CONFIGURE_ARGS)
+	ac_read_git_config=true ./configure $(CONFIGURE_ARGS) \
+	                                    $(ADDITIONAL_CONFIGURE_ARGS)
 
 utils/domainstate.ml: utils/domainstate.ml.c runtime/caml/domain_state.tbl
 	$(V_GEN)$(CPP) -I runtime/caml $< > $@
@@ -641,12 +643,16 @@ flexlink.byte$(EXE): $(FLEXDLL_SOURCES)
 	rm -f $(FLEXDLL_SOURCE_DIR)/flexlink.exe
 	$(MAKE) -C $(FLEXDLL_SOURCE_DIR) $(FLEXLINK_BUILD_ENV) \
 	  OCAMLRUN='$$(ROOTDIR)/boot/ocamlrun$(EXE)' NATDYNLINK=false \
-	  OCAMLOPT='$(value BOOT_OCAMLC) $(USE_RUNTIME_PRIMS) $(USE_STDLIB)' \
+	  OCAMLOPT=$(call QUOTE_SINGLE,$(value BOOT_OCAMLC) \
+	                                 $(USE_RUNTIME_PRIMS) \
+	                                 $(BYTECODE_LAUNCHER_FLAGS) \
+	                                 $(USE_STDLIB)) \
 	  flexlink.exe support
 	cp $(FLEXDLL_SOURCE_DIR)/flexlink.exe $@
+	cp $(addprefix $(FLEXDLL_SOURCE_DIR)/, $(FLEXDLL_OBJECTS)) $(ROOTDIR)
 
 partialclean::
-	rm -f flexlink.byte flexlink.byte.exe
+	rm -f flexlink.byte flexlink.byte.exe flexdll_*.o flexdll_*.obj
 
 $(BYTE_BINDIR)/flexlink$(EXE): \
     boot/ocamlrun$(EXE) flexlink.byte$(EXE) | $(BYTE_BINDIR)
@@ -654,7 +660,6 @@ $(BYTE_BINDIR)/flexlink$(EXE): \
 # Start with a copy to ensure that the result is always executable
 	cp boot/ocamlrun$(EXE) $@
 	cat flexlink.byte$(EXE) >> $@
-	cp $(addprefix $(FLEXDLL_SOURCE_DIR)/, $(FLEXDLL_OBJECTS)) $(BYTE_BINDIR)
 
 partialclean::
 	rm -f $(BYTE_BINDIR)/flexlink $(BYTE_BINDIR)/flexlink.exe
@@ -716,9 +721,9 @@ compare:
 # The core system has to be rebuilt after bootstrap anyway, so strip ocamlc
 # and ocamllex, which means the artefacts should be identical.
 	mv ocamlc$(EXE) ocamlc.tmp
-	$(OCAMLRUN) tools/stripdebug -all ocamlc.tmp ocamlc$(EXE)
+	$(OCAMLRUN) tools/stripdebug$(EXE) -all ocamlc.tmp ocamlc$(EXE)
 	mv lex/ocamllex$(EXE) ocamllex.tmp
-	$(OCAMLRUN) tools/stripdebug -all ocamllex.tmp lex/ocamllex$(EXE)
+	$(OCAMLRUN) tools/stripdebug$(EXE) -all ocamllex.tmp lex/ocamllex$(EXE)
 	rm -f ocamllex.tmp ocamlc.tmp
 	@if $(CMPCMD) boot/ocamlc ocamlc$(EXE) \
          && $(CMPCMD) boot/ocamllex lex/ocamllex$(EXE); \
@@ -746,7 +751,7 @@ promote-cross: promote-common
 # Promote the newly compiled system to the rank of bootstrap compiler
 # (Runs on the new runtime, produces code for the new runtime)
 .PHONY: promote
-promote: PROMOTE = $(OCAMLRUN) tools/stripdebug -all
+promote: PROMOTE = $(OCAMLRUN) tools/stripdebug$(EXE) -all
 promote: promote-common
 	rm -f boot/ocamlrun$(EXE)
 	cp runtime/ocamlrun$(EXE) boot/ocamlrun$(EXE)
@@ -881,11 +886,11 @@ flexlink.opt$(EXE): \
     $(FLEXDLL_SOURCES) | $(BYTE_BINDIR)/flexlink$(EXE) $(OPT_BINDIR)
 	rm -f $(FLEXDLL_SOURCE_DIR)/flexlink.exe
 	$(MAKE) -C $(FLEXDLL_SOURCE_DIR) $(FLEXLINK_BUILD_ENV) \
-	  OCAMLOPT='$(FLEXLINK_OCAMLOPT) -nostdlib -I ../stdlib' flexlink.exe
+	  OCAMLOPT='$(FLEXLINK_OCAMLOPT) $(USE_STDLIB) $(SET_RELATIVE_STDLIB)' \
+	  flexlink.exe
 	cp $(FLEXDLL_SOURCE_DIR)/flexlink.exe $@
 	rm -f $(OPT_BINDIR)/flexlink$(EXE)
 	cd $(OPT_BINDIR); $(LN) $(call ROOT_FROM, $(OPT_BINDIR))/$@ flexlink$(EXE)
-	cp $(addprefix $(BYTE_BINDIR)/, $(FLEXDLL_OBJECTS)) $(OPT_BINDIR)
 
 else
 
@@ -911,8 +916,6 @@ partialclean::
 	rm -f flexlink.opt flexlink.opt.exe \
         $(OPT_BINDIR)/flexlink $(OPT_BINDIR)/flexlink.exe
 
-INSTALL_COMPLIBDIR = $(DESTDIR)$(COMPLIBDIR)
-INSTALL_FLEXDLLDIR = $(INSTALL_LIBDIR)/flexdll
 FLEXDLL_MANIFEST = default$(filter-out _i386,_$(ARCH)).manifest
 
 DOC_FILES=\
@@ -936,11 +939,14 @@ clean::
 # Build the manual latex files from the etex source files
 # (see manual/README.md)
 .PHONY: manual-pregen
-manual-pregen: opt.opt
-	cd manual; $(MAKE) clean && $(MAKE) pregen-etex
+manual-pregen: opt.opt | manual
+	$(MAKE) -C manual clean
+	$(MAKE) -C manual pregen-etex
 
+ifneq "$(wildcard manual)" ""
 clean::
 	$(MAKE) -C manual clean
+endif
 
 # The clean target
 clean:: partialclean
@@ -959,8 +965,12 @@ ocamlc_SOURCES = driver/main.mli driver/main.ml
 
 ocamlc_BYTECODE_LINKFLAGS = -compat-32 -g
 
+ifeq "$(IN_COREBOOT_CYCLE)" "true"
+ocamlc_BYTECODE_LINKFLAGS += -set-runtime-default standard_library_default=.
+endif
+
 partialclean::
-	rm -f ocamlc ocamlc.exe ocamlc.opt ocamlc.opt.exe
+	rm -f ocamlc ocamlc.exe ocamlc.opt ocamlc.opt.exe ocamlc*.stripped
 
 # The native-code compiler
 
@@ -971,7 +981,7 @@ ocamlopt_SOURCES = driver/optmain.mli driver/optmain.ml
 ocamlopt_BYTECODE_LINKFLAGS = -g
 
 partialclean::
-	rm -f ocamlopt ocamlopt.exe ocamlopt.opt ocamlopt.opt.exe
+	rm -f ocamlopt ocamlopt.exe ocamlopt.opt ocamlopt.opt.exe ocamlopt*.stripped
 
 # The toplevel
 
@@ -1095,12 +1105,12 @@ otherlibs/dynlink.depend: beforedepend
 	  otherlibs/dynlink/native/dynlink.ml \
 	  >> $@
 
-# Cleanup the lexer
+# Cleanup the lexers
 
 partialclean::
-	rm -f parsing/lexer.ml
+	rm -f tools/byterntm.ml parsing/lexer.ml
 
-beforedepend:: parsing/lexer.ml
+beforedepend:: tools/byterntm.ml parsing/lexer.ml
 
 # The predefined exceptions and primitives
 
@@ -1259,7 +1269,7 @@ runtime_NATIVE_C_SOURCES = \
 
 ## Header files generated by configure
 runtime_CONFIGURED_HEADERS = \
-  $(addprefix runtime/caml/, exec.h m.h s.h version.h)
+  runtime/sys_int.h $(addprefix runtime/caml/, exec.h m.h s.h version.h)
 
 ## Header files generated by make
 runtime_BUILT_HEADERS = $(addprefix runtime/, \
@@ -1267,22 +1277,21 @@ runtime_BUILT_HEADERS = $(addprefix runtime/, \
 
 ## Targets to build and install
 
-runtime_PROGRAMS = runtime/ocamlrun$(EXE)
-runtime_BYTECODE_STATIC_LIBRARIES = $(addprefix runtime/, \
-  ld.conf libcamlrun.$(A))
+runtime_PROGRAMS = ocamlrun
+runtime_BYTECODE_STATIC_LIBRARIES = runtime/libcamlrun.$(A)
 runtime_BYTECODE_SHARED_LIBRARIES =
 runtime_NATIVE_STATIC_LIBRARIES = \
   runtime/libasmrun.$(A) runtime/libcomprmarsh.$(A)
 runtime_NATIVE_SHARED_LIBRARIES =
 
 ifeq "$(RUNTIMED)" "true"
-runtime_PROGRAMS += runtime/ocamlrund$(EXE)
+runtime_PROGRAMS += ocamlrund
 runtime_BYTECODE_STATIC_LIBRARIES += runtime/libcamlrund.$(A)
 runtime_NATIVE_STATIC_LIBRARIES += runtime/libasmrund.$(A)
 endif
 
 ifeq "$(INSTRUMENTED_RUNTIME)" "true"
-runtime_PROGRAMS += runtime/ocamlruni$(EXE)
+runtime_PROGRAMS += ocamlruni
 runtime_BYTECODE_STATIC_LIBRARIES += runtime/libcamlruni.$(A)
 runtime_NATIVE_STATIC_LIBRARIES += runtime/libasmruni.$(A)
 endif
@@ -1290,9 +1299,9 @@ endif
 ifeq "$(UNIX_OR_WIN32)" "unix"
 ifeq "$(SUPPORTS_SHARED_LIBRARIES)" "true"
 runtime_BYTECODE_STATIC_LIBRARIES += runtime/libcamlrun_pic.$(A)
-runtime_BYTECODE_SHARED_LIBRARIES += runtime/libcamlrun_shared.$(SO)
+runtime_BYTECODE_SHARED_LIBRARIES += camlrun
 runtime_NATIVE_STATIC_LIBRARIES += runtime/libasmrun_pic.$(A)
-runtime_NATIVE_SHARED_LIBRARIES += runtime/libasmrun_shared.$(SO)
+runtime_NATIVE_SHARED_LIBRARIES += asmrun
 endif
 endif
 
@@ -1343,13 +1352,15 @@ ocamlruni_CPPFLAGS = $(runtime_CPPFLAGS) -DCAML_INSTR
 
 .PHONY: runtime-all
 runtime-all: \
-  $(runtime_BYTECODE_STATIC_LIBRARIES) $(runtime_BYTECODE_SHARED_LIBRARIES) \
-  $(runtime_PROGRAMS) $(SAK)
+  $(runtime_BYTECODE_STATIC_LIBRARIES) \
+  $(runtime_BYTECODE_SHARED_LIBRARIES:%=runtime/lib%_shared$(EXT_DLL)) \
+  $(runtime_PROGRAMS:%=runtime/%$(EXE)) $(SAK)
 
 .PHONY: runtime-allopt
 ifeq "$(NATIVE_COMPILER)" "true"
 runtime-allopt: \
-  $(runtime_NATIVE_STATIC_LIBRARIES) $(runtime_NATIVE_SHARED_LIBRARIES)
+  $(runtime_NATIVE_STATIC_LIBRARIES) \
+  $(runtime_NATIVE_SHARED_LIBRARIES:%=runtime/lib%_shared$(EXT_DLL))
 else
 runtime-allopt:
 	$(error The build has been configured with --disable-native-compiler)
@@ -1357,10 +1368,6 @@ endif
 
 ## Generated non-object files
 
-runtime/ld.conf: $(ROOTDIR)/Makefile.config
-	$(V_GEN)echo "$(STUBLIBDIR)" > $@ && \
-	echo "$(LIBDIR)" >> $@
-
 runtime/primitives: runtime/gen_primitives.sh $(runtime_BYTECODE_C_SOURCES)
 	$(V_GEN)runtime/gen_primitives.sh $@ $(runtime_BYTECODE_C_SOURCES)
 
@@ -1396,12 +1403,19 @@ $(SAK): runtime/sak.$(O)
 runtime/sak.$(O): runtime/sak.c runtime/caml/misc.h runtime/caml/config.h
 	$(V_CC)$(SAK_CC) $(SAK_CFLAGS) $(OUTPUTOBJ)$@ -c $<
 
-C_LITERAL = $(shell $(SAK) encode-C-literal '$(1)')
+C_LITERAL = $(shell $(SAK) encode-C-literal $(call QUOTE_SINGLE,$(1)))
+
+runtime/build_config.h: $(ROOTDIR)/Makefile.config \
+                        $(ROOTDIR)/Makefile.build_config $(SAK)
+	$(V_GEN){ \
+	  echo '/* This file is generated from $(ROOTDIR)/Makefile.config */'; \
+	  printf '#define OCAML_STDLIB_DIR %s\n' \
+	         $(call QUOTE_SINGLE,$(call C_LITERAL,$(TARGET_LIBDIR))); \
+	  echo '#define HOST "$(HOST)"'; \
+	  echo '#define BYTECODE_RUNTIME_ID "$(BYTECODE_RUNTIME_ID)"'; \
+	} > $@
 
-runtime/build_config.h: $(ROOTDIR)/Makefile.config $(SAK)
-	$(V_GEN)echo '/* This file is generated from $(ROOTDIR)/Makefile.config */' > $@ && \
-	echo '#define OCAML_STDLIB_DIR $(call C_LITERAL,$(LIBDIR))' >> $@ && \
-	echo '#define HOST "$(HOST)"' >> $@
+runtime/prims.$(O): runtime/build_config.h
 
 ## Runtime libraries and programs
 
@@ -1612,7 +1626,7 @@ makeruntime: runtime-all
 stdlib/libcamlrun.$(A): runtime-all
 	cd stdlib; $(LN) ../runtime/libcamlrun.$(A) .
 clean::
-	rm -f $(addprefix runtime/, *.o *.obj *.a *.lib *.so *.dll ld.conf)
+	rm -f $(addprefix runtime/, *.o *.obj *.a *.lib *.so *.dll)
 	rm -f $(addprefix runtime/, ocamlrun ocamlrund ocamlruni ocamlruns sak)
 	rm -f $(addprefix runtime/, \
 	  ocamlrun.exe ocamlrund.exe ocamlruni.exe ocamlruns.exe sak.exe)
@@ -1702,6 +1716,10 @@ ocamllex.opt: ocamlopt
 
 ocamllex_BYTECODE_LINKFLAGS = -compat-32
 
+ifeq "$(IN_COREBOOT_CYCLE)" "true"
+ocamllex_BYTECODE_LINKFLAGS += -set-runtime-default standard_library_default=.
+endif
+
 partialclean::
 	rm -f lex/*.cm* lex/*.o lex/*.obj \
         $(ocamllex_PROGRAMS) $(ocamllex_PROGRAMS:=.exe) \
@@ -1861,6 +1879,13 @@ OCAMLDOC_LIBCMTS=$(OCAMLDOC_LIBMLIS:.mli=.cmt) $(OCAMLDOC_LIBMLIS:.mli=.cmti)
 ocamldoc/%: CAMLC = $(BEST_OCAMLC) $(STDLIBFLAGS)
 ocamldoc/%: CAMLOPT = $(BEST_OCAMLOPT) $(STDLIBFLAGS)
 
+ifeq "$(SUPPORTS_SHARED_LIBRARIES)" "false"
+# ocamldoc needs a custom runtime when building statically owing to the C stubs
+# in unix.cma and str.cma. This is specified explicitly to suppress the default
+# linking flags (see $(MAYBE_ADD_BYTECODE_LAUNCHER_FLAGS) in Makefile.common)
+ocamldoc/ocamldoc$(EXE): ocamldoc_BYTECODE_LINKFLAGS += -custom
+endif
+
 .PHONY: ocamldoc
 ocamldoc: ocamldoc/ocamldoc$(EXE) ocamldoc/odoc_test.cmo
 
@@ -1989,7 +2014,7 @@ $(asmgen_OBJECT): $(asmgen_SOURCE)
 	$(V_ASM)$(ASPP) $(OC_ASPPFLAGS) -o $@ $< || $(ASPP_ERROR)
 endif
 
-test_in_prefix_SOURCES = $(addprefix testsuite/tools/,\
+test_in_prefix_SOURCES = tools/byterntm.mll $(addprefix testsuite/tools/,\
   stubs.c \
   harness.mli harness.ml \
   toolchain.mli toolchain.ml \
@@ -2014,12 +2039,24 @@ testsuite/tools/test_in_prefi%: CAMLC = $(BEST_OCAMLC) $(STDLIBFLAGS)
 
 test_in_prefix_BYTECODE_LINKFLAGS += -custom
 
+ifeq "$(TARGET_LIBDIR_IS_RELATIVE)" "true"
+# testsuite/tools/test_in_prefix cannot use a relative stdlib because it is run
+# from testsuite/tools, not from the installation tree (the alternative would be
+# to compile it directly with the installed compiler)
+test_in_prefix_NATIVE_LINKFLAGS =
+test_in_prefix_COMMON_LINKFLAGS = \
+  -set-runtime-default 'standard_library_default=$(LIBDIR)'
+endif
+
 testsuite/tools/test_in_prefi%: CAMLOPT = $(BEST_OCAMLOPT) $(STDLIBFLAGS)
 
 testsuite/tools/dump_load_path$(EXE): \
   testsuite/tools/dump_load_path.$(O) runtime/prims.$(O) runtime/libcamlrun.$(A)
 	$(V_MKEXE)$(MKEXE) -o $@ $^ $(BYTECCLIBS)
 
+testsuite/tools/poisonedruntime$(EXE): testsuite/tools/poisonedruntime.$(O)
+	$(V_MKEXE)$(call MKEXE_VIA_CC,$@,$^)
+
 ocamltest_BYTECODE_LINKFLAGS = -custom -g
 
 ocamltest/ocamltest$(EXE): ocamlc ocamlyacc ocamllex
@@ -2067,6 +2104,7 @@ partialclean::
 	rm -f $(addprefix testsuite/tools/*.,cm* o obj a lib)
 	rm -f testsuite/tools/codegen testsuite/tools/codegen.exe
 	rm -f testsuite/tools/dump_load_path testsuite/tools/dump_load_path.exe
+	rm -f testsuite/tools/poisonedruntime testsuite/tools/poisonedruntime.exe
 	rm -f testsuite/tools/expect testsuite/tools/expect.exe
 	rm -f testsuite/tools/test_in_prefix testsuite/tools/test_in_prefix.exe
 	rm -f testsuite/tools/test_in_prefix.opt \
@@ -2220,6 +2258,13 @@ debugger/ocamldebug.cmo: $(ocamldebug_DEBUGGER_OBJECTS)
 
 debugger/ocamldebug_entry.cmo: debugger/ocamldebug.cmo
 
+ifeq "$(SUPPORTS_SHARED_LIBRARIES)" "false"
+# ocamldebug needs a custom runtime when building statically owing to the
+# C stubs in unix.cma. This is specified explicitly to suppress the default
+# linking flags (see $(MAYBE_ADD_BYTECODE_LAUNCHER_FLAGS) in Makefile.common)
+debugger/ocamldebug$(EXE): ocamldebug_BYTECODE_LINKFLAGS += -custom
+endif
+
 clean::
 	rm -f debugger/ocamldebug debugger/ocamldebug.exe
 	rm -f debugger/debugger_lexer.ml
@@ -2451,7 +2496,7 @@ beforedepend:: $(addprefix tools/,opnames.ml make_opcodes.ml)
 
 ocamlobjinfo_LIBRARIES = \
   $(addprefix compilerlibs/,ocamlcommon ocamlbytecomp ocamlmiddleend)
-ocamlobjinfo_SOURCES = tools/objinfo.mli tools/objinfo.ml
+ocamlobjinfo_SOURCES = tools/byterntm.mll tools/objinfo.mli tools/objinfo.ml
 
 # Scan object files for required primitives
 
@@ -2488,6 +2533,13 @@ $(ocamltex): VPATH += $(addprefix otherlibs/,str unix)
 
 tools/ocamltex.cmo: OC_COMMON_COMPFLAGS += -no-alias-deps
 
+ifeq "$(SUPPORTS_SHARED_LIBRARIES)" "false"
+# ocamltex needs a custom runtime when building statically owing to the C stubs
+# in unix.cma and str.cma. This is specified explicitly to suppress the default
+# linking flags (see $(MAYBE_ADD_BYTECODE_LAUNCHER_FLAGS) in Makefile.common)
+tools/ocamltex$(EXE): ocamltex_BYTECODE_LINKFLAGS += -custom
+endif
+
 # we need str and unix which depend on the bytecode version of other tools
 # thus we use the othertools target
 ## Test compilation of backend-specific parts
@@ -2664,7 +2716,9 @@ distclean: clean
 ifneq "$(FLEXDLL_SUBMODULE_PRESENT)" ""
 	$(MAKE) -C flexdll distclean MSVC_DETECT=0
 endif
+ifneq "$(wildcard manual)" ""
 	$(MAKE) -C manual distclean
+endif
 	rm -f ocamldoc/META
 	rm -f $(addprefix ocamltest/,ocamltest_config.ml ocamltest_unix.ml)
 	rm -f testsuite/tools/toolchain.ml
@@ -2673,7 +2727,7 @@ endif
 	  otherlibs/dynlink/dynlink_cmxs_format.mli \
 	  otherlibs/dynlink/dynlink_platform_intf.mli
 	$(MAKE) -C otherlibs distclean
-	rm -f $(runtime_CONFIGURED_HEADERS)
+	rm -f $(runtime_CONFIGURED_HEADERS) runtime/ld.conf
 	$(MAKE) -C stdlib distclean
 	$(MAKE) -C testsuite distclean
 	rm -f tools/eventlog_metadata tools/*.bak
@@ -2687,320 +2741,337 @@ endif
          $(BYTE_BUILD_TREE) $(OPT_BUILD_TREE)
 	rm -f config.log config.status libtool
 
-INSTALL_LIBDIR_DYNLINK = $(INSTALL_LIBDIR)/dynlink
+# COMPILER_ARTEFACT_DIRS adds the common compiler-libs directories as prefixes
+# to a sequence of patterns in the first argument, e.g.
+# $(call COMPILER_ARTEFACT_DIRS, *.cmi) expands to utils/*.cmi, parsing/*.cmi,
+# and so forth. Multiple wildcard patterns may be supplied. An optional second
+# argument includes additional directories beyond the common ones (e.g. asmcomp,
+# etc.)
+COMPILER_ARTEFACT_DIRS = \
+  $(foreach dir, \
+      utils parsing typing bytecomp file_formats lambda driver toplevel \
+      $(if $(filter-out undefined, $(origin 2)), $(2)), \
+    $(addprefix $(dir)/, $(1)))
+NATIVE_ARTEFACT_DIRS = \
+  asmcomp toplevel/native \
+  middle_end middle_end/closure middle_end/flambda middle_end/flambda/base_types
 
 # Installation
-.PHONY: install
-install:
-	$(MKDIR) "$(INSTALL_BINDIR)"
-	$(MKDIR) "$(INSTALL_LIBDIR)"
-	$(MKDIR) "$(INSTALL_STUBLIBDIR)"
-	$(MKDIR) "$(INSTALL_COMPLIBDIR)"
-	$(MKDIR) "$(INSTALL_DOCDIR)"
-	$(MKDIR) "$(INSTALL_INCDIR)"
-	$(MKDIR) "$(INSTALL_LIBDIR_PROFILING)"
-	$(INSTALL_PROG) $(runtime_PROGRAMS) "$(INSTALL_BINDIR)"
-	$(INSTALL_DATA) $(runtime_BYTECODE_STATIC_LIBRARIES) \
-	  "$(INSTALL_LIBDIR)"
-ifneq "$(runtime_BYTECODE_SHARED_LIBRARIES)" ""
-	$(INSTALL_PROG) $(runtime_BYTECODE_SHARED_LIBRARIES) \
-	  "$(INSTALL_LIBDIR)"
-endif
-	$(INSTALL_DATA) runtime/caml/domain_state.tbl runtime/caml/*.h \
-	  "$(INSTALL_INCDIR)"
-	$(INSTALL_PROG) ocaml$(EXE) "$(INSTALL_BINDIR)"
+# Historically, the install target dynamically installed what had been built,
+# for example, if only world had been built then make install simply didn't
+# install the native tools. That infrastructure is potentially convenient when
+# working on the compiler, but potentially masks bugs. It is better to have the
+# installation targets require everything configure mandated to have built.
+# There are three entry points to installation:
+#   install - installs everything
+#   installopt - installs the native code compiler _and_ the extra .opt tools
+#   installoptopt - installs just the extra .opt tools
+# The installopt targets have been maintained for now, but may be removed in the
+# future.
+
+ifeq "$(NATIVE_COMPILER)" "true"
+install: full-installoptopt
+	$(call INSTALL_END)
+else
+install: common-install
+	$(call INSTALL_END)
+endif
+
+# These three targets are the slightly esoteric special sauce that avoid
+# recursive make invocations in the install targets.
+# There are three basic install recipes:
+# - The old install target is available to common-install, but never recurses to
+#   installopt
+# - The old installopt target is available as both full-installopt and
+#   native-install
+# - The old installoptopt target is also available as full-installoptopt and
+#   installopt
+# These sets of recipes are then welded together by these three dependency
+# specifications
+# - When configured with --disable-native-compiler, the install target simply
+#   depends on common-install (see above)
+# - Otherwise, install depends on full-installoptopt (see above)
+# - The recipe for full-installoptopt installs the .opt versions of the tools,
+#   but it _depends on_ full-installopt.
+# - full-installopt installs the native compiler, but it _depends on_
+#   common-install
+installopt: native-install
+
+full-installopt:: common-install
+
+full-installoptopt: full-installopt
+
+.PHONY: common-install
+common-install::
+	$(call INSTALL_BEGIN)
+
+ifeq "$(SUFFIXING)" "true"
+MANGLE_RUNTIME_NAME = $(TARGET)-$(1)-$(BYTECODE_RUNTIME_ID)$(EXE)
+MANGLE_RUNTIME_DLL_NAME = lib$(1)-$(TARGET)-$($(2)_RUNTIME_ID)$(EXT_DLL)
+else
+MANGLE_RUNTIME_NAME = $(1)$(EXE)
+MANGLE_RUNTIME_DLL_NAME = lib$(1)_shared$(EXT_DLL)
+endif
+
+define INSTALL_RUNTIME
+common-install::
+	$$(call INSTALL_ITEM, runtime/$(1)$(EXE), bin, , \
+	  $(call MANGLE_RUNTIME_NAME,$(1)), $(if $(filter true, $(SUFFIXING)), \
+	    $(1)$(EXE) $(1)-$(ZINC_RUNTIME_ID)$(EXE)))
+endef
+define INSTALL_RUNTIME_LIB
+ifeq "$(2)" "BYTECODE"
+common-install::
+else
+full-installopt native-install::
+endif
+	$$(call INSTALL_ITEM, runtime/lib$(1)_shared$(EXT_DLL), libexec, , \
+	  $(call MANGLE_RUNTIME_DLL_NAME,$(1),$(2)), \
+	    $(if $(filter true, $(SUFFIXING)), lib$(1)_shared$(EXT_DLL)))
+endef
+
+$(foreach runtime, $(runtime_PROGRAMS), \
+  $(eval $(call INSTALL_RUNTIME,$(runtime))))
+
+common-install::
+	$(call INSTALL_ITEMS, runtime/ld.conf $(runtime_BYTECODE_STATIC_LIBRARIES), \
+	  lib)
+
+$(foreach shared_runtime, $(runtime_BYTECODE_SHARED_LIBRARIES), \
+  $(eval $(call INSTALL_RUNTIME_LIB,$(shared_runtime),BYTECODE)))
+
+common-install::
+	$(call INSTALL_ITEMS, \
+	    runtime/caml/domain_state.tbl runtime/caml/*.h, \
+	  lib, $(INSTALL_LIBDIR_CAML))
+	$(call INSTALL_ITEMS, ocaml$(EXE), bin)
 ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
-	$(call INSTALL_STRIPPED_BYTE_PROG,\
-               ocamlc$(EXE),"$(INSTALL_BINDIR)/ocamlc.byte$(EXE)")
+	$(call STRIP_BYTE_PROG, ocamlc$(EXE))
+ifeq "$(NATIVE_COMPILER)" "true"
+	$(call INSTALL_ITEM, \
+	  ocamlc$(EXE).stripped, bin, , ocamlc.byte$(EXE))
+else
+	$(call INSTALL_ITEM, \
+	  ocamlc$(EXE).stripped, bin, , ocamlc.byte$(EXE), ocamlc$(EXE))
+endif
 endif
 	$(MAKE) -C stdlib install
+
+define INSTALL_ONE_NAT_TOOL
+common-install::
+ifeq "$(NATIVE_COMPILER)" "true"
 ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
-	$(INSTALL_PROG) lex/ocamllex$(EXE) \
-	  "$(INSTALL_BINDIR)/ocamllex.byte$(EXE)"
-	for i in $(TOOLS_TO_INSTALL_NAT); \
-	do \
-	  $(INSTALL_PROG) "tools/$$i$(EXE)" "$(INSTALL_BINDIR)/$$i.byte$(EXE)";\
-	  if test -f "tools/$$i".opt$(EXE); then \
-	    $(INSTALL_PROG) "tools/$$i.opt$(EXE)" "$(INSTALL_BINDIR)" && \
-	    (cd "$(INSTALL_BINDIR)" && $(LN) "$$i.opt$(EXE)" "$$i$(EXE)"); \
-	  else \
-	    (cd "$(INSTALL_BINDIR)" && $(LN) "$$i.byte$(EXE)" "$$i$(EXE)"); \
-	  fi; \
-	done
+	$$(call INSTALL_ITEM, tools/$(1)$(EXE), bin, , $(1).byte$(EXE))
+endif
+	$$(call INSTALL_ITEM, tools/$(1).opt$(EXE), bin, , , $(1)$(EXE))
 else
-	for i in $(TOOLS_TO_INSTALL_NAT); \
-	do \
-	  if test -f "tools/$$i".opt$(EXE); then \
-	    $(INSTALL_PROG) "tools/$$i.opt$(EXE)" "$(INSTALL_BINDIR)"; \
-	    (cd "$(INSTALL_BINDIR)" && $(LN) "$$i.opt$(EXE)" "$$i$(EXE)"); \
-	  fi; \
-	done
+	$$(call INSTALL_ITEM, tools/$(1)$(EXE), bin, , $(1).byte$(EXE), $(1)$(EXE))
 endif
-	for i in $(TOOLS_TO_INSTALL_BYT); \
-	do \
-	  $(INSTALL_PROG) "tools/$$i$(EXE)" "$(INSTALL_BINDIR)";\
-	done
-	$(INSTALL_PROG) $(ocamlyacc_PROGRAM)$(EXE) "$(INSTALL_BINDIR)"
-	$(INSTALL_DATA) \
-	   utils/*.cmi \
-	   parsing/*.cmi \
-	   typing/*.cmi \
-	   bytecomp/*.cmi \
-	   file_formats/*.cmi \
-	   lambda/*.cmi \
-	   driver/*.cmi \
-	   toplevel/*.cmi \
-	   "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	   toplevel/byte/*.cmi \
-	   "$(INSTALL_COMPLIBDIR)"
+endef
+
+ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
+common-install::
+ifeq "$(NATIVE_COMPILER)" "true"
+	$(call INSTALL_ITEM, \
+	  lex/ocamllex$(EXE), bin, , ocamllex.byte$(EXE))
+else
+	$(call INSTALL_ITEM, \
+	  lex/ocamllex$(EXE), bin, , ocamllex.byte$(EXE), ocamllex$(EXE))
+endif
+endif
+
+$(foreach tool, $(TOOLS_TO_INSTALL_NAT), \
+  $(eval $(call INSTALL_ONE_NAT_TOOL,$(tool))))
+
+define INSTALL_ONE_BYT_TOOL
+common-install::
+	$$(call INSTALL_ITEMS, tools/$(1)$(EXE), bin)
+endef
+
+$(foreach tool, $(TOOLS_TO_INSTALL_BYT), \
+  $(eval $(call INSTALL_ONE_BYT_TOOL,$(tool))))
+
+common-install::
+	$(call INSTALL_ITEMS, $(ocamlyacc_PROGRAM)$(EXE), bin)
+	$(call INSTALL_ITEMS, \
+	    $(call COMPILER_ARTEFACT_DIRS, *.cmi), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	   utils/*.cmt utils/*.cmti utils/*.mli \
-	   parsing/*.cmt parsing/*.cmti parsing/*.mli \
-	   typing/*.cmt typing/*.cmti typing/*.mli \
-	   file_formats/*.cmt file_formats/*.cmti file_formats/*.mli \
-	   lambda/*.cmt lambda/*.cmti lambda/*.mli \
-	   bytecomp/*.cmt bytecomp/*.cmti bytecomp/*.mli \
-	   driver/*.cmt driver/*.cmti driver/*.mli \
-	   toplevel/*.cmt toplevel/*.cmti toplevel/*.mli \
-	   "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	   toplevel/byte/*.cmt \
-	   "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	  tools/profiling.cmt tools/profiling.cmti \
-	  "$(INSTALL_LIBDIR_PROFILING)"
-endif
-	$(INSTALL_DATA) \
-	  compilerlibs/*.cma compilerlibs/META \
-	  "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	   $(ocamlc_CMO_FILES) $(ocaml_CMO_FILES) \
-	   "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_PROG) $(expunge) "$(INSTALL_LIBDIR)"
+	$(call INSTALL_ITEMS, \
+	    $(call COMPILER_ARTEFACT_DIRS, *.cmt *.cmti *.mli), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, toplevel/byte/*.cmt, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, tools/profiling.cmt tools/profiling.cmti, \
+	  lib, $(INSTALL_LIBDIR_PROFILING))
+endif
+	$(call INSTALL_ITEMS, compilerlibs/*.cma compilerlibs/META, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, $(ocamlc_CMO_FILES) $(ocaml_CMO_FILES), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, $(expunge), libexec)
 # If installing over a previous OCaml version, ensure some modules are removed
 # from the previous installation.
-	rm -f "$(INSTALL_LIBDIR)"/topdirs.cm* "$(INSTALL_LIBDIR)/topdirs.mli"
-	rm -f "$(INSTALL_LIBDIR)"/profiling.cm* "$(INSTALL_LIBDIR)/profiling.$(O)"
-	$(INSTALL_DATA) \
-	  tools/profiling.cmi tools/profiling.cmo \
-	  "$(INSTALL_LIBDIR_PROFILING)"
+	$(call INSTALL_RM, \
+	  "$(INSTALL_LIBDIR)"/topdirs.cm* "$(INSTALL_LIBDIR)/topdirs.mli")
+	$(call INSTALL_RM, \
+	  "$(INSTALL_LIBDIR)"/profiling.cm* "$(INSTALL_LIBDIR)/profiling.$(O)")
+	$(call INSTALL_ITEMS, tools/profiling.cmi tools/profiling.cmo, \
+	  lib, $(INSTALL_LIBDIR_PROFILING))
 ifeq "$(UNIX_OR_WIN32)" "unix" # Install manual pages only on Unix
 	$(MAKE) -C man install
 endif
 # For dynlink, if installing over a previous OCaml version, ensure
 # dynlink is removed from the previous installation.
-	rm -f "$(INSTALL_LIBDIR)"/dynlink.cm* "$(INSTALL_LIBDIR)/dynlink.mli" \
-        "$(INSTALL_LIBDIR)/dynlink.$(A)" \
-        $(addprefix "$(INSTALL_LIBDIR)/", $(notdir $(dynlink_CMX_FILES)))
-	$(MKDIR) "$(INSTALL_LIBDIR_DYNLINK)"
-	$(INSTALL_DATA) \
-	  otherlibs/dynlink/dynlink.cmi otherlibs/dynlink/dynlink.cma \
-	  otherlibs/dynlink/META \
-	  "$(INSTALL_LIBDIR_DYNLINK)"
+	$(call INSTALL_RM, \
+	  "$(INSTALL_LIBDIR)"/dynlink.cm* \
+	  "$(INSTALL_LIBDIR)/dynlink.mli" \
+	  "$(INSTALL_LIBDIR)/dynlink.$(A)" \
+	  $(addprefix "$(INSTALL_LIBDIR)/", $(notdir $(dynlink_CMX_FILES))))
+	$(call INSTALL_ITEMS, \
+	    otherlibs/dynlink/dynlink.cmi otherlibs/dynlink/dynlink.cma \
+	    otherlibs/dynlink/META, \
+	  lib, $(INSTALL_LIBDIR_DYNLINK))
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	  otherlibs/dynlink/dynlink.cmti otherlibs/dynlink/dynlink.mli \
-	  "$(INSTALL_LIBDIR_DYNLINK)"
+	$(call INSTALL_ITEMS, \
+	    otherlibs/dynlink/dynlink.cmti otherlibs/dynlink/dynlink.mli, \
+	  lib, $(INSTALL_LIBDIR_DYNLINK))
 endif
 	for i in $(OTHERLIBS); do \
 	  $(MAKE) -C otherlibs/$$i install || exit $$?; \
 	done
 ifeq "$(build_ocamldoc)" "true"
-	$(MKDIR) "$(INSTALL_LIBDIR)/ocamldoc"
-	$(INSTALL_PROG) $(OCAMLDOC) "$(INSTALL_BINDIR)"
-	$(INSTALL_DATA) \
-	  ocamldoc/ocamldoc.hva ocamldoc/*.cmi ocamldoc/odoc_info.cma \
-	  ocamldoc/META \
-	  "$(INSTALL_LIBDIR)/ocamldoc"
-	$(INSTALL_DATA) \
-	  $(OCAMLDOC_LIBCMIS) \
-	  "$(INSTALL_LIBDIR)/ocamldoc"
+	$(call INSTALL_ITEMS, ocamldoc/ocamldoc$(EXE), bin)
+	$(call INSTALL_ITEMS, \
+	    ocamldoc/ocamldoc.hva ocamldoc/*.cmi ocamldoc/odoc_info.cma \
+	    ocamldoc/META, \
+	  lib, $(INSTALL_LIBDIR_OCAMLDOC))
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	  $(OCAMLDOC_LIBMLIS) $(OCAMLDOC_LIBCMTS) \
-	  "$(INSTALL_LIBDIR)/ocamldoc"
+	$(call INSTALL_ITEMS, $(OCAMLDOC_LIBMLIS) $(OCAMLDOC_LIBCMTS), \
+	  lib, $(INSTALL_LIBDIR_OCAMLDOC))
 endif
 endif
 ifeq "$(build_libraries_manpages)" "true"
 	$(MAKE) -C api_docgen install
 endif
-	if test -n "$(WITH_DEBUGGER)"; then \
-	  $(INSTALL_PROG) debugger/ocamldebug$(EXE) "$(INSTALL_BINDIR)"; \
-	fi
+ifneq "$(WITH_DEBUGGER)" ""
+	$(call INSTALL_ITEMS, debugger/ocamldebug$(EXE), bin)
+endif
 ifeq "$(BOOTSTRAPPING_FLEXDLL)" "true"
 ifeq "$(TOOLCHAIN)" "msvc"
-	$(INSTALL_DATA) $(FLEXDLL_SOURCE_DIR)/$(FLEXDLL_MANIFEST) \
-    "$(INSTALL_BINDIR)/"
+	# Technically this should not be installed with "executable"
+	# permissions, but in practice that request will be ignored.
+	$(call INSTALL_ITEMS, $(FLEXDLL_SOURCE_DIR)/$(FLEXDLL_MANIFEST), bin)
 endif
 ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
-	$(INSTALL_PROG) \
-	  flexlink.byte$(EXE) "$(INSTALL_BINDIR)"
-endif # ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
-	$(MKDIR) "$(INSTALL_FLEXDLLDIR)"
-	$(INSTALL_DATA) $(addprefix $(BYTE_BINDIR)/, $(FLEXDLL_OBJECTS)) \
-    "$(INSTALL_FLEXDLLDIR)"
-endif # ifeq "$(BOOTSTRAPPING_FLEXDLL)" "true"
-	$(INSTALL_DATA) Makefile.config "$(INSTALL_LIBDIR)"
-	$(INSTALL_DATA) $(DOC_FILES) "$(INSTALL_DOCDIR)"
-ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
-	if test -f ocamlopt$(EXE); then $(MAKE) installopt; else \
-	   cd "$(INSTALL_BINDIR)"; \
-	   $(LN) ocamlc.byte$(EXE) ocamlc$(EXE); \
-	   $(LN) ocamllex.byte$(EXE) ocamllex$(EXE); \
-	   (test -f flexlink.byte$(EXE) && \
-	      $(LN) flexlink.byte$(EXE) flexlink$(EXE)) || true; \
-	fi
+ifeq "$(NATIVE_COMPILER)" "true"
+	$(call INSTALL_ITEMS, flexlink.byte$(EXE), bin)
 else
-	if test -f ocamlopt$(EXE); then $(MAKE) installopt; fi
+	$(call INSTALL_ITEM, flexlink.byte$(EXE), bin, , , flexlink$(EXE))
 endif
+endif # ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
+	$(call INSTALL_ITEMS, $(FLEXDLL_OBJECTS), lib, $(INSTALL_LIBDIR_FLEXDLL))
+endif # ifeq "$(BOOTSTRAPPING_FLEXDLL)" "true"
+	$(call INSTALL_ITEMS, Makefile.config, lib)
+	$(call INSTALL_ITEMS, $(DOC_FILES), doc)
 
 # Installation of the native-code compiler
-.PHONY: installopt
-installopt:
-	$(INSTALL_DATA) $(runtime_NATIVE_STATIC_LIBRARIES) "$(INSTALL_LIBDIR)"
-ifneq "$(runtime_NATIVE_SHARED_LIBRARIES)" ""
-	$(INSTALL_PROG) $(runtime_NATIVE_SHARED_LIBRARIES) "$(INSTALL_LIBDIR)"
-endif
+.PHONY: full-installopt native-install
+full-installopt native-install::
+	$(call INSTALL_ITEMS, $(runtime_NATIVE_STATIC_LIBRARIES), lib)
+
+$(foreach shared_runtime, $(runtime_NATIVE_SHARED_LIBRARIES), \
+  $(eval $(call INSTALL_RUNTIME_LIB,$(shared_runtime),NATIVE)))
+
+full-installopt native-install::
 ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
-	$(call INSTALL_STRIPPED_BYTE_PROG,\
-               ocamlopt$(EXE),"$(INSTALL_BINDIR)/ocamlopt.byte$(EXE)")
+	$(call STRIP_BYTE_PROG, ocamlopt$(EXE))
+	$(call INSTALL_ITEM, ocamlopt$(EXE).stripped, bin, , ocamlopt.byte$(EXE))
 endif
 	$(MAKE) -C stdlib installopt
-	$(INSTALL_DATA) \
-	    middle_end/*.cmi \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    middle_end/closure/*.cmi \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    middle_end/flambda/*.cmi \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    middle_end/flambda/base_types/*.cmi \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    asmcomp/*.cmi \
-	    "$(INSTALL_COMPLIBDIR)"
+	$(call INSTALL_ITEMS, \
+	    middle_end/*.cmi, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    middle_end/closure/*.cmi, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    middle_end/flambda/*.cmi, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    middle_end/flambda/base_types/*.cmi, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    asmcomp/*.cmi, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	    middle_end/*.cmt middle_end/*.cmti \
-	    middle_end/*.mli \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    middle_end/closure/*.cmt middle_end/closure/*.cmti \
-	    middle_end/closure/*.mli \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    middle_end/flambda/*.cmt middle_end/flambda/*.cmti \
-	    middle_end/flambda/*.mli \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    middle_end/flambda/base_types/*.cmt \
-            middle_end/flambda/base_types/*.cmti \
-	    middle_end/flambda/base_types/*.mli \
-	    "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	    asmcomp/*.cmt asmcomp/*.cmti \
-	    asmcomp/*.mli \
-	    "$(INSTALL_COMPLIBDIR)"
-endif
-	$(INSTALL_DATA) \
-	    $(ocamlopt_CMO_FILES) \
-	    "$(INSTALL_COMPLIBDIR)"
-ifeq "$(build_ocamldoc)" "true"
-	$(MKDIR) "$(INSTALL_LIBDIR)/ocamldoc"
-	$(INSTALL_PROG) $(OCAMLDOC_OPT) "$(INSTALL_BINDIR)"
-	$(INSTALL_DATA) \
-	  $(OCAMLDOC_LIBCMIS) \
-	  "$(INSTALL_LIBDIR)/ocamldoc"
-ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	  $(OCAMLDOC_LIBMLIS) $(OCAMLDOC_LIBCMTS) \
-	  "$(INSTALL_LIBDIR)/ocamldoc"
+	$(call INSTALL_ITEMS, \
+	    $(addprefix middle_end/, *.cmt *.cmti *.mli), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    $(addprefix middle_end/closure/, *.cmt *.cmti *.mli), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    $(addprefix middle_end/flambda/, *.cmt *.cmti *.mli), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    $(addprefix middle_end/flambda/base_types/, *.cmt *.cmti *.mli), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    $(addprefix asmcomp/, *.cmt *.cmti *.mli), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
 endif
-	$(INSTALL_DATA) \
-	  ocamldoc/ocamldoc.hva ocamldoc/*.cmx ocamldoc/odoc_info.$(A) \
-	  ocamldoc/odoc_info.cmxa \
-	  "$(INSTALL_LIBDIR)/ocamldoc"
+	$(call INSTALL_ITEMS, $(ocamlopt_CMO_FILES), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+ifeq "$(build_ocamldoc)" "true"
+	$(call INSTALL_ITEMS, ocamldoc/ocamldoc.opt$(EXE), bin)
+	$(call INSTALL_ITEMS, \
+	    ocamldoc/*.cmx ocamldoc/odoc_info.$(A) ocamldoc/odoc_info.cmxa, \
+	  lib, $(INSTALL_LIBDIR_OCAMLDOC))
 endif
 ifeq "$(strip $(NATDYNLINK))" "true"
-	$(INSTALL_DATA) \
-	  $(dynlink_CMX_FILES) otherlibs/dynlink/dynlink.cmxa \
-	  otherlibs/dynlink/dynlink.$(A) \
-	  "$(INSTALL_LIBDIR_DYNLINK)"
+	$(call INSTALL_ITEMS, \
+	    $(dynlink_CMX_FILES) otherlibs/dynlink/dynlink.cmxa \
+	    otherlibs/dynlink/dynlink.$(A), \
+	  lib, $(INSTALL_LIBDIR_DYNLINK))
 endif
 	for i in $(OTHERLIBS); do \
 	  $(MAKE) -C otherlibs/$$i installopt || exit $$?; \
 	done
-ifeq "$(INSTALL_BYTECODE_PROGRAMS)" "true"
-	if test -f ocamlopt.opt$(EXE); then $(MAKE) installoptopt; else \
-	   cd "$(INSTALL_BINDIR)"; \
-	   $(LN) ocamlc.byte$(EXE) ocamlc$(EXE); \
-	   $(LN) ocamlopt.byte$(EXE) ocamlopt$(EXE); \
-	   $(LN) ocamllex.byte$(EXE) ocamllex$(EXE); \
-	   (test -f flexlink.byte$(EXE) && \
-	     $(LN) flexlink.byte$(EXE) flexlink$(EXE)) || true; \
-	fi
-else
-	if test -f ocamlopt.opt$(EXE); then $(MAKE) installoptopt; fi
-endif
-	$(INSTALL_DATA) \
-          tools/profiling.cmx tools/profiling.$(O) \
-	  "$(INSTALL_LIBDIR_PROFILING)"
-
-.PHONY: installoptopt
-installoptopt:
-	$(INSTALL_PROG) ocamlc.opt$(EXE) "$(INSTALL_BINDIR)"
-	$(INSTALL_PROG) ocamlopt.opt$(EXE) "$(INSTALL_BINDIR)"
-	$(INSTALL_PROG) lex/ocamllex.opt$(EXE) "$(INSTALL_BINDIR)"
-	cd "$(INSTALL_BINDIR)"; \
-	   $(LN) ocamlc.opt$(EXE) ocamlc$(EXE); \
-	   $(LN) ocamlopt.opt$(EXE) ocamlopt$(EXE); \
-	   $(LN) ocamllex.opt$(EXE) ocamllex$(EXE)
+	$(call INSTALL_ITEMS, tools/profiling.cmx tools/profiling.$(O), \
+	  lib, $(INSTALL_LIBDIR_PROFILING))
+
+.PHONY: full-installoptopt installopt installoptopt
+full-installoptopt installopt installoptopt:
+	$(call INSTALL_ITEM, ocamlc.opt$(EXE), bin, , , ocamlc$(EXE))
+	$(call INSTALL_ITEM, ocamlopt.opt$(EXE), bin, , , ocamlopt$(EXE))
+	$(call INSTALL_ITEM, lex/ocamllex.opt$(EXE), bin, , , ocamllex$(EXE))
 ifeq "$(BOOTSTRAPPING_FLEXDLL)" "true"
-	$(INSTALL_PROG) flexlink.opt$(EXE) "$(INSTALL_BINDIR)"
-	cd "$(INSTALL_BINDIR)"; \
-	  $(LN) flexlink.opt$(EXE) flexlink$(EXE)
-endif
-	$(INSTALL_DATA) \
-	   utils/*.cmx parsing/*.cmx typing/*.cmx bytecomp/*.cmx \
-	   toplevel/*.cmx toplevel/native/*.cmx \
-	   toplevel/native/tophooks.cmi \
-	   file_formats/*.cmx \
-	   lambda/*.cmx \
-	   driver/*.cmx asmcomp/*.cmx middle_end/*.cmx \
-           middle_end/closure/*.cmx \
-           middle_end/flambda/*.cmx \
-           middle_end/flambda/base_types/*.cmx \
-          "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	   compilerlibs/*.cmxa compilerlibs/*.$(A) \
-	   "$(INSTALL_COMPLIBDIR)"
-	$(INSTALL_DATA) \
-	   $(ocamlc_CMX_FILES) $(ocamlc_CMX_FILES:.cmx=.$(O)) \
-	   $(ocamlopt_CMX_FILES) $(ocamlopt_CMX_FILES:.cmx=.$(O)) \
-	   $(ocamlnat_CMX_FILES:.cmx=.$(O)) \
-	   "$(INSTALL_COMPLIBDIR)"
+	$(call INSTALL_ITEM, flexlink.opt$(EXE), bin, , , flexlink$(EXE))
+endif
+	$(call INSTALL_ITEMS, \
+	    $(call COMPILER_ARTEFACT_DIRS, *.cmx, $(NATIVE_ARTEFACT_DIRS)) \
+	    toplevel/native/tophooks.cmi, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, compilerlibs/*.cmxa compilerlibs/*.$(A), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
+	$(call INSTALL_ITEMS, \
+	    $(ocamlc_CMX_FILES:.cmx=.$(O)) \
+	    $(ocamlopt_CMX_FILES:.cmx=.$(O)) \
+	    $(ocamlnat_CMX_FILES:.cmx=.$(O)), \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
 ifeq "$(INSTALL_OCAMLNAT)" "true"
-	  $(INSTALL_PROG) ocamlnat$(EXE) "$(INSTALL_BINDIR)"
+	  $(call INSTALL_ITEMS, ocamlnat$(EXE), bin)
 endif
 
 # Installation of the *.ml sources of compiler-libs
 .PHONY: install-compiler-sources
 install-compiler-sources:
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	   utils/*.ml parsing/*.ml typing/*.ml bytecomp/*.ml driver/*.ml \
-           file_formats/*.ml \
-           lambda/*.ml \
-	   toplevel/*.ml toplevel/byte/*.ml \
-	   middle_end/*.ml middle_end/closure/*.ml \
-     middle_end/flambda/*.ml middle_end/flambda/base_types/*.ml \
-	   asmcomp/*.ml \
-	   asmcmp/debug/*.ml \
-	   "$(INSTALL_COMPLIBDIR)"
+	$(call INSTALL_ITEMS, \
+	    $(call COMPILER_ARTEFACT_DIRS, *.ml, $(NATIVE_ARTEFACT_DIRS)) \
+	    toplevel/byte/*.ml, \
+	  lib, $(INSTALL_LIBDIR_COMPILERLIBS))
 endif
 
 include .depend
diff --git a/Makefile.build_config.in b/Makefile.build_config.in
index 006eb2fc59a2..c6ed402699ad 100644
--- a/Makefile.build_config.in
+++ b/Makefile.build_config.in
@@ -78,14 +78,22 @@ COMPUTE_DEPS=@compute_deps@
 # The C compiler vendor
 OCAML_CC_VENDOR = @ocaml_cc_vendor@
 
+BUILD_PATH_LOGICAL = @srcdir_abs@
+BUILD_PATH_PHYSICAL = @srcdir_abs_real@
+BUILD_MAP_FLAGS = @build_map_flags@
+BUILD_MAP_CFLAGS = $(foreach flag, $(BUILD_MAP_FLAGS), \
+  $(call QUOTE_SINGLE,$(flag)$(BUILD_PATH_LOGICAL)=+build) \
+  $(if $(BUILD_PATH_PHYSICAL), \
+    $(call $(QUOTE_SINGLE),$(flag)$(BUILD_PATH_PHYSICAL)=+build)))
+
 # Default flags to use to compile C files
-OC_CFLAGS = @oc_cflags@
+OC_CFLAGS = @oc_cflags@ $(BUILD_MAP_CFLAGS)
 
 # Flags to use when compiling C files to be linked with bytecode
-OC_BYTECODE_CFLAGS = @oc_bytecode_cflags@
+OC_BYTECODE_CFLAGS = @oc_bytecode_cflags@ $(BUILD_MAP_CFLAGS)
 
 # Flags to use when compiling C files to be linked with native code
-OC_NATIVE_CFLAGS = @oc_native_cflags@
+OC_NATIVE_CFLAGS = @oc_native_cflags@ $(BUILD_MAP_CFLAGS)
 
 # The submodules should be searched *before* any other external -I paths
 OC_INCLUDES = $(addprefix -I $(ROOTDIR)/, \
@@ -104,6 +112,9 @@ OC_DLL_LDFLAGS=@oc_dll_ldflags@
 
 MKEXE_VIA_CC=$(CC) @mkexe_via_cc_ldflags@ @mkexe_via_cc_extra_cmd@
 
+LAUNCH_METHOD = @launch_method@
+SUFFIXING = @suffixing@
+
 # Which tool to use to display differences between files
 DIFF=@DIFF@
 # Which flags to pass to the diff tool
@@ -133,6 +144,10 @@ PACKAGE_TARNAME = @PACKAGE_TARNAME@
 datarootdir = @datarootdir@
 DOCDIR=@docdir@
 
+### Where to look for the standard library on target
+TARGET_LIBDIR=@TARGET_LIBDIR@
+TARGET_LIBDIR_IS_RELATIVE=@target_libdir_is_relative@
+
 unix_directory = @unix_directory@
 unix_library = @unix_library@
 
@@ -171,6 +186,11 @@ OC_NATIVE_COMPFLAGS = @oc_native_compflags@
 
 OC_NATIVE_LINKFLAGS = -g
 
+BUILD_TRIPLET = @build@
+
+# Zinc Runtime ID is needed for installation only
+ZINC_RUNTIME_ID = @zinc_runtime_id@
+
 # Platform-dependent command to create symbolic links
 LN = @ln@
 
@@ -188,3 +208,5 @@ TSAN=@tsan@
 # Contains TSan-specific runtime files, or nothing if TSan support is
 # disabled
 TSAN_NATIVE_RUNTIME_C_SOURCES = @tsan_native_runtime_c_sources@
+
+RUNTIME_SEARCH = @runtime_search@
diff --git a/Makefile.common b/Makefile.common
index 1e6a7eff8903..192daa858f6b 100644
--- a/Makefile.common
+++ b/Makefile.common
@@ -29,6 +29,7 @@ EMPTY :=
 SPACE := $(EMPTY) $(EMPTY)
 # $( ) suppresses warning from the alignments in the V_ macros below
 $(SPACE) :=
+HASH := \#
 
 ifeq "$(UNIX_OR_WIN32)" "win32"
 DIR_SEP := \$ # There must a space following the $
@@ -38,6 +39,8 @@ DIR_SEP = /
 CONVERT_PATH = $(strip $(1))
 endif
 
+QUOTE_SINGLE = '$(subst ','\'',$(1))'
+
 V ?= 0
 
 ifeq "$(V)" "0"
@@ -83,15 +86,351 @@ V_ODOC       =
 endif
 
 DESTDIR ?=
-INSTALL_BINDIR := $(DESTDIR)$(BINDIR)
-INSTALL_LIBDIR := $(DESTDIR)$(LIBDIR)
-INSTALL_INCDIR=$(INSTALL_LIBDIR)/caml
-INSTALL_STUBLIBDIR := $(DESTDIR)$(STUBLIBDIR)
-INSTALL_LIBDIR_PROFILING = $(INSTALL_LIBDIR)/profiling
-INSTALL_MANDIR := $(DESTDIR)$(MANDIR)
-INSTALL_PROGRAMS_MAN_DIR := $(DESTDIR)$(PROGRAMS_MAN_DIR)
-INSTALL_LIBRARIES_MAN_DIR := $(DESTDIR)$(LIBRARIES_MAN_DIR)
-INSTALL_DOCDIR := $(DESTDIR)$(DOCDIR)
+
+# Augment directories from Makefile.config / Makefile.build_config with
+# $(DESTDIR). i.e. each of these 5 directories may be overridden by the user,
+# and the compiler distribution makes no assumptions about where they are
+# relative to each other.
+INSTALL_BINDIR = $(DESTDIR)$(BINDIR)
+INSTALL_DOCDIR = $(DESTDIR)$(DOCDIR)
+INSTALL_LIBDIR = $(DESTDIR)$(LIBDIR)
+INSTALL_MANDIR = $(DESTDIR)$(MANDIR)
+INSTALL_STUBLIBDIR = $(DESTDIR)$(STUBLIBDIR)
+
+# Library subdirectories. The compiler distribution does make assumptions about
+# these, and they cannot be freely overridden by the user.
+INSTALL_LIBDIR_CAML = caml
+INSTALL_LIBDIR_COMPILERLIBS = compiler-libs
+INSTALL_LIBDIR_DYNLINK = dynlink
+INSTALL_LIBDIR_FLEXDLL = flexdll
+INSTALL_LIBDIR_OCAMLDOC = ocamldoc
+INSTALL_LIBDIR_PROFILING = profiling
+INSTALL_LIBDIR_STDLIB = stdlib
+INSTALL_LIBDIR_SYSTHREADS = threads
+
+INSTALL_MANDIR_PROGRAMS = man1
+INSTALL_MANDIR_LIBRARIES = man3
+
+INSTALL_MODE ?= install
+
+# The scripts and commands generated by this installation system allow the user
+# to be installing OCaml to any kind of tortuously difficult path they choose,
+# but it is written assuming that the directory and file names which the
+# distribution is in control of will follow some more restrictive rules, for
+# simplicity.
+# Paths in the installation system should always use forward slashes (these will
+# be automatically translated to backslashes on Windows where required). Both
+# the single and double quote characters are prohibited in all names and paths
+# (this vastly simplifies the quoting assumptions between Unix/Windows). The @
+# symbol is not permitted in directory names because it used internally in
+# filename mangling to represent forward slashes; it is permitted in filenames.
+# Principally owing to escaping limitations of GNU make, it is not possible to
+# use spaces in either source or target file names or in subdirectory names.
+# tools/opam/generate.ml contains some sanity checking on the paths and names
+# generated by these macros - make INSTALL_MODE=clone install is a good
+# confidence check that all rules have been adhered to.
+
+# INSTALL_ITEM installs a single file, possibly with a different name and
+# possibly creating additional symlinks/copies
+#   $1 = source file (may include directories)
+#   $2 = section (bin, doc, lib, libexec, man, stublibs)
+#   $3 = directory within section (may be empty)
+#   $4 = target basename (may be empty)
+#   $5 = additional basenames (either symlinked or copied, depending on what the
+#        platform supports)
+# The $(origin n) dance is necessary to suppress warnings about undefined
+# variables.
+INSTALL_ITEM = \
+  $(INSTALL_$(INSTALL_MODE)_PREFIX)$(call INSTALL_ENSURE_DIR,$\
+    $(strip $(2)),$(if $(filter-out undefined,$(origin 3)),$(strip $(3))))$\
+  $(call INSTALL_DESPATCH_$(INSTALL_MODE)_ITEM,$\
+    $(strip $(1)),$\
+    $(strip $(2)),$\
+    $(if $(filter-out undefined,$(origin 3)),$(strip $(3))),$\
+    $(if $(filter-out undefined,$(origin 4)),$(strip $(4))),$\
+    $(if $(filter-out undefined,$(origin 5)),$(strip $(5))))
+
+# INSTALL_ITEMS installs a series of files to a single directory
+#   $1 = source file(s) (may include directories and glob patterns)
+#   $2 = section (as for INSTALL_ITEM)
+#   $3 = directory within section (may be omitted)
+# INSTALL_ITEMS is sometimes an alias for INSTALL_ITEM. For simplicity with
+# undefined variable warnings, INSTALL_DESPATCH_foo_ITEMS is passed 5 parameters
+# but $4 and $5 are always empty.
+INSTALL_ITEMS = \
+  $(INSTALL_$(INSTALL_MODE)_PREFIX)$(call INSTALL_ENSURE_DIR,$\
+    $(strip $(2)),$(if $(filter-out undefined,$(origin 3)),$(strip $(3))))$\
+  $(call INSTALL_DESPATCH_$(INSTALL_MODE)_ITEMS,$\
+    $(strip $(1)),$\
+    $(strip $(2)),$\
+    $(if $(filter-out undefined,$(origin 3)),$(strip $(3))),,)
+
+# INSTALL_ITEMS_OPT is INSTALL_ITEMS, but does nothing if the source file(s) do
+# not exist
+INSTALL_ITEMS_OPT = \
+  $(if $(wildcard $(1)),$(call INSTALL_ITEMS, \
+    $(1), $(2), $(if $(filter-out undefined,$(origin 3)), $(3))))
+
+INSTALL_ENSURE_DIR = \
+  $(if $(filter undefined,$(origin DIR_CREATED_$(subst exec,,$(1))_$(2))),$\
+    $(eval DIR_CREATED_$(subst exec,,$(1))_$(2):=)$\
+    $(call INSTALL_DESPATCH_$(INSTALL_MODE)_MKDIR,$\
+      $(subst exec,,$(1)),$(2)))
+
+# INSTALL_RM takes a single argument which may include glob patterns of files to
+# be removed when performing a physical install.
+INSTALL_RM = $(call INSTALL_DESPATCH_$(INSTALL_MODE)_RM,$(strip $(1)))
+
+# INSTALL_BEGIN and INSTALL_END are used in the root Makefile's install target
+INSTALL_BEGIN = $(INSTALL_DESPATCH_$(INSTALL_MODE)_BEGIN)
+INSTALL_END = $(INSTALL_DESPATCH_$(INSTALL_MODE)_END)
+
+# Normal installation
+INSTALL_CMD_bin = $(INSTALL_PROG)
+INSTALL_CMD_doc = $(INSTALL_DATA)
+INSTALL_CMD_lib = $(INSTALL_DATA)
+INSTALL_CMD_libexec = $(INSTALL_PROG)
+INSTALL_CMD_man = $(INSTALL_DATA)
+INSTALL_CMD_stublibs = $(INSTALL_PROG)
+
+INSTALL_SECTION_bin = $(INSTALL_BINDIR)
+INSTALL_SECTION_doc = $(INSTALL_DOCDIR)
+INSTALL_SECTION_lib = $(INSTALL_LIBDIR)
+INSTALL_SECTION_libexec = $(INSTALL_LIBDIR)
+INSTALL_SECTION_man = $(INSTALL_MANDIR)
+INSTALL_SECTION_stublibs = $(INSTALL_STUBLIBDIR)
+
+QUOTE_SINGLE = '$(subst ','\'',$(1))'
+
+define NEWLINE
+
+
+endef
+SH_AND = && \$(NEWLINE)
+
+INSTALL_install_PREFIX =
+
+INSTALL_DESPATCH_install_RM = rm -f $(1)
+
+INSTALL_DESPATCH_install_MKDIR = \
+  $(MKDIR) $(call QUOTE_SINGLE,$(INSTALL_SECTION_$(1))$(addprefix /,$(2))) \
+    $(SH_AND)
+
+MK_LINK = \
+  (cd "$(INSTALL_SECTION_$(2))$(addprefix /,$(3))" && \
+    $(LN) $(call QUOTE_SINGLE,$(1)) $(call QUOTE_SINGLE,$(4)))
+
+INSTALL_DESPATCH_install_ITEM = \
+  $(INSTALL_CMD_$(2)) $(1) \
+    $(call QUOTE_SINGLE,$\
+      $(INSTALL_SECTION_$(2))$(addprefix /,$(3))$(addprefix /,$(4))) \
+  $(foreach link, $(5),$(SH_AND)$\
+    $(call MK_LINK,$(if $(4),$(4),$(notdir $(1))),$(2),$(3),$(link)))
+
+INSTALL_DESPATCH_install_ITEMS = $(INSTALL_DESPATCH_install_ITEM)
+
+INSTALL_DESPATCH_install_BEGIN = @
+INSTALL_DESPATCH_install_END = @
+
+INSTALL_display_PREFIX = @
+
+INSTALL_DESPATCH_display_RM = @
+
+INSTALL_DESPATCH_display_MKDIR = \
+  echo $(call QUOTE_SINGLE,$\
+    -> MKDIR $(INSTALL_SECTION_$(1))$(addprefix /,$(2))) $(SH_AND)
+
+MKLINK_display = \
+  echo $(call QUOTE_SINGLE,-> LN \
+         $(abspath $(INSTALL_SECTION_$(2))$(addprefix /,$(3))/$(1)) -> \
+         $(if $(4),$(4),$(notdir $(1))))
+
+INSTALL_DESPATCH_display_ITEM = \
+  echo $(call QUOTE_SINGLE,-> INSTALL $(1) \
+         $(INSTALL_SECTION_$(2))$(addprefix /,$(3))$(addprefix /,$(4))) \
+  $(foreach link, $(5), && \
+    $(call MKLINK_display,$(if $(4),$(4),$(notdir $(1))),$(2),$(3),$(link)))
+
+INSTALL_DESPATCH_display_ITEMS = $(INSTALL_DESPATCH_display_ITEM)
+
+INSTALL_DESPATCH_display_BEGIN = @
+INSTALL_DESPATCH_display_END = @
+
+INSTALL_list_PREFIX = @
+
+INSTALL_DESPATCH_list_RM = @
+
+INSTALL_DESPATCH_list_MKDIR =
+
+MKLINK_list = \
+  echo $(call QUOTE_SINGLE,-> \
+         $(abspath $(INSTALL_SECTION_$(2))$(addprefix /,$(3))/$\
+                     $(if $(4),$(4),$(notdir $(1)))))
+
+INSTALL_DESPATCH_list_ITEM = \
+  echo $(call QUOTE_SINGLE,-> \
+         $(abspath $(INSTALL_SECTION_$(2))$(addprefix /,$(3))/$\
+                     $(if $(4),$(4),$(notdir $(1))))) \
+  $(foreach link, $(5), && \
+    $(call MKLINK_list,$(if $(4),$(4),$(notdir $(1))),$(2),$(3),$(link)))
+
+INSTALL_DESPATCH_list_ITEMS = \
+  $(foreach file, $(wildcard $(1)), \
+    echo $(call QUOTE_SINGLE,-> \
+           $(INSTALL_SECTION_$(2))$(addprefix /,$(3))/$(notdir $(file)));) \
+  true
+
+INSTALL_DESPATCH_list_BEGIN = @
+INSTALL_DESPATCH_list_END = @
+
+OPAM_PACKAGE_NAME ?= ocaml-compiler
+
+# Generate $(OPAM_PACKAGE_NAME).install and $(OPAM_PACKAGE_NAME)-fixup.sh
+#   (INSTALL_MODE=opam)
+# opam's .install format isn't quite rich enough at present to express the
+# installation of the compiler. In particular, we can't install the doc files to
+# doc/ocaml using a .install and we can't create symlinks. The things which
+# can't be handled by the .install file are dealt with by the fixup script
+# instead.
+
+INVOKE = $(strip $(1)) $(call QUOTE_SINGLE,$(strip $(2)))
+ADD_LINE = $(call INVOKE, echo, $(2)) >> $(1)
+
+# RECORD_SYMLINK_TO_INSTALL
+#   $1 = file to install, implicitly relative to $(ROOTDIR)
+#   $2 = section
+#   $3 = subdirectory within $2 (may be empty)
+#   $4 = name to install $1 (must be specified)
+#   $5 = single name of symlink
+# If symlinks are supported, $1 is ignored and the three pieces of information
+# are recorded in create-symlinks: the directory, implicitly relative to the
+# prefix, in which the symlink is to be created, the source file and name of the
+# symlink.
+# These can then be munged to a cd + ln combination in the fixup script.
+# If symlinks are not supported, $1 is instead used to create an additional copy
+# of the file, using the .install file.
+ifeq "$(firstword $(LN))" "ln"
+RECORD_SYMLINK_TO_INSTALL = \
+  $(call ADD_LINE, $(ROOTDIR)/create-symlinks, \
+    $(patsubst lib%,lib,$(2))$(addprefix /,$(3)) $(4) $(5))
+else
+# Symlinks aren't available, so copy the file again using the target name
+RECORD_SYMLINK_TO_INSTALL = \
+  $(call RECORD_$(INSTALL_MODE)_ITEM_TO_INSTALL,$(1),$(2),$(3),$(5))
+endif
+
+# Process the arguments to pass to RECORD_$(INSTALL_MODE)_ITEM_TO_INSTALL:
+# - Items installed to the stublibs section need to be remapped to the stublibs
+#   subdirectory of libexec (since we install to lib/ocaml/stublibs rather than
+#   opam's default lib/stublibs)
+# - Source files must be given implicitly relative to $(ROOTDIR), so prefix with
+#   $(SUBDIR_NAME) if necessary
+# - Items installed to the lib/libexec sections will in fact be installed to
+#   lib_root/libexec_root, so remap the installation directory to ocaml (i.e. to
+#   install to lib/ocaml rather than lib)
+# - If no target basename has been explictly given, use the source's basename
+RECORD_ITEM_TO_INSTALL = \
+  $(if $(filter stublibs,$(2)),\
+    $(call RECORD_ITEM_TO_INSTALL,$\
+      $(1),libexec,stublibs$(addprefix /,$(3)),$(4),$(5)),\
+    $(call RECORD_$(INSTALL_MODE)_ITEM_TO_INSTALL,$\
+      $(addsuffix /,$(SUBDIR_NAME))$(1),$\
+      $(2),$\
+      $(if $(filter doc lib%,$(2)),ocaml$(addprefix /,$(3)),$(3)),$\
+      $(if $(4),$(4),$(notdir $(1))),$\
+      $(5)))
+
+# All files must be explicitly installed, so evaluate the wildcards and call
+# INSTALL_DESPATCH_opam_ITEM for each file.
+INSTALL_EVALUATE_GLOBS = \
+  $(foreach file, $(wildcard $(1)), \
+    $(call INSTALL_DESPATCH_$(INSTALL_MODE)_ITEM,$(file),$(2),$(3));) \
+  true
+
+# RECORD_FILE_TO_INSTALL
+#   $1 = file to install, implicitly relative to $(ROOTDIR)
+#   $2 = bin/lib/libexec/man
+#   $3 = subdirectory within $2 (may be empty, but otherwise must end with "/")
+#   $4 = name to install $1 (must be specified)
+# Writes an opam .install line to the section file for $(2). Each line consists
+# of a double-quoted implicit filename relative to $(ROOTDIR) and optionally a
+# second double-quoted implicit filename relative to the $(2) for the name to
+# install the file under.
+#   e.g. "lex/ocamllex" {"ocamllex.byte"} or "expunge" {"ocaml/expunge"}
+RECORD_FILE_TO_INSTALL = \
+  $(call ADD_LINE, $(ROOTDIR)/opam-$(2), \
+    "$(1)" $(if $(3)$(filter-out $(notdir $(1)),$(4)), {"$(3)$(4)"}))
+
+# RECORD_FILE_TO_CLONE
+#   $1 = file to install, implicitly relative to $(ROOTDIR)
+#   $2 = subdirectory (may be empty, but otherwise must end with "/")
+#   $3 = name to install $1 (must be specified)
+# The compiler is installed as the ocaml package in opam, but the actual files
+# are installed from other packages (typically ocaml-compiler). For the lib
+# directory, the lib_root and libexec_root sections allow files to be installed
+# to lib/ocaml, but there's no equivalent mechanism for the doc directory. These
+# files are recorded to be copied manually in the fixup script.
+RECORD_FILE_TO_CLONE = \
+  $(call ADD_LINE, $(ROOTDIR)/clone-$(subst /,@,$(2)), $(1) $(3))
+
+# RECORD_opam_ITEM_TO_INSTALL despatches the processed arguments of
+# INSTALL_DESPATCH_opam_ITEM to the appropriate RECORD_ macro.
+RECORD_opam_ITEM_TO_INSTALL = \
+  $(if $(filter doc,$(2)),\
+    $(call RECORD_FILE_TO_CLONE,$(1),doc/$(3),$(4)), \
+    $(call RECORD_FILE_TO_INSTALL,$(1),$(2),$(addsuffix /,$(3)),$(4))) \
+  $(foreach link, $(5), && \
+    $(call RECORD_SYMLINK_TO_INSTALL,$(1),$(2),$(3),$(4),$(link)))
+
+INSTALL_DESPATCH_opam_ITEM = $(RECORD_ITEM_TO_INSTALL)
+
+INSTALL_DESPATCH_opam_ITEMS = $(INSTALL_EVALUATE_GLOBS)
+
+INSTALL_opam_PREFIX = @
+
+INSTALL_DESPATCH_opam_RM = @
+
+# INSTALL_MKDIR is ignored (opam creates them when executing the .install file)
+INSTALL_DESPATCH_opam_MKDIR =
+
+INSTALL_DESPATCH_opam_BEGIN = \
+  rm -f opam-bin clone-* opam-lib opam-libexec opam-man create-symlinks
+
+# Munge opam-bin, opam-lib, opam-libexec and opam-man into a .install file and
+# then munge clone-* and create-symlinks into the fixup script.
+INSTALL_DESPATCH_opam_END = \
+  $(OCAMLRUN) ./ocaml$(EXE) $(STDLIBFLAGS) \
+    tools/opam/generate.ml $(INSTALL_MODE) $(OPAM_PACKAGE_NAME) '$(LN)'
+
+# Generate $(OPAM_PACKAGE_NAME)-clone.sh (INSTALL_MODE=clone)
+
+# ld.conf is explicitly copied, rather than cloned, to allow (in principle, if
+# not in practice) the cloning installation to edit it.
+RECORD_clone_ITEM_TO_INSTALL = \
+  $(if $(filter runtime/ld.conf Makefile.config, $(1)), true, \
+    $(if $(filter libexec,$(2)), \
+      $(call RECORD_clone_ITEM_TO_INSTALL,$(1),lib,$(3),$(4),$(5)), \
+      $(call ADD_LINE, \
+        $(ROOTDIR)/clone-$(2)$(addprefix @,$(subst /,@,$(3))), \
+        $(2)$(addprefix /,$(3))/$(if $(4),$(4),$(notdir $(1)))) \
+      $(foreach link, $(5), && \
+        $(call RECORD_SYMLINK_TO_INSTALL,$(1),$(2),$(3),$(4),$(link)))))
+
+INSTALL_DESPATCH_clone_ITEM = $(RECORD_ITEM_TO_INSTALL)
+
+INSTALL_DESPATCH_clone_ITEMS = $(INSTALL_EVALUATE_GLOBS)
+
+INSTALL_clone_PREFIX = @
+
+INSTALL_DESPATCH_clone_RM = @
+
+# INSTALL_MKDIR is ignored - INSTALL_DESPATCH_clone_END automatically creates
+# directories for each cp file.
+INSTALL_DESPATCH_clone_MKDIR =
+
+INSTALL_DESPATCH_clone_BEGIN = rm -f clone-* create-symlinks
+
+INSTALL_DESPATCH_clone_END = $(INSTALL_DESPATCH_opam_END)
 
 FLEXDLL_SUBMODULE_PRESENT := $(wildcard $(ROOTDIR)/flexdll/Makefile)
 
@@ -141,9 +480,29 @@ ifeq "$(BOOTSTRAPPING_FLEXDLL)" "true"
 ifeq "$(filter $(REAL_ROOT_DIR)/$(BYTE_BINDIR), $(subst :, ,$(PATH)))" ""
   export PATH := \
     $(REAL_ROOT_DIR)/$(OPT_BINDIR):$(REAL_ROOT_DIR)/$(BYTE_BINDIR):$(PATH)
+  # $(BUILD_COMPANY_SYSTEM) is the last two parts of $(BUILD_TRIPLET)
+  BUILD_TRIPLET_FIELDS := $(subst -,$(SPACE),$(BUILD_TRIPLET))
+  BUILD_COMPANY_SYSTEM := $(subst $(SPACE),-,$\
+    $(wordlist 2, $(words $(BUILD_TRIPLET_FIELDS)), $(BUILD_TRIPLET_FIELDS)))
+  # Use the FLEXDIR environment variable to tell flexlink where the support
+  # objects are located. Passing this location using -I would defeat the whole
+  # purpose of the PATH-trick (bootstrapped flexlink is indistinguishable from
+  # an installed flexlink). flexlink also looks for the objects in the same
+  # directory as the executable, but this is slightly irritating as it requires
+  # copying them to both byte/bin/ and opt/bin/ but also doesn't work if
+  # opt/bin/flexlink.exe is a symlink to flexlink.opt.exe, as flexlink can end
+  # up looking in the directory for the target of the symlink, rather than the
+  # symlink itself.
+ifeq "" "$(filter pc-msys pc-cygwin%, $(BUILD_COMPANY_SYSTEM))"
+  export FLEXDIR := $(REAL_ROOT_DIR)
+else
+  export FLEXDIR := $(shell cygpath -w "$(REAL_ROOT_DIR)")
 endif
-  undefine REAL_ROOT_DIR
+  undefine BUILD_TRIPLET_FIELDS
+  undefine BUILD_COMPANY_SYSTEM
 endif
+  undefine REAL_ROOT_DIR
+endif # ifeq "$(BOOTSTRAPPING_FLEXDLL)" "true"
 
 # List of other libraries
 ALL_OTHERLIBS = dynlink str systhreads unix runtime_events
@@ -156,6 +515,22 @@ ifeq "$(FUNCTION_SECTIONS)" "true"
 OPTCOMPFLAGS += -function-sections
 endif
 
+ifeq "$(TARGET_LIBDIR_IS_RELATIVE)" "true"
+  SRCDIR_ENCODED = $(subst =,%+,$(subst :,%.,$(subst %,%$(HASH),$(SRCDIR_ABS))))
+  SRCDIR_ABS_REAL := $(shell realpath $(SRCDIR_ABS) 2>/dev/null)
+  SRCDIR_REAL_ENCODED = \
+    $(subst =,%+,$(subst :,%.,$(subst %,%$(HASH),$(SRCDIR_ABS_REAL))))
+  BUILD_PATH_PREFIX_MAP ?=
+  export BUILD_PATH_PREFIX_MAP := \
+    $(BUILD_PATH_PREFIX_MAP)$\
+      :.=$(SRCDIR_ENCODED)$\
+      $(if $(SRCDIR_REAL_ENCODED),:.=$(SRCDIR_REAL_ENCODED))
+endif # ifeq "$(TARGET_LIBDIR_IS_RELATIVE)" "true"
+
+OC_COMMON_LINKFLAGS += \
+  -set-runtime-default \
+    $(call QUOTE_SINGLE,standard_library_default=$(TARGET_LIBDIR))
+
 # The rule to compile C files
 
 # This rule is similar to GNU make's implicit rule, except that it is more
@@ -301,8 +676,20 @@ $(eval $(call _OCAML_COMMON_BASE,$(1)))
 $(basename $(notdir $(1)))_COMMON_LINKFLAGS =
 endef # _OCAML_PROGRAM_BASE
 
+# $(ROOTDIR)/ocamlc needs -launch-method to be given explicitly as its default
+# values are those for the target (cf. --with-target-sh and TARGET_BINDIR).
+BYTECODE_LAUNCHER_FLAGS = \
+  -launch-method $(call QUOTE_SINGLE,$(LAUNCH_METHOD) $(BINDIR)) \
+  -runtime-search $(if $(RUNTIME_SEARCH),$(RUNTIME_SEARCH),disable)
+
+MAYBE_ADD_BYTECODE_LAUNCHER_FLAGS = \
+  $(if $(filter -custom, $(1)),,\
+    -use-prims $(ROOTDIR)/runtime/primitives $(BYTECODE_LAUNCHER_FLAGS))
+
 LINK_BYTECODE_PROGRAM =\
-  $(CAMLC) $(OC_COMMON_LINKFLAGS) $(OC_BYTECODE_LINKFLAGS)
+  $(CAMLC) $(OC_COMMON_LINKFLAGS) \
+    $(call MAYBE_ADD_BYTECODE_LAUNCHER_FLAGS, \
+      $(OC_COMMON_LINKFLAGS) $(OC_BYTECODE_LINKFLAGS)) $(OC_BYTECODE_LINKFLAGS)
 
 # The _OCAML_BYTECODE_PROGRAM macro defines a bytecode program but assuming
 # that _OCAML_PROGRAM_BASE has already been called. Its public counterpart
@@ -326,8 +713,12 @@ $(basename $(notdir $(1)))_BYTECODE_LINKFLAGS =
 
 $(basename $(notdir $(1)))_BYTECODE_LINKCMD = \
 $(strip \
-  $$(CAMLC) $$(OC_COMMON_LINKFLAGS) $$(OC_BYTECODE_LINKFLAGS) \
-  $$($(basename $(notdir $(1)))_COMMON_LINKFLAGS) \
+  $$(CAMLC) $$(OC_COMMON_LINKFLAGS) \
+  $$(call MAYBE_ADD_BYTECODE_LAUNCHER_FLAGS, \
+    $$(OC_COMMON_LINKFLAGS) $$(OC_BYTECODE_LINKFLAGS) \
+    $$($(basename $(notdir $(1)))_COMMON_LINKFLAGS) \
+    $$($(basename $(notdir $(1)))_BYTECODE_LINKFLAGS)) \
+  $$(OC_BYTECODE_LINKFLAGS) $$($(basename $(notdir $(1)))_COMMON_LINKFLAGS) \
   $$($(basename $(notdir $(1)))_BYTECODE_LINKFLAGS))
 
 $(1)$(EXE): $$$$($(basename $(notdir $(1)))_BCOBJS)
@@ -453,12 +844,11 @@ $(eval $(call _OCAML_BYTECODE_LIBRARY,$(1)))
 $(eval $(call _OCAML_NATIVE_LIBRARY,$(1)))
 endef # OCAML_LIBRARY
 
-# Installing a bytecode executable, with debug information removed
-define INSTALL_STRIPPED_BYTE_PROG
-$(OCAMLRUN) $(ROOTDIR)/tools/stripdebug $(1) $(1).tmp \
-&& $(INSTALL_PROG) $(1).tmp $(2) \
-&& rm $(1).tmp
-endef # INSTALL_STRIPPED_BYTE_PROG
+# Strip debug information from a bytecode executable
+define STRIP_BYTE_PROG
+$(OCAMLRUN) $(ROOTDIR)/tools/stripdebug$(EXE) \
+  $(strip $(1)) $(strip $(1)).stripped
+endef # STRIP_BYTE_PROG
 
 # ocamlc has several mechanisms for linking a bytecode image to the runtime
 # which executes it. The exact mechanism depends on the platform and the precise
@@ -467,3 +857,20 @@ endef # INSTALL_STRIPPED_BYTE_PROG
 # boot/ as part of coldstart. See read_runtime_launch_info in
 # bytecomp/bytelink.ml for further details.
 HEADER_NAME = runtime-launch-info
+
+ifeq "$(UNIX_OR_WIN32)" "win32"
+# Ensure that no command can create Cygwin symbolic links by ensuring that
+# symlink(2) will fail if native NTFS symlinks aren't available.
+CYGWIN ?=
+MSYS ?=
+export CYGWIN := $(strip \
+  $(filter-out winsymlinks winsymlinks:%, $(CYGWIN)) winsymlinks:nativestrict)
+export MSYS := $(strip \
+  $(filter-out winsymlinks winsymlinks:%, $(MSYS)) winsymlinks:nativestrict)
+endif
+
+# Invocations of the compilers during the build use -nostdlib which ensures that
+# existing installations and the OCAMLLIB/CAMLLIB environment variables don't
+# affect the build. There isn't an equivalent flag for the toplevel's
+# OCAMLTOP_INCLUDE_PATH, so it's scrubbed from the environment instead.
+unexport OCAMLTOP_INCLUDE_PATH
diff --git a/Makefile.config.in b/Makefile.config.in
index e432851cdea5..10b6917ada44 100644
--- a/Makefile.config.in
+++ b/Makefile.config.in
@@ -219,6 +219,10 @@ FUNCTION_SECTIONS=@function_sections@
 AWK=@AWK@
 NAKED_POINTERS=false
 
+# Runtime ID values
+BYTECODE_RUNTIME_ID=@bytecode_runtime_id@
+NATIVE_RUNTIME_ID=@native_runtime_id@
+
 # Deprecated variables
 
 ## Variables deprecated since OCaml 5.3
diff --git a/VERSION b/VERSION
index b562d9f5108f..65b318906844 100644
--- a/VERSION
+++ b/VERSION
@@ -1,4 +1,4 @@
-5.3.1+dev0-2025-01-06
+5.3.1+relocatable
 
 # Starting with OCaml 4.14, although the version string that appears above is
 # still correct and this file can thus still be used to figure it out,
diff --git a/aclocal.m4 b/aclocal.m4
index 7353e09a96ef..791a49432ed5 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -543,3 +543,14 @@ AC_DEFUN([OCAML_CC_SUPPORTS_LABELS_AS_VALUES], [
       [Define if the C compiler supports the labels as values extension.])
   fi
 ])
+
+AC_DEFUN([OCAML_CHECK_LN_ON_WINDOWS], [
+  AC_MSG_CHECKING([for a workable solution for ln -sf])
+  AS_IF([m4_normalize(MSYS=winsymlinks:nativestrict
+                      CYGWIN=winsymlinks:nativestrict
+                      ln -sf configure conftestLink 2>/dev/null)],
+    [ln='ln -sf'],
+    [ln='cp -pf']
+  )
+  AC_MSG_RESULT([$ln])
+])
diff --git a/api_docgen/Makefile b/api_docgen/Makefile
index 07254645812a..4ad898ea6bfd 100644
--- a/api_docgen/Makefile
+++ b/api_docgen/Makefile
@@ -14,6 +14,7 @@
 #**************************************************************************
 # Used by included Makefiles
 ROOTDIR = ..
+SUBDIR_NAME = api_docgen
 -include ../Makefile.build_config
 
 odoc-%:
diff --git a/api_docgen/ocamldoc/Makefile b/api_docgen/ocamldoc/Makefile
index 5b1f8946d802..a9781f1aba2d 100644
--- a/api_docgen/ocamldoc/Makefile
+++ b/api_docgen/ocamldoc/Makefile
@@ -14,6 +14,7 @@
 #**************************************************************************
 # Used by included Makefiles
 ROOTDIR = ../..
+SUBDIR_NAME = api_docgen/ocamldoc
 include ../Makefile.common
 vpath %.mli ../../stdlib $(DOC_COMPILERLIBS_DIRS)  $(DOC_STDLIB_DIRS)
 
@@ -120,7 +121,4 @@ build/latex/compilerlibs_input.tex: | build/latex
 
 .PHONY: install
 install:
-	$(MKDIR) "$(INSTALL_LIBRARIES_MAN_DIR)"
-	if test -d build/man; then \
-	  $(INSTALL_DATA) build/man/*.3o "$(INSTALL_LIBRARIES_MAN_DIR)"; \
-	fi
+	$(call INSTALL_ITEMS_OPT, build/man/*.3o, man, $(INSTALL_MANDIR_LIBRARIES))
diff --git a/api_docgen/odoc/Makefile b/api_docgen/odoc/Makefile
index c40ed778c41e..8f2c0195571a 100644
--- a/api_docgen/odoc/Makefile
+++ b/api_docgen/odoc/Makefile
@@ -15,6 +15,7 @@
 
 # Used by included Makefiles
 ROOTDIR = ../..
+SUBDIR_NAME = api_docgen/odoc
 
 include ../Makefile.common
 
@@ -191,13 +192,10 @@ $(ALL_PAGED_DOC:%=build/%.3o.stamp):build/%.3o.stamp:build/%.odocl | build/
 # Man pages are the only installed documentation
 .PHONY: install
 install:
-	$(MKDIR) "$(INSTALL_LIBRARIES_MAN_DIR)"
-	if test -d build/man/libref ; then \
-	  $(INSTALL_DATA) build/man/libref/* "$(INSTALL_LIBRARIES_MAN_DIR)"; \
-	fi
-	if test -d build/man/compilerlibref ; then \
-	  $(INSTALL_DATA) build/man/libref/* "$(INSTALL_LIBRARIES_MAN_DIR)"; \
-	fi
+	$(call INSTALL_ITEMS_OPT, \
+	  build/man/libref/*, man, $(INSTALL_MANDIR_LIBRARIES))
+	$(call INSTALL_ITEMS_OPT, \
+	  build/man/compilerlibref/*, man, $(INSTALL_MANDIR_LIBRARIES))
 
 # Dependencies for stdlib modules.
 # Use the same dependencies used for compiling .cmx files.
diff --git a/appveyor.yml b/appveyor.yml
index ad1426d9bc1b..201a7a363586 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -44,6 +44,7 @@ environment:
   matrix:
     - PORT: mingw64
       BOOTSTRAP_FLEXDLL: true
+      RELOCATABLE: true
 # OCaml 5.0 does not yet support MSVC
 #    - PORT: msvc64
 #      BOOTSTRAP_FLEXDLL: false
diff --git a/asmcomp/asmlink.ml b/asmcomp/asmlink.ml
index e8179a729f7c..060ae7ac4f3c 100644
--- a/asmcomp/asmlink.ml
+++ b/asmcomp/asmlink.ml
@@ -105,12 +105,18 @@ let add_ccobjs origin l =
   end
 
 let runtime_lib () =
-  let libname = "libasmrun" ^ !Clflags.runtime_variant ^ ext_lib in
-  try
-    if !Clflags.nopervasives || not !Clflags.with_runtime then []
-    else [ Load_path.find libname ]
-  with Not_found ->
-    raise(Error(File_not_found libname))
+  if !Clflags.runtime_variant = "_shared" then
+    if Config.suffixing then
+      [Misc.RuntimeID.shared_runtime Sys.Native]
+    else
+      ["-lasmrun_shared"]
+  else
+    let libname = "libasmrun" ^ !Clflags.runtime_variant ^ ext_lib in
+    try
+      if !Clflags.nopervasives || not !Clflags.with_runtime then []
+      else [ Load_path.find libname ]
+    with Not_found ->
+      raise(Error(File_not_found libname))
 
 (* First pass: determine which units are needed *)
 
@@ -198,6 +204,10 @@ let make_globals_map units_list ~crc_interfaces =
     crc_interfaces defined
 
 let make_startup_file ~ppf_dump units_list ~crc_interfaces =
+  let need_stdlib =
+    let needs_stdlib (ui, _, _) = Compilenv.needs_stdlib_location ui in
+    List.exists needs_stdlib units_list
+  in
   let compile_phrase p = Asmgen.compile_phrase ~ppf_dump p in
   Location.input_name := "caml_startup"; (* set name of "current" input *)
   Compilenv.reset "_startup";
@@ -224,6 +234,14 @@ let make_startup_file ~ppf_dump units_list ~crc_interfaces =
   Array.iteri
     (fun i name -> compile_phrase (Cmm_helpers.predef_exception i name))
     Runtimedef.builtin_exceptions;
+  if need_stdlib then begin
+    let standard_library_default =
+      Option.value ~default:Config.standard_library_default
+                   !Clflags.standard_library_default in
+    compile_phrase
+      (Cdata (Cmm_helpers.emit_string_constant
+        ("caml_standard_library_nat", Global) standard_library_default []))
+  end;
   compile_phrase (Cmm_helpers.global_table name_list);
   let globals_map = make_globals_map units_list ~crc_interfaces in
   compile_phrase (Cmm_helpers.globals_map globals_map);
diff --git a/asmcomp/asmpackager.ml b/asmcomp/asmpackager.ml
index f0e2148f447c..3745eb0d61f6 100644
--- a/asmcomp/asmpackager.ml
+++ b/asmcomp/asmpackager.ml
@@ -217,6 +217,7 @@ let build_package_cmx members cmxfile =
     else
       Clambda (get_approx ui)
   in
+  let ui_need_stdlib = List.exists Compilenv.needs_stdlib_location units in
   Export_info_for_pack.clear_import_state ();
   let pkg_infos =
     { ui_name = ui.ui_name;
@@ -238,9 +239,9 @@ let build_package_cmx members cmxfile =
       ui_force_link =
           List.exists (fun info -> info.ui_force_link) units;
       ui_export_info;
-      ui_for_pack = None;
+      ui_for_pack = None
     } in
-  Compilenv.write_unit_info pkg_infos cmxfile
+  Compilenv.write_unit_info ~ui_need_stdlib pkg_infos cmxfile
 
 (* Make the .cmx and the .o for the package *)
 
diff --git a/boot/ocamlc b/boot/ocamlc
index 852a0ec90168..e93db9ae174f 100755
Binary files a/boot/ocamlc and b/boot/ocamlc differ
diff --git a/boot/ocamllex b/boot/ocamllex
index 1c1de472dd66..e725ca13139a 100755
Binary files a/boot/ocamllex and b/boot/ocamllex differ
diff --git a/build-aux/ocaml_version.m4 b/build-aux/ocaml_version.m4
index 4079bf3bca87..e689cf8ca302 100644
--- a/build-aux/ocaml_version.m4
+++ b/build-aux/ocaml_version.m4
@@ -29,14 +29,17 @@ m4_define([OCAML__DEVELOPMENT_VERSION], [true])
 
 # The three following components (major, minor and patch level) MUST be
 # integers. They MUST NOT be left-padded with zeros and all of them,
-# including the patchlevel, are mandatory.
+# including the patchlevel, are mandatory. OCAML__RELEASE_NUMBER must be
+# incremented with each minor release, and likewise must be an unpadded integer.
 
 m4_define([OCAML__VERSION_MAJOR], [5])
 m4_define([OCAML__VERSION_MINOR], [3])
+m4_define([OCAML__RELEASE_NUMBER], [19])
 m4_define([OCAML__VERSION_PATCHLEVEL], [1])
+
 # Note that the OCAML__VERSION_EXTRA string defined below is always empty
 # for officially-released versions of OCaml.
-m4_define([OCAML__VERSION_EXTRA], [dev0-2025-01-06])
+m4_define([OCAML__VERSION_EXTRA], [relocatable])
 
 # The OCAML__VERSION_EXTRA_PREFIX macro defined below should be a
 # single character:
diff --git a/bytecomp/bytegen.ml b/bytecomp/bytegen.ml
index 4665ac84bcac..ef054c2c9be4 100644
--- a/bytecomp/bytegen.ml
+++ b/bytecomp/bytegen.ml
@@ -439,7 +439,8 @@ let comp_primitive stack_info p sz args =
        | Ostype_unix -> "ostype_unix"
        | Ostype_win32 -> "ostype_win32"
        | Ostype_cygwin -> "ostype_cygwin"
-       | Backend_type -> "backend_type" in
+       | Backend_type -> "backend_type"
+       | Standard_library_default -> "standard_library_default" in
      Kccall(Printf.sprintf "caml_sys_const_%s" const_name, 1)
   | Pisint -> Kisint
   | Pisout -> Kisout
diff --git a/bytecomp/bytelibrarian.ml b/bytecomp/bytelibrarian.ml
index 4ff25d2f4c48..138de8a24ccf 100644
--- a/bytecomp/bytelibrarian.ml
+++ b/bytecomp/bytelibrarian.ml
@@ -48,12 +48,12 @@ let lib_dllibs = ref []
    Notice that here we scan .cma files given on the command line from
    left to right, hence options must be added after. *)
 
-let add_ccobjs l =
+let add_ccobjs l dllibs =
   if not !Clflags.no_auto_link then begin
     if l.lib_custom then Clflags.custom_runtime := true;
     lib_ccobjs := !lib_ccobjs @ l.lib_ccobjs;
     lib_ccopts := !lib_ccopts @ l.lib_ccopts;
-    lib_dllibs := !lib_dllibs @ l.lib_dllibs
+    lib_dllibs := !lib_dllibs @ dllibs
   end
 
 let copy_object_file oc name =
@@ -79,7 +79,7 @@ let copy_object_file oc name =
       seek_in ic toc_pos;
       let toc = (input_value ic : library) in
       List.iter (Bytelink.check_consistency file_name) toc.lib_units;
-      add_ccobjs toc;
+      add_ccobjs toc (Dll.read_suffixed_dllibs_from_channel ic toc);
       List.iter (copy_compunit ic oc) toc.lib_units;
       close_in ic;
       List.map (fun u -> name, u) toc.lib_units
@@ -107,16 +107,30 @@ let create_archive file_list lib_name =
        (match Linkdeps.check ldeps with
         | None -> ()
         | Some e -> raise (Error (Link_error e)));
+       let suffixed, lib_dllibs =
+         let f (suffixed, l) (a, b) = (suffixed::a, l::b) in
+         List.fold_right f (!Clflags.dllibs @ !lib_dllibs) ([], [])
+       in
        let toc =
          { lib_units = (List.map snd units);
            lib_custom = !Clflags.custom_runtime;
            lib_ccobjs = !Clflags.ccobjs @ !lib_ccobjs;
            lib_ccopts = !Clflags.all_ccopts @ !lib_ccopts;
-           lib_dllibs = !Clflags.dllibs @ !lib_dllibs } in
+           lib_dllibs } in
        let pos_toc = pos_out outchan in
        Emitcode.marshal_to_channel_with_possibly_32bit_compat
          ~filename:lib_name ~kind:"bytecode library"
          outchan toc;
+       (* If lib_dllibs is empty or none of the entries had suffixed:true then
+          there's no need to write the suffixed list. Otherwise, output the
+          reverse cma magic number again and then the suffixed list to be
+          List.combine'd with lib_dllibs when the library is unmarshalled. *)
+       if List.mem true suffixed then begin
+         for i = String.length cma_magic_number - 1 downto 0 do
+           output_char outchan Config.cma_magic_number.[i]
+         done;
+         output_value outchan suffixed
+       end;
        seek_out outchan ofs_pos_toc;
        output_binary_int outchan pos_toc;
     )
diff --git a/bytecomp/bytelink.ml b/bytecomp/bytelink.ml
index db4fa18e76ce..dbc93c0e8b33 100644
--- a/bytecomp/bytelink.ml
+++ b/bytecomp/bytelink.ml
@@ -55,7 +55,7 @@ let lib_ccobjs = ref []
 let lib_ccopts = ref []
 let lib_dllibs = ref []
 
-let add_ccobjs origin l =
+let add_ccobjs origin l dllibs =
   if not !Clflags.no_auto_link then begin
     if
       String.length !Clflags.use_runtime = 0
@@ -68,7 +68,7 @@ let add_ccobjs origin l =
       in
       lib_ccopts := List.map replace_origin l.lib_ccopts @ !lib_ccopts;
     end;
-    lib_dllibs := l.lib_dllibs @ !lib_dllibs
+    lib_dllibs := dllibs @ !lib_dllibs
   end
 
 (* A note on ccobj ordering:
@@ -139,8 +139,9 @@ let scan_file ldeps obj_name tolink =
       let pos_toc = input_binary_int ic in    (* Go to table of contents *)
       seek_in ic pos_toc;
       let toc = (input_value ic : library) in
+      let dllibs = Dll.read_suffixed_dllibs_from_channel ic toc in
       close_in ic;
-      add_ccobjs (Filename.dirname file_name) toc;
+      add_ccobjs (Filename.dirname file_name) toc dllibs;
       let required =
         List.fold_right
           (fun compunit reqd ->
@@ -199,7 +200,7 @@ let debug_info = ref ([] : (int * Instruct.debug_event list * string list) list)
 
 (* Link in a compilation unit *)
 
-let link_compunit output_fun currpos_fun inchan file_name compunit =
+let link_compunit accu output_fun currpos_fun inchan file_name compunit =
   check_consistency file_name compunit;
   seek_in inchan compunit.cu_pos;
   let code_block =
@@ -225,46 +226,44 @@ let link_compunit output_fun currpos_fun inchan file_name compunit =
     debug_info := (currpos_fun(), debug_event_list, debug_dirs) :: !debug_info
   end;
   output_fun code_block;
-  if !Clflags.link_everything then
-    List.iter Symtable.require_primitive compunit.cu_primitives
+  let fold_primitive needs_stdlib name =
+    if !Clflags.link_everything then
+      Symtable.require_primitive name;
+    (needs_stdlib || name = "%standard_library_default")
+  in
+  List.fold_left fold_primitive accu compunit.cu_primitives
 
 (* Link in a .cmo file *)
 
-let link_object output_fun currpos_fun file_name compunit =
-  let inchan = open_in_bin file_name in
-  try
-    link_compunit output_fun currpos_fun inchan file_name compunit;
-    close_in inchan
-  with
-    Symtable.Error msg ->
-      close_in inchan; raise(Error(Symbol_error(file_name, msg)))
-  | x ->
-      close_in inchan; raise x
+let link_object accu output_fun currpos_fun file_name compunit =
+  In_channel.with_open_bin file_name @@ fun inchan ->
+    try link_compunit accu output_fun currpos_fun inchan file_name compunit
+    with Symtable.Error msg -> raise(Error(Symbol_error(file_name, msg)))
 
 (* Link in a .cma file *)
 
-let link_archive output_fun currpos_fun file_name units_required =
-  let inchan = open_in_bin file_name in
-  try
-    List.iter
-      (fun cu ->
+let link_archive accu output_fun currpos_fun file_name units_required =
+  In_channel.with_open_bin file_name @@ fun inchan ->
+    List.fold_left
+      (fun accu cu ->
          let n = Compunit.name cu.cu_name in
          let name = file_name ^ "(" ^ n ^ ")" in
          try
-           link_compunit output_fun currpos_fun inchan name cu
+           link_compunit accu output_fun currpos_fun inchan name cu
          with Symtable.Error msg ->
            raise(Error(Symbol_error(name, msg))))
-      units_required;
-    close_in inchan
-  with x -> close_in inchan; raise x
+      accu units_required
 
 (* Link in a .cmo or .cma file *)
 
-let link_file output_fun currpos_fun = function
+let link_file output_fun currpos_fun accu = function
     Link_object(file_name, unit) ->
-      link_object output_fun currpos_fun file_name unit
+      link_object accu output_fun currpos_fun file_name unit
   | Link_archive(file_name, units) ->
-      link_archive output_fun currpos_fun file_name units
+      link_archive accu output_fun currpos_fun file_name units
+
+let link_files output_fun currpos_fun =
+  List.fold_left (link_file output_fun currpos_fun) false
 
 (* Output the debugging information *)
 (* Format is:
@@ -297,13 +296,6 @@ type launch_method =
 | Shebang_runtime
 | Executable
 
-type runtime_launch_info = {
-  buffer : string;
-  bindir : string;
-  launcher : launch_method;
-  executable_offset : int
-}
-
 (* See https://www.in-ulm.de/~mascheck/various/shebang/#origin for a deep
    dive into shebangs.
    - Whitespace (space or horizontal tab) delimits the interpreter from an
@@ -316,60 +308,23 @@ let invalid_for_shebang_line path =
   let invalid_char = function ' ' | '\t' | '\n' -> true | _ -> false in
   String.length path > 125 || String.exists invalid_char path
 
-(* The runtime-launch-info file consists of two "lines" followed by binary data.
-   The file is _always_ LF-formatted, even on Windows. The sequence of bytes up
-   to the first '\n' is interpreted:
-     - "sh" - use a shebang-style launcher. If sh is needed, determine its
-              location from [command -p -v sh]
-     - "exe" - use the executable launcher contained in this runtime-launch-info
-               file.
-     - "/" ^ path - use a shebang-style launcher. If sh is needed, path is the
-                    absolute location of sh. path must be valid for a shebang
-                    line.
-   The second "line" is interpreted as the next "\000\n"-terminated sequence and
-   is the directory containing the default runtimes (ocamlrun, ocamlrund, etc.).
-   The null terminator is used since '\n' is valid in a nefarious installation
-   prefix but Posix forbids filenames including the nul character.
-   The remainder of the file is then the executable launcher for bytecode
-   programs (see stdlib/header{,nt}.c). *)
-
-let read_runtime_launch_info file =
-  let buffer =
-    try
-      In_channel.with_open_bin file In_channel.input_all
-    with Sys_error msg -> raise (Error (Camlheader (msg, file)))
-  in
-  try
-    let bindir_start = String.index buffer '\n' + 1 in
-    let bindir_end = String.index_from buffer bindir_start '\000' in
-    let bindir = String.sub buffer bindir_start (bindir_end - bindir_start) in
-    let executable_offset = bindir_end + 2 in
-    let launcher =
-      let kind = String.sub buffer 0 (bindir_start - 1) in
-      if kind = "exe" then
-        Executable
-      else if kind <> "" && (kind.[0] = '/' || kind = "sh") then
-        Shebang_bin_sh kind
-      else
-        raise Not_found in
-    if String.length buffer < executable_offset
-       || buffer.[executable_offset - 1] <> '\n' then
-      raise Not_found
-    else
-      {bindir; launcher; buffer; executable_offset}
-  with Not_found ->
-    raise (Error (Camlheader ("corrupt header", file)))
-
 let find_bin_sh () =
   let output_file = Filename.temp_file "caml_bin_sh" "" in
   let result =
   try
-    let cmd =
-      Filename.quote_command ~stdout:output_file "command" ["-p"; "-v"; "sh"]
+    let run command args =
+      let cmd =
+        Filename.quote_command ~stdout:output_file command args
+      in
+      if !Clflags.verbose then
+        Printf.eprintf "+ %s\n" cmd;
+      (Sys.command cmd = 0)
     in
-    if !Clflags.verbose then
-      Printf.eprintf "+ %s\n" cmd;
-    if Sys.command cmd = 0 then
+    (* While [command -v] and [command -p] are long-standing Posix commands,
+       the ability to combine them as [command -p -v] is actually Posix Issue 7
+       and so of course Solaris does not support it *)
+    if run "command" ["-p"; "-v"; "sh"] ||
+       run "sh" ["-c"; "PATH=\"`getconf PATH`\" command -v sh"] then
       In_channel.with_open_text output_file input_line
     else
       ""
@@ -379,75 +334,189 @@ let find_bin_sh () =
   remove_file output_file;
   result
 
+(* Writes the shell script version of the bytecode launcher to outchan *)
+let write_sh_launcher outchan bin_sh bindir search runtime =
+  let open struct type tag = DFE | F | FE end in
+  let l tag fmt =
+    let output s =
+      match tag, search with
+      | DFE, _
+      | F, Config.Fallback
+      | FE, (Config.Fallback | Config.Enable) ->
+          output_string outchan (String.trim s);
+          output_char outchan '\n'
+      | _ ->
+          ()
+    in
+    Printf.ksprintf output fmt
+  in
+  let runtime = Filename.quote runtime in
+  let bin = Filename.quote (Filename.concat bindir "") in
+  let exec =
+    if search = Config.Disable then
+      runtime
+    else
+      {|"$c"|}
+  in
+  let release =
+    Printf.sprintf "%d.%d" Sys.ocaml_release.major Sys.ocaml_release.minor
+  in
+  (* Each of the three search modes requires a slightly different shell script.
+     However, these shell scripts do have one very useful property: the script
+     for Fallback adds lines to the script for Enable which adds lines to the
+     script for Disable, but none of them change lines (apart from a trivial
+     tweak to the exec line for the Disable script).
+     The lines below are laid out to reflect this, with the tag letters
+     D(isable), F(allback) and E(nable) for the lines in each script. If a line
+     is emitted, it is first passed to String.trim, which allows indentation and
+     a column-based layout to be used.
+
+     The Disable script just needs to exec the runtime. The two searching modes
+     do a few more calculations and will ultimately exec the contents of $c
+     (which is why exec_arg above is set to the literal string {v "$c" v}).
+
+     In the script itself:
+     - $r is the name of the runtime ('ocamlrun', 'ocamlrund', etc.)
+     - $d is calculated in the script as $(dirname "$0") - i.e. the directory
+       containing the bytecode executable itself
+     - $c will ultimately be the runtime to exec. If it is empty, then the
+       script displays an error message. For Fallback, $c will be the first
+       runtime to try (i.e. the runtime in bindir), and the bindir passed must
+       end with a separator (which is ensured by Filename.concat above)
+
+     The script tries up to three options:
+     - exec $c, if it exists (prefer the runtime in bindir)
+     - exec $d/$r, if it exists (prefer a runtime in the same directory
+       as the bytecode executable)
+     - otherwise try $(command -v "$r") (search PATH for the runtime)
+
+     If the script fails to find an interpreter, $c will always be empty
+       (since [command -v] will have returned an empty string) and an
+       error message can be displayed. *)
+  l DFE {|#!%s                                                     |} bin_sh;
+  l  FE {|r=%s                                                     |} runtime;
+  l  F  {|c=%s"$r"                                                 |} bin;
+  l  F  {|if ! test -f "$c"; then                                  |};
+  l  FE {|  d="$(dirname "$0" 2>/dev/null)"                        |};
+  l  FE {|  test -z "$d" || d="${d%%/}/"                           |};
+  l  FE {|  c="$(command -v "$d$r")"                               |};
+  l  FE {|  test -n "$c" || c="$(command -v "$r")"                 |};
+  l  F  {|fi                                                       |};
+  l  FE {|if test -z "$c"; then                                    |};
+  l  FE {|  echo 'This program requires an OCaml %s interpreter'>&2|} release;
+  l  FE {|  echo "$r not found either alongside $0 or in \$PATH">&2|};
+  l  FE {|else                                                     |};
+  l DFE {|  exec %s "$0" "$@"                                      |} exec;
+  l  FE {|fi                                                       |};
+  l  FE {|exit 126                                                 |}
+
 (* Writes the executable header to outchan and writes the RNTM section, if
    needed. Returns a toc_writer (i.e. Bytesections.init_record is always
    called) *)
 
 let write_header outchan =
-  let use_runtime, runtime =
-    if String.length !Clflags.use_runtime > 0 then
-      (true, make_absolute !Clflags.use_runtime)
-    else
-      (false, "ocamlrun" ^ !Clflags.runtime_variant)
-  in
-  (* Write the header *)
-  let runtime_info =
-    let header = "runtime-launch-info" in
-    try read_runtime_launch_info (Load_path.find header)
-    with Not_found -> raise (Error (File_not_found header))
+  let zinc_runtime_id, write_exe_launcher =
+    let header =
+      let header = "runtime-launch-info" in
+      try Load_path.find header
+      with Not_found -> raise (Error (File_not_found header))
+    in
+    let data =
+      try In_channel.with_open_bin header In_channel.input_all
+      with Sys_error msg -> raise (Error (Camlheader (msg, header)))
+    in
+    let zinc_runtime_id, offset =
+      if String.length data < 2 then
+        raise (Error (Camlheader ("corrupt header", header)))
+      else if data.[0] = '\000' then
+        None, 1
+      else
+        let zinc = Misc.RuntimeID.of_string (String.sub data 0 4) in
+        if Option.fold ~none:false ~some:Misc.RuntimeID.is_zinc zinc then
+          zinc, 4
+        else
+          raise (Error (Camlheader ("corrupt header", header)))
+    in
+    let write_exe_header outchan =
+      let len = String.length data in
+      Out_channel.output_substring outchan data offset (len - offset)
+    in
+    zinc_runtime_id, write_exe_header
   in
-  let runtime =
-    (* Historically, the native Windows ports are assumed to be finding
-       ocamlrun using a PATH search. *)
-    if use_runtime || Sys.win32 then
-      runtime
+  let runtime, search =
+    if String.length !Clflags.use_runtime > 0 then
+      let runtime = !Clflags.use_runtime in
+      if Filename.is_relative runtime then
+        Filename.concat (Sys.getcwd ()) runtime, Config.Disable
+      else
+        make_absolute runtime, Config.Disable
     else
-      Filename.concat runtime_info.bindir runtime
+      let runtime =
+        let runtime = "ocamlrun" ^ !Clflags.runtime_variant in
+        let some = Misc.RuntimeID.ocamlrun !Clflags.runtime_variant in
+        Option.fold ~none:runtime ~some zinc_runtime_id
+      in
+      let runtime =
+        if !Clflags.search_method = Config.Disable then
+          Filename.concat !Clflags.target_bindir runtime
+        else
+          runtime
+      in
+      runtime, !Clflags.search_method
   in
   (* Determine which method will be used for launching the executable:
      Executable: concatenate the bytecode image to the executable stub
      Shebang_runtime: #! line with the required runtime
      Shebang_bin_sh: #! for a shell script calling exec *)
   let launcher =
-    if runtime_info.launcher = Executable then
-      Executable
-    else
-      if invalid_for_shebang_line runtime then
-        match runtime_info.launcher with
-        | Shebang_bin_sh sh ->
-            let sh =
-              if sh = "sh" then
-                find_bin_sh ()
-              else
-                sh in
-            if sh = "" || invalid_for_shebang_line sh then
-              Executable
-            else
-              Shebang_bin_sh sh
-        | _ ->
+    match !Clflags.launch_method with
+    | Config.Executable ->
+        Executable
+    | Config.Shebang sh ->
+        if search <> Config.Disable || invalid_for_shebang_line runtime then
+          let sh =
+            match sh with
+            | Some sh -> sh
+            | None -> find_bin_sh ()
+          in
+          if sh = "" || invalid_for_shebang_line sh then
             Executable
-      else
-        Shebang_runtime
+          else
+            Shebang_bin_sh sh
+        else
+          Shebang_runtime
   in
+  (* Write the header *)
   match launcher with
   | Shebang_runtime ->
+      assert (search = Config.Disable);
       (* Use the runtime directly *)
       Printf.fprintf outchan "#!%s\n" runtime;
       Bytesections.init_record outchan
   | Shebang_bin_sh bin_sh ->
-      (* exec the runtime using sh *)
-      Printf.fprintf outchan "\
-        #!%s\n\
-        exec %s \"$0\" \"$@\"\n" bin_sh (Filename.quote runtime);
+      (* Use the shebang launcher *)
+      write_sh_launcher outchan bin_sh bindir search runtime;
       Bytesections.init_record outchan
   | Executable ->
       (* Use the executable stub launcher *)
-      let pos = runtime_info.executable_offset in
-      let len = String.length runtime_info.buffer - pos in
-      Out_channel.output_substring outchan runtime_info.buffer pos len;
+      write_exe_launcher outchan;
       (* The runtime name needs recording in RNTM *)
       let toc_writer = Bytesections.init_record outchan in
-      Printf.fprintf outchan "%s\000" runtime;
+      (* stdlib/header.c determines which mode is needed based on whether the
+         RNTM section contains an embedded NUL character. For Disable, the path
+         is written verbatim (no extra NUL), otherwise the directory separator
+         just before the basename is effectively turned into a NUL (for Enable,
+         there is no dirname, so the string "begins" with a NUL character). *)
+      if search = Disable then
+        output_string outchan runtime
+      else begin
+        if search = Fallback then
+          (* Ensure bindir does _not_ end up with a separator *)
+          output_string outchan
+            (Filename.(dirname (concat bindir current_dir_name)));
+        output_char outchan '\000';
+        output_string outchan runtime
+      end;
       Bytesections.record toc_writer RNTM;
       toc_writer
 
@@ -483,19 +552,36 @@ let link_bytecode ?final_name tolink exec_name standalone =
        let start_code = pos_out outchan in
        Symtable.init();
        clear_crc_interfaces ();
-       let sharedobjs = List.map Dll.extract_dll_name !Clflags.dllibs in
+       let (tocheck, sharedobjs) =
+         let process_dllib ((suffixed, name) as dllib) (tocheck, sharedobjs) =
+           let resolved_name = Dll.extract_dll_name dllib in
+           let partial_name =
+             if suffixed then
+               if String.starts_with ~prefix:"-l" name then
+                 (suffixed, "dll" ^ String.sub name 2 (String.length name - 2))
+               else
+                 dllib
+             else
+               (false, resolved_name)
+           in
+           (resolved_name::tocheck, partial_name::sharedobjs)
+         in
+         List.fold_right process_dllib !Clflags.dllibs ([], [])
+       in
        let check_dlls = standalone && Config.target = Config.host in
        if check_dlls then begin
          (* Initialize the DLL machinery *)
          Dll.init_compile !Clflags.no_std_include;
          Dll.add_path (Load_path.get_path_list ());
-         try Dll.open_dlls Dll.For_checking sharedobjs
+         try Dll.open_dlls Dll.For_checking tocheck
          with Failure reason -> raise(Error(Cannot_open_dll reason))
        end;
        let output_fun buf =
          Out_channel.output_bigarray outchan buf 0 (Bigarray.Array1.dim buf)
        and currpos_fun () = pos_out outchan - start_code in
-       List.iter (link_file output_fun currpos_fun) tolink;
+       let needs_stdlib =
+         link_files output_fun currpos_fun tolink
+       in
        if check_dlls then Dll.close_all_dlls();
        (* The final STOP instruction *)
        output_byte outchan Opcodes.opSTOP;
@@ -504,11 +590,20 @@ let link_bytecode ?final_name tolink exec_name standalone =
        (* DLL stuff *)
        if standalone then begin
          (* The extra search path for DLLs *)
-         output_string outchan (concat_null_terminated !Clflags.dllpaths);
-         Bytesections.record toc_writer DLPT;
+         if !Clflags.dllpaths <> [] then begin
+           output_string outchan (concat_null_terminated !Clflags.dllpaths);
+           Bytesections.record toc_writer DLPT
+         end;
          (* The names of the DLLs *)
-         output_string outchan (concat_null_terminated sharedobjs);
-         Bytesections.record toc_writer DLLS
+         if sharedobjs <> [] then begin
+           let output_sharedobj (suffixed, name) =
+             output_char outchan (if suffixed then '-' else ':');
+             output_string outchan name;
+             output_byte outchan 0
+           in
+           List.iter output_sharedobj sharedobjs;
+           Bytesections.record toc_writer DLLS
+         end
        end;
        (* The names of all primitives *)
        Symtable.output_primitive_names outchan;
@@ -518,6 +613,18 @@ let link_bytecode ?final_name tolink exec_name standalone =
          ~filename:final_name ~kind:"bytecode executable"
          outchan (Symtable.initial_global_table());
        Bytesections.record toc_writer DATA;
+       (* -custom executables don't need OSLD sections - the correct value is
+          already included in the runtime. *)
+       if standalone && needs_stdlib then begin
+         (* OCaml Standard Library Default location *)
+         let standard_library_default =
+           Option.value
+             ~default:Config.standard_library_default
+             !Clflags.standard_library_default
+         in
+         output_string outchan standard_library_default;
+         Bytesections.record toc_writer OSLD
+       end;
        (* The map of global identifiers *)
        Symtable.output_global_map outchan;
        Bytesections.record toc_writer SYMB;
@@ -589,6 +696,59 @@ let output_cds_file outfile =
        Bytesections.write_toc_and_trailer toc_writer;
     )
 
+let rec to_utf_8_seq b i () =
+  if i >= Bytes.length b then
+    Seq.Nil
+  else
+    let next = Bytes.get_utf_8_uchar b i in
+    let u = Uchar.utf_decode_uchar next in
+    Seq.Cons(u, to_utf_8_seq b (i + Uchar.utf_decode_length next))
+
+let to_utf_8_seq s = to_utf_8_seq (Bytes.unsafe_of_string s) 0
+
+(* [c_string_literal_of_string s] returns the C literal string representation of
+   [s], suitable for embedding in a C source file with type [char_os *]. The
+   result includes the quote markers. *)
+let c_string_literal_of_string s =
+  let b = Buffer.create (String.length s * 2) in
+  let utf16le = Bytes.create 4 in
+  let escape u =
+    match Uchar.to_int u with
+      (* Characters with C escape sequences *)
+    | 000 (* '\0' *) -> Buffer.add_string b "\\000"
+    | 009 (* '\t' *) -> Buffer.add_string b "\\t"
+    | 010 (* '\n' *) -> Buffer.add_string b "\\n"
+    | 013 (* '\r' *) -> Buffer.add_string b "\\r"
+    | 034 (* '\"' *) -> Buffer.add_string b "\\\""
+    | 092 (* '\\' *) -> Buffer.add_string b "\\\\"
+      (* Most C compilers will have no problem processing UTF-8 in the strings
+         with the characters above converted to their C representations. On
+         Windows, where the string is [wchar_t *], all characters for which
+         iswprint returns 0 are escaped using the extended [\x] notation. *)
+    | c when Sys.win32 && (c < 32 (* ' ' *) || c >= 127) ->
+        (* Convert u to UTF-16LE, allowing for surrogate pairs *)
+        let len = Bytes.set_utf_16le_uchar utf16le 0 u in
+        for i = 1 to len / 2 do
+          Printf.bprintf b "\\x%04x" (Bytes.get_uint16_le utf16le ((i - 1) * 2))
+        done
+    | _ ->
+        Buffer.add_utf_8_uchar b u
+  in
+  if Sys.win32 then
+    Buffer.add_char b 'L';
+  Buffer.add_char b '"';
+  Seq.iter escape (to_utf_8_seq s);
+  Buffer.add_char b '"';
+  Buffer.contents b
+
+let emit_runtime_standard_library_default outchan =
+  let stdlib =
+    let default = Config.standard_library_default in
+    Option.value ~default !Clflags.standard_library_default in
+  let literal = c_string_literal_of_string stdlib in
+  Printf.fprintf outchan
+    "const char_os * caml_runtime_standard_library_default = %s;\n" literal
+
 (* Output a bytecode executable as a C file *)
 
 let link_bytecode_as_c tolink outfile with_main =
@@ -603,6 +763,8 @@ let link_bytecode_as_c tolink outfile with_main =
 extern "C" {
 #endif
 
+#include <stdbool.h>
+
 #define CAML_INTERNALS
 #define CAMLDLLIMPORT
 #define CAML_INTERNALS_NO_PRIM_DECLARATIONS
@@ -612,6 +774,11 @@ extern "C" {
 #include <caml/sys.h>
 #include <caml/misc.h>
 
+extern const char_os *caml_runtime_standard_library_default;
+
+enum caml_byte_program_mode caml_byte_program_mode = COMPLETE_EXE;
+const bool caml_byte_program_mode_custom = false;
+
 static int caml_code[] = {
 |};
        Symtable.init();
@@ -621,7 +788,7 @@ static int caml_code[] = {
          output_code_string outchan code;
          currpos := !currpos + (Bigarray.Array1.dim code)
        and currpos_fun () = !currpos in
-       List.iter (link_file output_fun currpos_fun) tolink;
+       ignore (link_files output_fun currpos_fun tolink);
        (* The final STOP instruction *)
        Printf.fprintf outchan "\n0x%x};\n" Opcodes.opSTOP;
        (* The table of global data *)
@@ -649,6 +816,7 @@ static char caml_sections[] = {
 };
 
 |};
+       emit_runtime_standard_library_default outchan;
        (* The table of primitives *)
        Symtable.output_primitive_table outchan;
        (* The entry point *)
@@ -656,7 +824,6 @@ static char caml_sections[] = {
          output_string outchan {|
 int main_os(int argc, char_os **argv)
 {
-  caml_byte_program_mode = COMPLETE_EXE;
   caml_startup_code(caml_code, sizeof(caml_code),
                     caml_data, sizeof(caml_data),
                     caml_sections, sizeof(caml_sections),
@@ -714,13 +881,20 @@ value caml_startup_pooled_exn(char_os ** argv)
   if not with_main && !Clflags.debug then
     output_cds_file ((Filename.chop_extension outfile) ^ ".cds")
 
+let runtime_library_name runtime_variant =
+  if runtime_variant = "_shared" && Config.suffixing then
+    Misc.RuntimeID.shared_runtime Sys.Bytecode
+  else
+    "-lcamlrun" ^ runtime_variant
+
 (* Build a custom runtime *)
 
 let build_custom_runtime prim_name exec_name =
   let runtime_lib =
     if not !Clflags.with_runtime
     then ""
-    else "-lcamlrun" ^ !Clflags.runtime_variant in
+    else runtime_library_name !Clflags.runtime_variant
+  in
   let stable_name =
     if not !Clflags.keep_camlprimc_file then
       Some "camlprim.c"
@@ -798,11 +972,22 @@ let link objfiles output_name =
 extern "C" {
 #endif
 
+#define CAML_INTERNALS
 #define CAML_INTERNALS_NO_PRIM_DECLARATIONS
+
+#include <stdbool.h>
+
 #include <caml/mlvalues.h>
+#include <caml/startup.h>
+
+extern const char_os *caml_runtime_standard_library_default;
+
+enum caml_byte_program_mode caml_byte_program_mode = STANDARD;
+const bool caml_byte_program_mode_custom = true;
 
 |};
          Symtable.output_primitive_table poc;
+         emit_runtime_standard_library_default poc;
          output_string poc {|
 #ifdef __cplusplus
 }
@@ -857,7 +1042,8 @@ extern "C" {
                  let runtime_lib =
                    if not !Clflags.with_runtime
                    then ""
-                   else "-lcamlrun" ^ !Clflags.runtime_variant in
+                   else runtime_library_name !Clflags.runtime_variant
+                 in
                  Ccomp.call_linker mode output_name
                    ([obj_file] @ List.rev !Clflags.ccobjs @ [runtime_lib])
                    c_libs = 0
diff --git a/bytecomp/bytelink.mli b/bytecomp/bytelink.mli
index 61dffee8779c..9a8d7a4da47a 100644
--- a/bytecomp/bytelink.mli
+++ b/bytecomp/bytelink.mli
@@ -30,6 +30,8 @@ val linkdeps_unit :
 
 val extract_crc_interfaces: unit -> crcs
 
+val to_utf_8_seq : string -> Uchar.t Seq.t
+
 type error =
   | File_not_found of filepath
   | Not_an_object_file of filepath
diff --git a/bytecomp/bytesections.ml b/bytecomp/bytesections.ml
index 30a1c0fbc9ec..dd848a7de719 100644
--- a/bytecomp/bytesections.ml
+++ b/bytecomp/bytesections.ml
@@ -26,6 +26,7 @@ module Name = struct
     | DBUG (** debug info *)
     | DLLS (** dll names *)
     | DLPT (** dll paths *)
+    | OSLD (** OCaml Standard Library Default location *)
     | PRIM (** primitives names *)
     | RNTM (** The path to the bytecode interpreter (use_runtime mode) *)
     | SYMB (** global identifiers *)
@@ -37,6 +38,7 @@ module Name = struct
     | "DLPT" -> DLPT
     | "DLLS" -> DLLS
     | "DATA" -> DATA
+    | "OSLD" -> OSLD
     | "PRIM" -> PRIM
     | "SYMB" -> SYMB
     | "DBUG" -> DBUG
@@ -52,6 +54,7 @@ module Name = struct
     | DLPT -> "DLPT"
     | DLLS -> "DLLS"
     | DATA -> "DATA"
+    | OSLD -> "OSLD"
     | PRIM -> "PRIM"
     | SYMB -> "SYMB"
     | DBUG -> "DBUG"
diff --git a/bytecomp/bytesections.mli b/bytecomp/bytesections.mli
index 3d287932ac29..e6f9e6af1d56 100644
--- a/bytecomp/bytesections.mli
+++ b/bytecomp/bytesections.mli
@@ -27,6 +27,7 @@ module Name : sig
     | DBUG (** debug info *)
     | DLLS (** dll names *)
     | DLPT (** dll paths *)
+    | OSLD (** OCaml Standard Library Default location *)
     | PRIM (** primitives names *)
     | RNTM (** The path to the bytecode interpreter (use_runtime mode) *)
     | SYMB (** global identifiers *)
diff --git a/bytecomp/dll.ml b/bytecomp/dll.ml
index f86efc6e93be..24028f21bd8a 100644
--- a/bytecomp/dll.ml
+++ b/bytecomp/dll.ml
@@ -51,13 +51,41 @@ let remove_path dirs =
 
 (* Extract the name of a DLLs from its external name (xxx.so or -lxxx) *)
 
-let extract_dll_name file =
-  if Filename.check_suffix file Config.ext_dll then
+let extract_dll_name (suffixed, file) =
+  if not suffixed && Filename.check_suffix file Config.ext_dll then
     Filename.chop_suffix file Config.ext_dll
-  else if String.length file >= 2 && String.sub file 0 2 = "-l" then
-    "dll" ^ String.sub file 2 (String.length file - 2)
   else
-    file (* will cause error later *)
+    let file =
+      if String.starts_with ~prefix:"-l" file then
+      "dll" ^ String.sub file 2 (String.length file - 2)
+    else
+      file
+    in
+      if suffixed then
+        Misc.RuntimeID.stubslib file
+      else
+        file
+
+(* This dance avoids the need to bump the magic number for .cma format, which is
+   a bit awkward to do with old releases, because we don't reserve indexes for
+   maintenance releases. In OCaml 5.5+, Cmo_format.lib_dllibs is a
+   (suffixed:bool * string) list, but for these backports we instead keep the
+   old string list for Cmo_format.lib_dllibs and append a bool list after the
+   toc. This value is guarded by the cma magic number written in reverse. *)
+let rebmun_cigam_amc =
+  let magic_length = String.length Config.cma_magic_number in
+  let init i = Config.cma_magic_number.[magic_length - i - 1] in
+  String.init magic_length init
+
+let read_suffixed_dllibs_from_channel ic l =
+  let open Cmo_format in
+  let magic_length = String.length Config.cma_magic_number in
+  match In_channel.really_input_string ic magic_length with
+  | Some magic when magic = rebmun_cigam_amc ->
+      let combine suffixed l acc = (suffixed, l)::acc in
+      List.fold_right2 combine (input_value ic : bool list) l.lib_dllibs []
+  | _ ->
+      List.map (fun l -> (false, l)) l.lib_dllibs
 
 (* Open a list of DLLs, adding them to opened_dlls.
    Raise [Failure msg] in case of error. *)
@@ -138,22 +166,7 @@ let synchronize_primitive num symb =
     assert (actual_num = num)
   end
 
-(* Read the [ld.conf] file and return the corresponding list of directories *)
-
-let ld_conf_contents () =
-  let path = ref [] in
-  begin try
-    let ic = open_in (Filename.concat Config.standard_library "ld.conf") in
-    begin try
-      while true do
-        path := input_line ic :: !path
-      done
-    with End_of_file -> ()
-    end;
-    close_in ic
-  with Sys_error _ -> ()
-  end;
-  List.rev !path
+external ld_conf_contents : string -> string list = "caml_dynlink_parse_ld_conf"
 
 (* Split the CAML_LD_LIBRARY_PATH environment variable and return
    the corresponding list of directories.  *)
@@ -169,7 +182,7 @@ let ld_library_path_contents () =
 let init_compile nostdlib =
   search_path :=
     ld_library_path_contents() @
-    (if nostdlib then [] else ld_conf_contents())
+    (if nostdlib then [] else ld_conf_contents Config.standard_library_default)
 
 (* Initialization for linking in core (dynlink or toplevel) *)
 
diff --git a/bytecomp/dll.mli b/bytecomp/dll.mli
index 216fea828014..e92be9f08dbb 100644
--- a/bytecomp/dll.mli
+++ b/bytecomp/dll.mli
@@ -15,8 +15,14 @@
 
 (* Handling of dynamically-linked libraries *)
 
-(* Extract the name of a DLLs from its external name (xxx.so or -lxxx) *)
-val extract_dll_name: string -> string
+(* Extract the name of a DLL from its mangled or external name. If the flag is
+   [true] then the name is just the undecorated basename of the DLL (no -l and
+   no .so). If the flag is [false] then the external name may include the DLL
+   extension or linking symbol (xxx.so or -lxxx) *)
+val extract_dll_name: (bool * string) -> string
+
+val read_suffixed_dllibs_from_channel:
+  in_channel -> Cmo_format.library -> (bool * string) list
 
 type dll_mode =
   | For_checking     (* will just check existence of symbols;
diff --git a/configure b/configure
index 2b8e81bc3d2b..a763699fcac3 100755
--- a/configure
+++ b/configure
@@ -56,7 +56,7 @@ if test -e '.git' ; then :
   fi
 fi
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.71 for OCaml 5.3.1+dev0-2025-01-06.
+# Generated by GNU Autoconf 2.71 for OCaml 5.3.1+relocatable.
 #
 # Report bugs to <caml-list@inria.fr>.
 #
@@ -677,8 +677,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='OCaml'
 PACKAGE_TARNAME='ocaml'
-PACKAGE_VERSION='5.3.1+dev0-2025-01-06'
-PACKAGE_STRING='OCaml 5.3.1+dev0-2025-01-06'
+PACKAGE_VERSION='5.3.1+relocatable'
+PACKAGE_STRING='OCaml 5.3.1+relocatable'
 PACKAGE_BUGREPORT='caml-list@inria.fr'
 PACKAGE_URL='http://www.ocaml.org'
 
@@ -785,10 +785,23 @@ build_os
 build_vendor
 build_cpu
 build
+runtime_search_target
+runtime_search
+suffixing
+native_runtime_id
+bytecode_runtime_id
+zinc_runtime_id
+build_map_flags
+srcdir_abs_real
+srcdir_abs
+target_libdir_is_relative
 ar_supports_response_files
 QS
+TARGET_LIBDIR
 ocaml_libdir
+TARGET_BINDIR
 ocaml_bindir
+ocaml_prefix
 compute_deps
 build_libraries_manpages
 PACKLD
@@ -832,6 +845,7 @@ build_ocamldoc
 build_ocamltex
 build_ocamldebug
 with_debugger
+as_is_cc
 as_has_debug_prefix_map
 cc_has_debug_prefix_map
 unix_directory
@@ -858,6 +872,8 @@ natdynlink
 supports_shared_libraries
 mklib
 AR
+launch_method_target
+launch_method
 shebangscripts
 winpthreads_source_include_dir
 winpthreads_source_dir
@@ -928,6 +944,7 @@ CMO_MAGIC_NUMBER
 CMI_MAGIC_NUMBER
 EXEC_MAGIC_NUMBER
 MAGIC_LENGTH
+OCAML_RELEASE_NUMBER
 OCAML_VERSION_SHORT
 OCAML_VERSION_EXTRA
 OCAML_VERSION_PATCHLEVEL
@@ -1012,6 +1029,7 @@ enable_flambda_invariants
 enable_cmm_invariants
 with_target_bindir
 with_target_sh
+with_additional_stublibsdir
 enable_reserved_header_bits
 enable_stdlib_manpages
 enable_warn_error
@@ -1019,6 +1037,10 @@ enable_force_safe_string
 enable_flat_float_array
 enable_function_sections
 enable_mmap_map_stack
+with_relative_libdir
+enable_suffixing
+enable_runtime_search
+enable_runtime_search_target
 with_afl
 with_flexdll
 with_winpthreads_msvc
@@ -1602,7 +1624,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures OCaml 5.3.1+dev0-2025-01-06 to adapt to many kinds of systems.
+\`configure' configures OCaml 5.3.1+relocatable to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1669,7 +1691,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of OCaml 5.3.1+dev0-2025-01-06:";;
+     short | recursive ) echo "Configuration of OCaml 5.3.1+relocatable:";;
    esac
   cat <<\_ACEOF
 
@@ -1721,6 +1743,13 @@ Optional Features:
   --disable-function-sections
                           do not emit each function in a separate section
   --enable-mmap-map-stack use mmap to allocate stacks instead of malloc
+  --disable-suffixing     disable suffixing of runtime executables and shared
+                          libraries
+  --enable-runtime-search allow the distribution's bytecode executables to
+                          search for ocamlrun
+  --enable-runtime-search-target
+                          allow bytecode executables produced by ocamlc to
+                          search for ocamlrun
   --enable-shared[=PKGS]  build shared libraries [default=yes]
   --enable-static[=PKGS]  build static libraries [default=yes]
   --enable-fast-install[=PKGS]
@@ -1734,6 +1763,12 @@ Optional Packages:
   --with-target-bindir    location of the runtime binaries on the target
                           system
   --with-target-sh        location of Posix sh on the target system
+  --with-additional-stublibsdir
+                          additional directory for searching for bytecode stub
+                          libraries
+  --with-relative-libdir  location of the Standard Library, specified relative
+                          to --bindir (if no argument is given to
+                          --with-relative-libdir, defaults to ../lib/ocaml)
   --with-afl              use the AFL fuzzer
   --with-flexdll          bootstrap FlexDLL from the given sources
   --with-winpthreads-msvc build winpthreads (only for the MSVC port) from the
@@ -1851,7 +1886,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-OCaml configure 5.3.1+dev0-2025-01-06
+OCaml configure 5.3.1+relocatable
 generated by GNU Autoconf 2.71
 
 Copyright (C) 2021 Free Software Foundation, Inc.
@@ -2508,7 +2543,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by OCaml $as_me 5.3.1+dev0-2025-01-06, which was
+It was created by OCaml $as_me 5.3.1+relocatable, which was
 generated by GNU Autoconf 2.71.  Invocation command line was
 
   $ $0$ac_configure_args_raw
@@ -3264,8 +3299,28 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: Configuring OCaml version 5.3.1+dev0-2025-01-06" >&5
-printf "%s\n" "$as_me: Configuring OCaml version 5.3.1+dev0-2025-01-06" >&6;}
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: Configuring OCaml version 5.3.1+relocatable" >&5
+printf "%s\n" "$as_me: Configuring OCaml version 5.3.1+relocatable" >&6;}
+
+# It's important for the setting up of defaults and the checking of the
+# --with-relative-libdir option to know whether the user specified --libdir.
+# Unfortunately, autoconf doesn't provide an easy way to determine this, so we
+# simply repeat autoconf's argument parsing for the libdir and mandir options.
+# This is done early in the script to ensure that only autoconf and site-config
+# scripts have run.
+libdir_given=no
+mandir_given=no
+for ac_arg
+do
+  case $ac_arg in
+    -mandir=* | --mandir=* | --mandi=* | --mand=* | --man=* | --ma=* | --m=* | \
+    -mandir | --mandir | --mandi | --mand | --man | --ma | --m)
+      mandir_given=yes;;
+    -libdir=* | --libdir=* | --libdi=* | --libd=* | \
+    -libdir   | --libdir   | --libdi   | --libd)
+      libdir_given=yes;;
+  esac
+done
 
 # Configuration variables
 
@@ -3325,6 +3380,12 @@ ocamltest_libunix=None
 ocamltest_unix_impl="dummy"
 unix_library=""
 unix_directory=""
+target_libdir_is_relative=false
+srcdir_abs=''
+srcdir_abs_real=''
+build_map_flags=''
+runtime_search=''
+runtime_search_target=''
 
 # Information about the package
 
@@ -3339,11 +3400,11 @@ unix_directory=""
 
 
 
-VERSION=5.3.1+dev0-2025-01-06
+VERSION=5.3.1+relocatable
 
 OCAML_DEVELOPMENT_VERSION=true
 
-OCAML_RELEASE_EXTRA='Some (Plus, "dev0-2025-01-06")'
+OCAML_RELEASE_EXTRA='Some (Plus, "relocatable")'
 
 OCAML_VERSION_MAJOR=5
 
@@ -3351,10 +3412,12 @@ OCAML_VERSION_MINOR=3
 
 OCAML_VERSION_PATCHLEVEL=1
 
-OCAML_VERSION_EXTRA=dev0-2025-01-06
+OCAML_VERSION_EXTRA=relocatable
 
 OCAML_VERSION_SHORT=5.3
 
+OCAML_RELEASE_NUMBER=19
+
 printf "%s\n" "#define MAGIC_NUMBER_PREFIX \"Caml1999\"" >>confdefs.h
 
 printf "%s\n" "#define MAGIC_NUMBER_VERSION \"035\"" >>confdefs.h
@@ -3470,6 +3533,9 @@ LINEAR_MAGIC_NUMBER=Caml1999L035
 
 
 
+
+
+
 
 
 
@@ -3508,6 +3574,19 @@ LINEAR_MAGIC_NUMBER=Caml1999L035
 
 
 
+
+
+
+
+
+
+
+
+
+
+
+
+
 
 
 
@@ -3530,10 +3609,6 @@ ac_config_files="$ac_config_files Makefile.config"
 
 ac_config_files="$ac_config_files stdlib/sys.ml"
 
-ac_config_files="$ac_config_files manual/src/version.tex"
-
-ac_config_files="$ac_config_files manual/src/html_processing/src/common.ml"
-
 ac_config_files="$ac_config_files ocamltest/ocamltest_config.ml"
 
 ac_config_files="$ac_config_files otherlibs/dynlink/dynlink_config.ml"
@@ -3548,6 +3623,8 @@ ac_config_headers="$ac_config_headers runtime/caml/m.h"
 
 ac_config_headers="$ac_config_headers runtime/caml/s.h"
 
+ac_config_headers="$ac_config_headers runtime/sys_int.h"
+
 ac_config_headers="$ac_config_headers runtime/caml/version.h"
 
 ac_config_files="$ac_config_files compilerlibs/META"
@@ -3560,6 +3637,13 @@ ac_config_files="$ac_config_files stdlib/META"
 
 ac_config_files="$ac_config_files testsuite/tools/toolchain.ml"
 
+if test -d manual
+then :
+  ac_config_files="$ac_config_files manual/src/version.tex"
+
+  ac_config_files="$ac_config_files manual/src/html_processing/src/common.ml"
+
+fi
 
 # Definitions related to the version of OCaml
 printf "%s\n" "#define OCAML_VERSION_MAJOR 5" >>confdefs.h
@@ -3568,13 +3652,15 @@ printf "%s\n" "#define OCAML_VERSION_MINOR 3" >>confdefs.h
 
 printf "%s\n" "#define OCAML_VERSION_PATCHLEVEL 1" >>confdefs.h
 
-printf "%s\n" "#define OCAML_VERSION_ADDITIONAL \"dev0-2025-01-06\"" >>confdefs.h
+printf "%s\n" "#define OCAML_VERSION_ADDITIONAL \"relocatable\"" >>confdefs.h
 
-  printf "%s\n" "#define OCAML_VERSION_EXTRA \"dev0-2025-01-06\"" >>confdefs.h
+  printf "%s\n" "#define OCAML_VERSION_EXTRA \"relocatable\"" >>confdefs.h
 
 printf "%s\n" "#define OCAML_VERSION 50301" >>confdefs.h
 
-printf "%s\n" "#define OCAML_VERSION_STRING \"5.3.1+dev0-2025-01-06\"" >>confdefs.h
+printf "%s\n" "#define OCAML_VERSION_STRING \"5.3.1+relocatable\"" >>confdefs.h
+
+printf "%s\n" "#define OCAML_RELEASE_NUMBER 19" >>confdefs.h
 
 
 # Works out how many "o"s are needed in quoted strings
@@ -3699,12 +3785,47 @@ test -n "$target_alias" &&
     NONENONEs,x,x, &&
   program_prefix=${target_alias}-
 
+# $cygwin_build_env=true if the build is taking place in any kind of Cygwin-like
+# environment (which may include cross-compiling _from_ Cygwin)
+# All patterns end with * (cf. build-aux/config.sub)
+#
+# In Cygwin itself, the mingw-w64 compilers are cross-compilers
+# (host=x86_64-pc-cygwin; target=*-w64-mingw32) and $build when running from
+# within Cygwin is always *-pc-cygwin.
+#
+# In MSYS2, the mingw-w64 compilers are normal host compilers, which MSYS2 makes
+# available through different Environments (similar to the Microsoft Visual
+# Studio Tools Command Prompts; see https://www.msys2.org/docs/environments/).
+# It is possible to use MSYS2's "Cygwin" gcc (the equivalent of compiling native
+# Cygwin), in which case $build is *-*-cygwin (some older MSYS2 installations
+# may report the legacy *-*-msys*)
+# The mingw-w64 Environments manually set $build to *-w64-mingw32, but the
+# _native_ value inferred by config.guess (which uses uname -s) will be
+# *-pc-mingw32 (for the 32-bit _target_ environments, even though MSYS2 is a
+# 64-bit build environment) and *-pc-mingw64 (for the 64-bit _target_
+# environments).
+#
+# This leads to the four patterns below, all of which imply that the build is
+# taking place on a system where Cygwin's utilities (cygpath, etc.) can be
+# expected to be found and its semantics (CYGWIN=winsymlinks:native, etc.) be
+# expected to apply.
+#
+# Note that although build=x86_64-pc-mingw64 will be accepted here, it is highly
+# likely that that's a misconfigured environment, and the script will
+# subsequently fail if host has not been altered to x86_64-w64-mingw32.
+case $build in #(
+  *-*-cygwin*|*-*-msys*|*-*-mingw32*|*-*-mingw64*) :
+    cygwin_build_env=true ;; #(
+  *) :
+    cygwin_build_env=false ;;
+esac
+
 # Ensure that AC_CONFIG_LINKS will either create symlinks which are compatible
 # with native Windows (i.e. NTFS symlinks, not WSL or Cygwin-emulated ones) or
 # use its fallback mechanisms. Native Windows versions of ocamlc/ocamlopt cannot
 # interpret either WSL or Cygwin-emulated symlinks.
-case $host in #(
-  *-pc-windows|*-w64-mingw32*) :
+case $cygwin_build_env,$host in #(
+  true,*-pc-windows|true,*-w64-mingw32*) :
     ac_config_commands="$ac_config_commands native-symlinks"
  ;; #(
   *) :
@@ -3803,6 +3924,15 @@ printf "%s\n" "$as_me: WARNING: Mono is not yet supported - C sharp tests disabl
 esac
 fi
 
+# Environment-specific set-up
+
+case $target in #(
+  *-w64-mingw32*|*-pc-windows) :
+    default_separator='\' ;; #(
+  *) :
+    default_separator='/' ;;
+esac
+
 # Environment variables that are taken into account
 
 
@@ -4060,9 +4190,9 @@ fi
 # Check whether --with-target-bindir was given.
 if test ${with_target_bindir+y}
 then :
-  withval=$with_target_bindir; target_bindir=$withval
+  withval=$with_target_bindir; TARGET_BINDIR=$withval
 else $as_nop
-  target_bindir=''
+  TARGET_BINDIR=''
 fi
 
 
@@ -4072,12 +4202,29 @@ if test ${with_target_sh+y}
 then :
   withval=$with_target_sh; if test x"$withval" = 'xno'
 then :
-  target_launch_method='exe'
+  launch_method_target='exe'
 else $as_nop
-  target_launch_method="$withval"
+  launch_method_target="$withval"
 fi
 else $as_nop
-  target_launch_method=''
+  launch_method_target=''
+fi
+
+
+
+# Check whether --with-additional-stublibsdir was given.
+if test ${with_additional_stublibsdir+y}
+then :
+  withval=$with_additional_stublibsdir; case $withval in #(
+  no) :
+    ocaml_additional_stublibs_dir='' ;; #(
+  yes) :
+    ocaml_additional_stublibs_dir="..${default_separator}stublibs" ;; #(
+  *) :
+    ocaml_additional_stublibs_dir="$withval" ;;
+esac
+else $as_nop
+  ocaml_additional_stublibs_dir=''
 fi
 
 
@@ -4151,6 +4298,82 @@ fi
 
 
 
+# Check whether --with-relative-libdir was given.
+if test ${with_relative_libdir+y}
+then :
+  withval=$with_relative_libdir; case $withval in #(
+  no) :
+    bindir_to_libdir='' ;; #(
+  yes) :
+    bindir_to_libdir="..${default_separator}lib${default_separator}ocaml" ;; #(
+  *) :
+    bindir_to_libdir="$withval" ;;
+esac
+else $as_nop
+  bindir_to_libdir=''
+fi
+
+
+# Check whether --enable-suffixing was given.
+if test ${enable_suffixing+y}
+then :
+  enableval=$enable_suffixing; if test "x$enableval" = 'xno'
+then :
+  suffixing=false
+else $as_nop
+  suffixing=true
+fi
+else $as_nop
+  suffixing=auto
+fi
+
+
+# Check whether --enable-runtime-search was given.
+if test ${enable_runtime_search+y}
+then :
+  enableval=$enable_runtime_search; case $enableval in #(
+  no) :
+     ;; #(
+  yes) :
+    runtime_search='enable' ;; #(
+  fallback) :
+    runtime_search='fallback' ;; #(
+  *) :
+    as_fn_error $? "valid values are yes, no or fallback for --enable-runtime-search" "$LINENO" 5 ;;
+esac
+fi
+
+
+# Check whether --enable-runtime-search-target was given.
+if test ${enable_runtime_search_target+y}
+then :
+  enableval=$enable_runtime_search_target; case $enableval in #(
+  no) :
+     ;; #(
+  yes) :
+    runtime_search_target='enable' ;; #(
+  fallback) :
+    runtime_search_target='fallback' ;; #(
+  *) :
+    as_fn_error $? "valid values are yes, no or fallback for --enable-runtime-search-target" "$LINENO" 5 ;;
+esac
+fi
+
+
+case $suffixing,$runtime_search,$runtime_search_target in #(
+  true,*,*|false,,) :
+     ;; #(
+  auto,,) :
+    suffixing=false ;; #(
+  auto,*,*) :
+    suffixing=true ;; #(
+  false,*,*) :
+    as_fn_error $? "--disable-suffixed cannot be used with --enable-runtime-search or --enable-runtime-search-target" "$LINENO" 5 ;; #(
+  *) :
+     ;;
+esac
+
+
 # Check whether --with-afl was given.
 if test ${with_afl+y}
 then :
@@ -13816,8 +14039,8 @@ esac
 # See https://lists.gnu.org/archive/html/autoconf/2019-07/msg00002.html
 # for the detailed explanation.
 
-ocamlsrcdir=$(unset CDPATH; cd -- "$srcdir" && printf %sX "$PWD") || fail
-ocamlsrcdir=${ocamlsrcdir%X}
+srcdir_abs=$(unset CDPATH; cd -- "$srcdir" && printf %sX "$PWD") || fail
+srcdir_abs=${srcdir_abs%X}
 
 # Whether ar supports @FILE arguments
 
@@ -13830,17 +14053,30 @@ esac
 
 # Libraries to build depending on the host
 
-case $host in #(
-  *-*-mingw32*|*-pc-windows) :
+case $cygwin_build_env,$host in #(
+  true,*-*-mingw32*|true,*-pc-windows) :
     unix_or_win32="win32"
-    ln='cp -pf'
+
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for a workable solution for ln -sf" >&5
+printf %s "checking for a workable solution for ln -sf... " >&6; }
+  if MSYS=winsymlinks:nativestrict CYGWIN=winsymlinks:nativestrict ln -sf configure conftestLink 2>/dev/null
+then :
+  ln='ln -sf'
+else $as_nop
+  ln='cp -pf'
+
+fi
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ln" >&5
+printf "%s\n" "$ln" >&6; }
+
     ocamltest_libunix="Some false"
-    ocamlsrcdir="$(LC_ALL=C.UTF-8 cygpath -w -- "$ocamlsrcdir")"
+    ocamlsrcdir="$(LC_ALL=C.UTF-8 cygpath -w -- "$srcdir_abs")"
     ocamlyacc_wstr_module="yacc/wstr" ;; #(
   *) :
     unix_or_win32="unix"
   ln='ln -sf'
   ocamltest_libunix="Some true"
+  ocamlsrcdir="$srcdir_abs"
   ocamlyacc_wstr_module="" ;;
 esac
 
@@ -13924,9 +14160,9 @@ then :
       # not use shebang scripts
       shebangscripts=true
       launch_method='sh'
-      if test x"$target_launch_method" = 'x'
+      if test x"$launch_method_target" = 'x'
 then :
-  target_launch_method='exe'
+  launch_method_target='exe'
 fi ;; #(
   *-*-mingw32*|*-pc-windows) :
      ;; #(
@@ -13938,21 +14174,6 @@ esac
 
 fi
 
-# stdlib/runtime.info and stdlib/target_runtime.info are generated by commands
-# in config.status, rather than by the .in mechanism, since the latter cannot
-# reliably process binary files.
-ac_config_commands="$ac_config_commands shebang"
-
-
-# Are we building a cross-compiler
-
-if test x"$host" = x"$target"
-then :
-  cross_compiler=false
-else $as_nop
-  cross_compiler=true
-fi
-
 # Checks for programs
 
 ## Check for the C compiler: done by libtool
@@ -14489,16 +14710,16 @@ rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
     if test x"$build" != x"$host"
 then :
 
-      case $build in #(
-  *-pc-msys|*-pc-cygwin*) :
-    flexlink_where="$(cmd /c "$flexlink" -where 2>/dev/null)"
-          if test -z "$flexlink_where"
+      if $cygwin_build_env
+then :
+  flexlink_where="$(cmd /c "$flexlink" -where 2>/dev/null)"
+        if test -z "$flexlink_where"
 then :
   as_fn_error $? "$flexlink is not executable from a native Win32 process" "$LINENO" 5
-fi ;; #(
-  *) :
-     ;;
-esac
+
+fi
+
+fi
 
 fi
 
@@ -14993,6 +15214,13 @@ then :
 
 fi
 
+ac_fn_c_check_header_compile "$LINENO" "libgen.h" "ac_cv_header_libgen_h" "$ac_includes_default"
+if test "x$ac_cv_header_libgen_h" = xyes
+then :
+  printf "%s\n" "#define HAS_LIBGEN_H 1" >>confdefs.h
+
+fi
+
 ac_fn_c_check_header_compile "$LINENO" "pthread_np.h" "ac_cv_header_pthread_np_h" "$ac_includes_default"
 if test "x$ac_cv_header_pthread_np_h" = xyes
 then :
@@ -16568,30 +16796,45 @@ fi
 # to avoiding forking a C compiler process for each compilation by ocamlopt.
 # Both AS and ASPP can be overridden by the user.
 
-default_as="$CC -c"
-default_aspp="$CC -c"
+as_is_cc=true
+default_as=''
 
 case $as_target,$ocaml_cc_vendor in #(
   *-*-linux*,gcc-*) :
     case $as_cpu in #(
   x86_64|arm*|aarch64*|i[3-6]86|riscv*) :
-    default_as="${toolpref}as" ;; #(
+    default_as="${toolpref}as"
+        as_is_cc=false ;; #(
   *) :
      ;;
 esac ;; #(
+  *-*-cygwin,gcc-*) :
+    default_as="${toolpref}as"
+    as_is_cc=false ;; #(
   i686-pc-windows,*) :
     default_as="ml -nologo -coff -Cp -c -Fo"
-    default_aspp="$default_as" ;; #(
+    default_aspp="$default_as"
+    as_is_cc=false ;; #(
   x86_64-pc-windows,*) :
     default_as="ml64 -nologo -Cp -c -Fo"
-    default_aspp="$default_as" ;; #(
+    default_aspp="$default_as"
+    as_is_cc=false ;; #(
   *-*-darwin*,clang-*) :
-    default_as="$default_as -Wno-trigraphs"
+    default_as="$CC -c -Wno-trigraphs"
     default_aspp="$default_as" ;; #(
   *) :
      ;;
 esac
 
+if test -z "$default_as"
+then :
+  default_as="$CC -c"
+fi
+if test -z "$default_aspp"
+then :
+  default_aspp="$CC -c"
+fi
+
 if test "$with_pic"
 then :
   fpic=true
@@ -16937,6 +17180,15 @@ then :
 fi
 
 
+## strlcpy
+ac_fn_c_check_func "$LINENO" "strlcpy" "ac_cv_func_strlcpy"
+if test "x$ac_cv_func_strlcpy" = xyes
+then :
+  printf "%s\n" "#define HAS_STRLCPY 1" >>confdefs.h
+
+fi
+
+
 ## secure_getenv and __secure_getenv
 
 saved_CPPFLAGS="$CPPFLAGS"
@@ -18409,8 +18661,6 @@ fi
 
 ## -fdebug-prefix-map support by the C compiler
 case $ocaml_cc_vendor,$host in #(
-  *,*-*-mingw32*) :
-    cc_has_debug_prefix_map=false ;; #(
   *,*-pc-windows) :
     cc_has_debug_prefix_map=false ;; #(
   xlc*,powerpc-ibm-aix*) :
@@ -18460,6 +18710,100 @@ fi
  ;;
 esac
 
+## -ffile-prefix-map support by the C compiler - used in the build, not by
+## the compiler
+if test x"$bindir_to_libdir" != 'x'
+then :
+  srcdir_abs_real="$(realpath "$srcdir_abs" 2>/dev/null)"
+  if test x"$srcdir_abs_real" = "x$srcdir_abs"
+then :
+  srcdir_abs_real=''
+fi
+  as_CACHEVAR=`printf "%s\n" "ax_cv_check_cflags_$warn_error_flag_-Wa,--debug-prefix-map=old=new" | $as_tr_sh`
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether the C compiler accepts -Wa,--debug-prefix-map=old=new" >&5
+printf %s "checking whether the C compiler accepts -Wa,--debug-prefix-map=old=new... " >&6; }
+if eval test \${$as_CACHEVAR+y}
+then :
+  printf %s "(cached) " >&6
+else $as_nop
+
+  ax_check_save_flags=$CFLAGS
+  CFLAGS="$CFLAGS $warn_error_flag -Wa,--debug-prefix-map=old=new"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"
+then :
+  eval "$as_CACHEVAR=yes"
+else $as_nop
+  eval "$as_CACHEVAR=no"
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+  CFLAGS=$ax_check_save_flags
+fi
+eval ac_res=\$$as_CACHEVAR
+	       { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
+printf "%s\n" "$ac_res" >&6; }
+if eval test \"x\$"$as_CACHEVAR"\" = x"yes"
+then :
+  build_map_flags='-Wa,--debug-prefix-map='
+else $as_nop
+  :
+fi
+
+  as_CACHEVAR=`printf "%s\n" "ax_cv_check_cflags_$warn_error_flag_-ffile-prefix-map=old=new" | $as_tr_sh`
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether the C compiler accepts -ffile-prefix-map=old=new" >&5
+printf %s "checking whether the C compiler accepts -ffile-prefix-map=old=new... " >&6; }
+if eval test \${$as_CACHEVAR+y}
+then :
+  printf %s "(cached) " >&6
+else $as_nop
+
+  ax_check_save_flags=$CFLAGS
+  CFLAGS="$CFLAGS $warn_error_flag -ffile-prefix-map=old=new"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"
+then :
+  eval "$as_CACHEVAR=yes"
+else $as_nop
+  eval "$as_CACHEVAR=no"
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+  CFLAGS=$ax_check_save_flags
+fi
+eval ac_res=\$$as_CACHEVAR
+	       { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
+printf "%s\n" "$ac_res" >&6; }
+if eval test \"x\$"$as_CACHEVAR"\" = x"yes"
+then :
+  build_map_flags="$build_map_flags -ffile-prefix-map="
+else $as_nop
+  if $cc_has_debug_prefix_map
+then :
+  build_map_flags="$build_map_flags -fdebug-prefix-map="
+fi
+fi
+
+fi
+
 ## Does stat support nanosecond precision
 
 stat_has_ns_precision=false
@@ -20979,12 +21323,12 @@ esac
 
 
 
-if test x"$libdir" = x'${exec_prefix}/lib'
+if test x"$libdir_given" = 'xno'
 then :
   libdir="$libdir"/ocaml
 fi
 
-if test x"$mandir" = x'${datarootdir}/man'
+if test x"$mandir_given" = 'xno'
 then :
   mandir='${prefix}/man'
 fi
@@ -21004,16 +21348,86 @@ then :
   *) :
      ;;
 esac
-else $as_nop
-  if test x"$unix_or_win32" = "xwin32" \
-          && test "$host_vendor-$host_os" != "$build_vendor-$build_os"
-then :
-  case $build in #(
-  *-pc-cygwin) :
-    prefix="$(LC_ALL=C.UTF-8 cygpath -m "$prefix")" ;; #(
+fi
+
+# Normalise $prefix, if necessary, on Windows. There are 7 variables to be
+# considered:
+# - $prefix and $exec_prefix. These are autoconf variables containing the values
+#   specified for --prefix and --exec-prefix respectively, or NONE if these
+#   flags were not given on the command line. These two variables are written to
+#   Makefile.config and are in _build_ format. On native Windows, the values
+#   must be suitable to pass to _both_ native Windows processes and Cygwin/MSYS2
+#   commands. The values are ultimately converted to Windows paths using slashes
+#   (i.e. C:/foo)
+# - $bindir and $libdir. These similarly contain the values specified for
+#   --bindir and --libdir, or defaults relative to $exec_prefix otherwise.
+#   Unlike --prefix, values specified to configure for --bindir and --libdir are
+#   assumed to be suitable for both native Windows processes and Cygwin/MSYS2.
+#   These two variables ultimately end up in Makefile.config as $(BINDIR) and
+#   $(LIBDIR) and are used for installation commands only.
+# - $ocaml_prefix, $ocaml_bindir and $ocaml_libdir are the _expanded_ values of
+#   $prefix, $bindir and $libdir so that the values can be inserted into OCaml
+#   strings (typically in utils/config.generated.ml). On Windows, these preserve
+#   the backslashes present in the value passed to --prefix.
+ocaml_bindir="$bindir"
+ocaml_libdir="$libdir"
+ocaml_prefix="$prefix"
+case $cygwin_build_env,$host in #(
+  true,*-w64-mingw32*|true,*-pc-windows) :
+    prefix="$(LC_ALL=C.UTF-8 cygpath -m "$prefix")"
+    if test "x${ocaml_prefix%%/*}" != "x$ocaml_prefix"
+then :
+  # $prefix contained a slash - normalise it with cygpath. The rationale for
+      # this allows both `./configure --prefix $PWD/install` (which will be a
+      # Cygwin path) and also systems lazily using slashes instead of
+      # backslashes (i.e. C:/Backslashes/Scare/Us) to work.
+      ocaml_prefix="$prefix"
+else $as_nop
+  # $prefix was using backslashes - preserve these in the build, but
+      # continue to use slashes for the Makefile variables.
+      if test "x$bindir" = 'x${exec_prefix}/bin'
+then :
+  ocaml_bindir='${exec_prefix}\bin'
+else $as_nop
+  ocaml_bindir="$bindir"
+fi
+      if test "x$libdir" = 'x${exec_prefix}/lib/ocaml'
+then :
+  ocaml_libdir='${exec_prefix}\lib\ocaml'
+else $as_nop
+  ocaml_libdir="$libdir"
+fi
+fi ;; #(
   *) :
      ;;
 esac
+
+if test x"$libdir_given" = 'xno'
+then :
+  if test x"$bindir_to_libdir" != 'x'
+then :
+  ocaml_libdir="$bindir_to_libdir"
+    target_libdir_is_relative=true
+    case $cygwin_build_env,$host in #(
+  true,*-w64-mingw32*|true,*-pc-windows) :
+    build_bindir_to_libdir="$(LC_ALL=C.UTF-8 cygpath \
+                                   "$bindir_to_libdir")" ;; #(
+  *) :
+    build_bindir_to_libdir="$bindir_to_libdir" ;;
+esac
+    case $build_bindir_to_libdir in #(
+  ./*) :
+    libdir="$bindir${build_bindir_to_libdir#.}" ;; #(
+  ../*) :
+    libdir="$bindir/$build_bindir_to_libdir" ;; #(
+  *) :
+    as_fn_error $? "--with-relative-libdir requires an explicit relative path" "$LINENO" 5 ;;
+esac
+fi
+else $as_nop
+  if test x"$bindir_to_libdir" != 'x'
+then :
+  as_fn_error $? "--with-relative-libdir and --libdir cannot both be specified" "$LINENO" 5
 fi
 fi
 
@@ -21044,6 +21458,88 @@ case $host in #(
      ;;
 esac
 
+# Determine the three Runtime IDs (see runtime/Mangling.md)
+
+
+
+
+
+# Bits 0-4 (dev + low 4 bits of release)
+
+
+# Bits 5-6 (high 2 bits of release)
+
+
+# Bits 7-9 (low 3 bits of reserved)
+quintet1="1 + $(expr \( $reserved_header_bits \* 4 \) % 32)"
+quintet1="$(echo '0123456789abcdefghijklmnopqrstuv' | cut -c $(expr \( $quintet1 \) + 1))"
+
+# Bits 10-11 (high 2 bits of reserved)
+quintet2_byte="$(echo '0123456789abcdefghijklmnopqrstuv' | cut -c $(expr \( $reserved_header_bits / 8 \) + 1))"
+
+# Bit 12 (no-flat-float-array)
+if $flat_float_array
+then :
+  quintet2_zinc='0'
+else $as_nop
+  quintet2_byte="4 + $quintet2_byte"
+  quintet2_zinc='4'
+fi
+# Bit 13 (fp)
+if $frame_pointers
+then :
+  quintet2_native="8 + $quintet2_byte"
+else $as_nop
+  quintet2_native="$quintet2_byte"
+fi
+# Bit 14 (tsan)
+if $tsan
+then :
+  quintet2_native="16 + $quintet2_native"
+fi
+
+quintet2_zinc="$(echo '0123456789abcdefghijklmnopqrstuv' | cut -c $(expr \( $quintet2_zinc \) + 1))"
+quintet2_byte="$(echo '0123456789abcdefghijklmnopqrstuv' | cut -c $(expr \( $quintet2_byte \) + 1))"
+quintet2_native="$(echo '0123456789abcdefghijklmnopqrstuv' | cut -c $(expr \( $quintet2_native \) + 1))"
+
+# Bit 15 (int31)
+if $arch64
+then :
+  quintet3_zinc='0'
+else $as_nop
+  quintet3_zinc='1'
+fi
+# Bit 16 (static)
+if ! $supports_shared_libraries
+then :
+  quintet3_zinc="2 + $quintet3_zinc"
+fi
+# Bit 17 (no-compression)
+if test x"$zstd_status" != 'xok'
+then :
+  quintet3_zinc="4 + $quintet3_zinc"
+fi
+# Bit 18 (ansi)
+case $target,$windows_unicode in #(
+  *-*-mingw32,0|*-pc-windows,0) :
+    quintet3="8 + $quintet3_zinc" ;; #(
+  *) :
+    quintet3="$quintet3_zinc" ;;
+esac
+# Bit 19 (mutable-string) cannot be set since OCaml 5.0
+
+quintet3_zinc="$(echo '0123456789abcdefghijklmnopqrstuv' | cut -c $(expr \( $quintet3_zinc \) + 1))"
+quintet3="$(echo '0123456789abcdefghijklmnopqrstuv' | cut -c $(expr \( $quintet3 \) + 1))"
+
+zinc_runtime_id="71${quintet2_zinc}${quintet3_zinc}"
+bytecode_runtime_id="7${quintet1}${quintet2_byte}${quintet3}"
+native_runtime_id="7${quintet1}${quintet2_native}${quintet3}"
+
+# Update the values for is_official_release and release_number in
+# utils/config.common.ml.in (this is done when tools/autogen is run, not each
+# time configure is run!)
+
+
 # Do not permanently cache the result of flexdll.h
 unset ac_cv_header_flexdll_h
 
@@ -21051,6 +21547,10 @@ unset ac_cv_header_flexdll_h
 # (this is needed for the OCaml configuration module)
 
 
+# Create ld.conf
+ac_config_commands="$ac_config_commands runtime/ld.conf"
+
+
 # Just before config.status is generated, determine the final values for MKEXE,
 # MKDLL, MKMAINDLL and MKEXE_VIA_CC. The final variables controlling these are:
 # $mkexe - the linking command and munged CFLAGS + any extra flexlink flags
@@ -21195,6 +21695,7 @@ cclibs="$cclibs $mathlib $DLLIBS $PTHREAD_LIBS"
 
   saved_exec_prefix="$exec_prefix"
   saved_prefix="$prefix"
+  prefix="$ocaml_prefix"
   if test "x$prefix" = "xNONE"
 then :
   prefix="$ac_default_prefix"
@@ -21204,15 +21705,42 @@ then :
   exec_prefix="$prefix"
 fi
   eval "exec_prefix=\"$exec_prefix\""
-  eval "ocaml_bindir=\"$bindir\""
-  eval "ocaml_libdir=\"$libdir\""
-  if test x"$target_bindir" = 'x'
+  # Set variables necessary to create utils/config.generated.ml.
+  # $HOST_BINDIR is always the absolute path to the binary directory, in host
+  #   format (i.e. potentially with backslashes on Windows).
+  # $TARGET_BINDIR can be specified by the caller when building cross-compilers,
+  #   and the value then is used unaltered. Otherwise, $TARGET_BINDIR is set to
+  #   '.' when the compiler is configured with --with-relative-libdir or the
+  #   value of $HOST_BINDIR otherwise.
+  # $ocaml_bindir is used in utils/config.generated.ml and is _empty_ if the
+  #   compiler is configured with --with-relative-libdir (otherwise the path
+  #   would be embedded in config.cmo)
+  eval "HOST_BINDIR=\"$ocaml_bindir\""
+  if test "x$bindir_to_libdir" = 'x'
 then :
-  target_bindir="$ocaml_bindir"
+  ocaml_bindir="$HOST_BINDIR"
+else $as_nop
+  ocaml_bindir=''
 fi
-  if test x"$target_launch_method" = 'x'
+  if test x"$TARGET_BINDIR" = 'x'
+then :
+  if test "x$bindir_to_libdir" = 'x'
 then :
-  target_launch_method="$launch_method"
+  TARGET_BINDIR="$HOST_BINDIR"
+else $as_nop
+  TARGET_BINDIR='.'
+fi
+fi
+  eval "ocaml_libdir=\"$ocaml_libdir\""
+  if test "x$bindir_to_libdir" = 'x'
+then :
+  TARGET_LIBDIR="$ocaml_libdir"
+else $as_nop
+  TARGET_LIBDIR="$bindir_to_libdir"
+fi
+  if test x"$launch_method_target" = 'x'
+then :
+  launch_method_target="$launch_method"
 fi
   prefix="$saved_prefix"
   exec_prefix="$saved_exec_prefix"
@@ -21691,7 +22219,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by OCaml $as_me 5.3.1+dev0-2025-01-06, which was
+This file was extended by OCaml $as_me 5.3.1+relocatable, which was
 generated by GNU Autoconf 2.71.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -21764,7 +22292,7 @@ ac_cs_config_escaped=`printf "%s\n" "$ac_cs_config" | sed "s/^ //; s/'/'\\\\\\\\
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config='$ac_cs_config_escaped'
 ac_cs_version="\\
-OCaml config.status 5.3.1+dev0-2025-01-06
+OCaml config.status 5.3.1+relocatable
 configured by $0, generated by GNU Autoconf 2.71,
   with options \\"\$ac_cs_config\\"
 
@@ -22167,11 +22695,11 @@ fi
 
 
 
-  launch_method='$(echo "$launch_method" | sed -e "s/'/'\"'\"'/g")'
-  target_launch_method=\
-'$(echo "$target_launch_method" | sed -e "s/'/'\"'\"'/g")'
-  ocaml_bindir='$(echo "$ocaml_bindir" | sed -e "s/'/'\"'\"'/g")'
-  target_bindir='$(echo "$target_bindir" | sed -e "s/'/'\"'\"'/g")'
+ocaml_additional_stublibs_dir=\
+'$(echo "$ocaml_additional_stublibs_dir" | sed -e "s/'/'\"'\"'/g")'
+  ocaml_libdir='$(echo "$ocaml_libdir" | sed -e "s/'/'\"'\"'/g")'
+  default_separator='$default_separator'
+  supports_shared_libraries='$supports_shared_libraries'
 
 _ACEOF
 
@@ -22184,8 +22712,6 @@ do
     "Makefile.build_config") CONFIG_FILES="$CONFIG_FILES Makefile.build_config" ;;
     "Makefile.config") CONFIG_FILES="$CONFIG_FILES Makefile.config" ;;
     "stdlib/sys.ml") CONFIG_FILES="$CONFIG_FILES stdlib/sys.ml" ;;
-    "manual/src/version.tex") CONFIG_FILES="$CONFIG_FILES manual/src/version.tex" ;;
-    "manual/src/html_processing/src/common.ml") CONFIG_FILES="$CONFIG_FILES manual/src/html_processing/src/common.ml" ;;
     "ocamltest/ocamltest_config.ml") CONFIG_FILES="$CONFIG_FILES ocamltest/ocamltest_config.ml" ;;
     "otherlibs/dynlink/dynlink_config.ml") CONFIG_FILES="$CONFIG_FILES otherlibs/dynlink/dynlink_config.ml" ;;
     "utils/config.common.ml") CONFIG_FILES="$CONFIG_FILES utils/config.common.ml" ;;
@@ -22193,12 +22719,15 @@ do
     "runtime/caml/exec.h") CONFIG_HEADERS="$CONFIG_HEADERS runtime/caml/exec.h" ;;
     "runtime/caml/m.h") CONFIG_HEADERS="$CONFIG_HEADERS runtime/caml/m.h" ;;
     "runtime/caml/s.h") CONFIG_HEADERS="$CONFIG_HEADERS runtime/caml/s.h" ;;
+    "runtime/sys_int.h") CONFIG_HEADERS="$CONFIG_HEADERS runtime/sys_int.h" ;;
     "runtime/caml/version.h") CONFIG_HEADERS="$CONFIG_HEADERS runtime/caml/version.h" ;;
     "compilerlibs/META") CONFIG_FILES="$CONFIG_FILES compilerlibs/META" ;;
     "otherlibs/dynlink/META") CONFIG_FILES="$CONFIG_FILES otherlibs/dynlink/META" ;;
     "otherlibs/runtime_events/META") CONFIG_FILES="$CONFIG_FILES otherlibs/runtime_events/META" ;;
     "stdlib/META") CONFIG_FILES="$CONFIG_FILES stdlib/META" ;;
     "testsuite/tools/toolchain.ml") CONFIG_FILES="$CONFIG_FILES testsuite/tools/toolchain.ml" ;;
+    "manual/src/version.tex") CONFIG_FILES="$CONFIG_FILES manual/src/version.tex" ;;
+    "manual/src/html_processing/src/common.ml") CONFIG_FILES="$CONFIG_FILES manual/src/html_processing/src/common.ml" ;;
     "native-symlinks") CONFIG_COMMANDS="$CONFIG_COMMANDS native-symlinks" ;;
     "ocamldoc/META") CONFIG_FILES="$CONFIG_FILES ocamldoc/META" ;;
     "libtool") CONFIG_COMMANDS="$CONFIG_COMMANDS libtool" ;;
@@ -22208,9 +22737,9 @@ do
     "otherlibs/unix/META") CONFIG_FILES="$CONFIG_FILES otherlibs/unix/META" ;;
     "otherlibs/unix/unix.ml") CONFIG_LINKS="$CONFIG_LINKS otherlibs/unix/unix.ml:otherlibs/unix/unix_${unix_or_win32}.ml" ;;
     "otherlibs/str/META") CONFIG_FILES="$CONFIG_FILES otherlibs/str/META" ;;
-    "shebang") CONFIG_COMMANDS="$CONFIG_COMMANDS shebang" ;;
     "otherlibs/systhreads/META") CONFIG_FILES="$CONFIG_FILES otherlibs/systhreads/META" ;;
     "ocamltest/ocamltest_unix.ml") CONFIG_LINKS="$CONFIG_LINKS ocamltest/ocamltest_unix.ml:${ocamltest_unix_mod}" ;;
+    "runtime/ld.conf") CONFIG_COMMANDS="$CONFIG_COMMANDS runtime/ld.conf" ;;
 
   *) as_fn_error $? "invalid argument: \`$ac_config_target'" "$LINENO" 5;;
   esac
@@ -23341,10 +23870,13 @@ ltmain=$ac_aux_dir/ltmain.sh
   chmod +x "$ofile"
 
  ;;
-    "shebang":C) printf '%s\n%s\000\n' "$launch_method" "$ocaml_bindir" \
-    > stdlib/runtime.info
-  printf '%s\n%s\000\n' "$target_launch_method" "$target_bindir" \
-    > stdlib/target_runtime.info ;;
+    "runtime/ld.conf":C) rm -f runtime/ld.conf
+  test x"$ocaml_additional_stublibs_dir" = 'x' || \
+    echo "$ocaml_additional_stublibs_dir" > runtime/ld.conf
+  if $supports_shared_libraries; then
+    echo ".${default_separator}stublibs" >> runtime/ld.conf
+  fi
+  echo "." >> runtime/ld.conf ;;
 
   esac
 done # for ac_tag
diff --git a/configure.ac b/configure.ac
index a1ce09dc58bf..b3deb70abec6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,6 +25,26 @@ AC_INIT([OCaml],
 
 AC_MSG_NOTICE([Configuring OCaml version AC_PACKAGE_VERSION])
 
+# It's important for the setting up of defaults and the checking of the
+# --with-relative-libdir option to know whether the user specified --libdir.
+# Unfortunately, autoconf doesn't provide an easy way to determine this, so we
+# simply repeat autoconf's argument parsing for the libdir and mandir options.
+# This is done early in the script to ensure that only autoconf and site-config
+# scripts have run.
+libdir_given=no
+mandir_given=no
+for ac_arg
+do
+  case $ac_arg in
+    -mandir=* | --mandir=* | --mandi=* | --mand=* | --man=* | --ma=* | --m=* | \
+    -mandir | --mandir | --mandi | --mand | --man | --ma | --m)
+      mandir_given=yes;;
+    -libdir=* | --libdir=* | --libdi=* | --libd=* | \
+    -libdir   | --libdir   | --libdi   | --libd)
+      libdir_given=yes;;
+  esac
+done
+
 # Configuration variables
 
 ## Command-line arguments passed to configure
@@ -83,6 +103,12 @@ ocamltest_libunix=None
 ocamltest_unix_impl="dummy"
 unix_library=""
 unix_directory=""
+target_libdir_is_relative=false
+srcdir_abs=''
+srcdir_abs_real=''
+build_map_flags=''
+runtime_search=''
+runtime_search_target=''
 
 # Information about the package
 
@@ -105,6 +131,7 @@ AC_SUBST([OCAML_VERSION_MINOR], [OCAML__VERSION_MINOR])
 AC_SUBST([OCAML_VERSION_PATCHLEVEL], [OCAML__VERSION_PATCHLEVEL])
 AC_SUBST([OCAML_VERSION_EXTRA], [OCAML__VERSION_EXTRA])
 AC_SUBST([OCAML_VERSION_SHORT], [OCAML__VERSION_SHORT])
+AC_SUBST([OCAML_RELEASE_NUMBER], [OCAML__RELEASE_NUMBER])
 AC_DEFINE([MAGIC_NUMBER_PREFIX], ["][MAGIC_NUMBER__PREFIX]["])
 AC_DEFINE([MAGIC_NUMBER_VERSION], ["][MAGIC_NUMBER__VERSION]["])
 AC_DEFINE([EXEC_MAGIC_LENGTH], [MAGIC_NUMBER__LENGTH])
@@ -184,6 +211,8 @@ AC_SUBST([flexdll_dir])
 AC_SUBST([winpthreads_source_dir])
 AC_SUBST([winpthreads_source_include_dir])
 AC_SUBST([shebangscripts])
+AC_SUBST([launch_method])
+AC_SUBST([launch_method_target])
 AC_SUBST([AR])
 AC_SUBST([mklib])
 AC_SUBST([supports_shared_libraries])
@@ -210,6 +239,7 @@ AC_SUBST([unix_library])
 AC_SUBST([unix_directory])
 AC_SUBST([cc_has_debug_prefix_map])
 AC_SUBST([as_has_debug_prefix_map])
+AC_SUBST([as_is_cc])
 AC_SUBST([with_debugger]) # TODO: rename this variable
 AC_SUBST([build_ocamldebug])
 AC_SUBST([build_ocamltex])
@@ -253,18 +283,29 @@ AC_SUBST([flexdll_chain])
 AC_SUBST([PACKLD])
 AC_SUBST([build_libraries_manpages])
 AC_SUBST([compute_deps])
+AC_SUBST([ocaml_prefix])
 AC_SUBST([ocaml_bindir])
+AC_SUBST([TARGET_BINDIR])
 AC_SUBST([ocaml_libdir])
+AC_SUBST([TARGET_LIBDIR])
 AC_SUBST([QS])
 AC_SUBST([ar_supports_response_files])
+AC_SUBST([target_libdir_is_relative])
+AC_SUBST([srcdir_abs])
+AC_SUBST([srcdir_abs_real])
+AC_SUBST([build_map_flags])
+AC_SUBST([zinc_runtime_id])
+AC_SUBST([bytecode_runtime_id])
+AC_SUBST([native_runtime_id])
+AC_SUBST([suffixing])
+AC_SUBST([runtime_search])
+AC_SUBST([runtime_search_target])
 
 ## Generated files
 
 AC_CONFIG_FILES([Makefile.build_config])
 AC_CONFIG_FILES([Makefile.config])
 AC_CONFIG_FILES([stdlib/sys.ml])
-AC_CONFIG_FILES([manual/src/version.tex])
-AC_CONFIG_FILES([manual/src/html_processing/src/common.ml])
 AC_CONFIG_FILES([ocamltest/ocamltest_config.ml])
 AC_CONFIG_FILES([otherlibs/dynlink/dynlink_config.ml])
 AC_CONFIG_FILES([utils/config.common.ml])
@@ -272,12 +313,16 @@ AC_CONFIG_FILES([utils/config.generated.ml])
 AC_CONFIG_HEADERS([runtime/caml/exec.h])
 AC_CONFIG_HEADERS([runtime/caml/m.h])
 AC_CONFIG_HEADERS([runtime/caml/s.h])
+AC_CONFIG_HEADERS([runtime/sys_int.h])
 AC_CONFIG_HEADERS([runtime/caml/version.h])
 AC_CONFIG_FILES([compilerlibs/META])
 AC_CONFIG_FILES([otherlibs/dynlink/META])
 AC_CONFIG_FILES([otherlibs/runtime_events/META])
 AC_CONFIG_FILES([stdlib/META])
 AC_CONFIG_FILES([testsuite/tools/toolchain.ml])
+AS_IF([test -d manual],
+  [AC_CONFIG_FILES([manual/src/version.tex])
+  AC_CONFIG_FILES([manual/src/html_processing/src/common.ml])])
 
 # Definitions related to the version of OCaml
 AC_DEFINE([OCAML_VERSION_MAJOR], [OCAML__VERSION_MAJOR])
@@ -288,6 +333,7 @@ m4_if([OCAML__VERSION_EXTRA],[], [],
   AC_DEFINE([OCAML_VERSION_EXTRA], ["][OCAML__VERSION_EXTRA]["])])
 AC_DEFINE([OCAML_VERSION], [OCAML__VERSION_NUMBER])
 AC_DEFINE([OCAML_VERSION_STRING], ["][OCAML__VERSION]["])
+AC_DEFINE([OCAML_RELEASE_NUMBER], [OCAML__RELEASE_NUMBER])
 
 # Works out how many "o"s are needed in quoted strings
 AC_CONFIG_COMMANDS_PRE(OCAML_QUOTED_STRING_ID)
@@ -298,12 +344,45 @@ AC_CANONICAL_BUILD
 AC_CANONICAL_HOST
 AC_CANONICAL_TARGET
 
+# $cygwin_build_env=true if the build is taking place in any kind of Cygwin-like
+# environment (which may include cross-compiling _from_ Cygwin)
+# All patterns end with * (cf. build-aux/config.sub)
+#
+# In Cygwin itself, the mingw-w64 compilers are cross-compilers
+# (host=x86_64-pc-cygwin; target=*-w64-mingw32) and $build when running from
+# within Cygwin is always *-pc-cygwin.
+#
+# In MSYS2, the mingw-w64 compilers are normal host compilers, which MSYS2 makes
+# available through different Environments (similar to the Microsoft Visual
+# Studio Tools Command Prompts; see https://www.msys2.org/docs/environments/).
+# It is possible to use MSYS2's "Cygwin" gcc (the equivalent of compiling native
+# Cygwin), in which case $build is *-*-cygwin (some older MSYS2 installations
+# may report the legacy *-*-msys*)
+# The mingw-w64 Environments manually set $build to *-w64-mingw32, but the
+# _native_ value inferred by config.guess (which uses uname -s) will be
+# *-pc-mingw32 (for the 32-bit _target_ environments, even though MSYS2 is a
+# 64-bit build environment) and *-pc-mingw64 (for the 64-bit _target_
+# environments).
+#
+# This leads to the four patterns below, all of which imply that the build is
+# taking place on a system where Cygwin's utilities (cygpath, etc.) can be
+# expected to be found and its semantics (CYGWIN=winsymlinks:native, etc.) be
+# expected to apply.
+#
+# Note that although build=x86_64-pc-mingw64 will be accepted here, it is highly
+# likely that that's a misconfigured environment, and the script will
+# subsequently fail if host has not been altered to x86_64-w64-mingw32.
+AS_CASE([$build],
+  [*-*-cygwin*|*-*-msys*|*-*-mingw32*|*-*-mingw64*],
+    [cygwin_build_env=true],
+  [cygwin_build_env=false])
+
 # Ensure that AC_CONFIG_LINKS will either create symlinks which are compatible
 # with native Windows (i.e. NTFS symlinks, not WSL or Cygwin-emulated ones) or
 # use its fallback mechanisms. Native Windows versions of ocamlc/ocamlopt cannot
 # interpret either WSL or Cygwin-emulated symlinks.
-AS_CASE([$host],
-  [*-pc-windows|*-w64-mingw32*],
+AS_CASE([$cygwin_build_env,$host],
+  [true,*-pc-windows|true,*-w64-mingw32*],
     [AC_CONFIG_COMMANDS([native-symlinks], [],
       [export CYGWIN="\$CYGWIN\${CYGWIN:+ }winsymlinks:nativestrict"
       export MSYS="\$MSYS\${MSYS:+ }winsymlinks:nativestrict"])])
@@ -341,6 +420,17 @@ AS_IF([test -n "$csc"],
       AS_CASE([$host_cpu], [i*86], [CSCFLAGS="$CSCFLAGS /platform:x86"])],
     [AC_MSG_WARN([Mono is not yet supported - C sharp tests disabled])])])
 
+# Environment-specific set-up
+
+dnl The separator should be being treated differently for host/target for
+dnl cross-compilers, but the installation layout for cross-compilers is already
+dnl incorrect (for example, ld.conf is processed by _both_ the host and target
+dnl runtimes), so this is left as target-specific for now.
+AS_CASE([$target],
+  [*-w64-mingw32*|*-pc-windows],
+    [default_separator='\'],
+  [default_separator='/'])
+
 # Environment variables that are taken into account
 
 AC_ARG_VAR([AS], [which assembler to use])
@@ -511,16 +601,27 @@ AC_ARG_ENABLE([cmm-invariants],
 AC_ARG_WITH([target-bindir],
   [AS_HELP_STRING([--with-target-bindir],
     [location of the runtime binaries on the target system])],
-  [target_bindir=$withval],
-  [target_bindir=''])
+  [TARGET_BINDIR=$withval],
+  [TARGET_BINDIR=''])
 
 AC_ARG_WITH([target-sh],
   [AS_HELP_STRING([--with-target-sh],
     [location of Posix sh on the target system])],
   [AS_IF([test x"$withval" = 'xno'],
-    [target_launch_method='exe'],
-    [target_launch_method="$withval"])],
-  [target_launch_method=''])
+    [launch_method_target='exe'],
+    [launch_method_target="$withval"])],
+  [launch_method_target=''])
+
+AC_ARG_WITH([additional-stublibsdir],
+  [AS_HELP_STRING([--with-additional-stublibsdir],
+    [additional directory for searching for bytecode stub libraries])],
+  [AS_CASE([$withval],
+    [no],
+      [ocaml_additional_stublibs_dir=''],
+    [yes],
+      [ocaml_additional_stublibs_dir="..${default_separator}stublibs"],
+    [ocaml_additional_stublibs_dir="$withval"])],
+  [ocaml_additional_stublibs_dir=''])
 
 AC_ARG_ENABLE([reserved-header-bits],
   [AS_HELP_STRING([--enable-reserved-header-bits=BITS],
@@ -566,6 +667,52 @@ AC_ARG_ENABLE([mmap-map-stack],
   [AS_HELP_STRING([--enable-mmap-map-stack],
     [use mmap to allocate stacks instead of malloc])])
 
+AC_ARG_WITH([relative-libdir],
+  [AS_HELP_STRING([--with-relative-libdir],
+    m4_normalize([location of the Standard Library, specified relative to
+       --bindir (if no argument is given to --with-relative-libdir, defaults to
+       ../lib/ocaml)]))],
+  [AS_CASE([$withval],
+    [no],
+      [bindir_to_libdir=''],
+    [yes],
+      [bindir_to_libdir="..${default_separator}lib${default_separator}ocaml"],
+    [bindir_to_libdir="$withval"])],
+  [bindir_to_libdir=''])
+
+AC_ARG_ENABLE([suffixing],
+  [AS_HELP_STRING([--disable-suffixing],
+    [disable suffixing of runtime executables and shared libraries])],
+  [AS_IF([test "x$enableval" = 'xno'], [suffixing=false], [suffixing=true])],
+  [suffixing=auto])
+
+AC_ARG_ENABLE([runtime-search],
+  [AS_HELP_STRING([--enable-runtime-search],
+    [allow the distribution's bytecode executables to search for ocamlrun])],
+  [AS_CASE([$enableval],
+    [no],[],
+    [yes],[runtime_search='enable'],
+    [fallback],[runtime_search='fallback'],
+    [AC_MSG_ERROR(m4_normalize([valid values are yes, no or fallback for
+       --enable-runtime-search]))])])
+
+AC_ARG_ENABLE([runtime-search-target],
+  [AS_HELP_STRING([--enable-runtime-search-target],
+    [allow bytecode executables produced by ocamlc to search for ocamlrun])],
+  [AS_CASE([$enableval],
+    [no],[],
+    [yes],[runtime_search_target='enable'],
+    [fallback],[runtime_search_target='fallback'],
+    [AC_MSG_ERROR(m4_normalize([valid values are yes, no or fallback for
+       --enable-runtime-search-target]))])])
+
+AS_CASE([$suffixing,$runtime_search,$runtime_search_target],
+  [true,*,*|false,,],[],
+  [auto,,],[suffixing=false],
+  [auto,*,*],[suffixing=true],
+  [false,*,*],[AC_MSG_ERROR(m4_normalize([--disable-suffixed cannot be used with
+       --enable-runtime-search or --enable-runtime-search-target]))])
+
 AC_ARG_WITH([afl],
   [AS_HELP_STRING([--with-afl],
     [use the AFL fuzzer])])
@@ -713,8 +860,8 @@ AS_CASE([$ocaml_cc_vendor],
 # See https://lists.gnu.org/archive/html/autoconf/2019-07/msg00002.html
 # for the detailed explanation.
 
-ocamlsrcdir=$(unset CDPATH; cd -- "$srcdir" && printf %sX "$PWD") || fail
-ocamlsrcdir=${ocamlsrcdir%X}
+srcdir_abs=$(unset CDPATH; cd -- "$srcdir" && printf %sX "$PWD") || fail
+srcdir_abs=${srcdir_abs%X}
 
 # Whether ar supports @FILE arguments
 
@@ -724,16 +871,17 @@ AS_CASE([$lt_cv_ar_at_file],
 
 # Libraries to build depending on the host
 
-AS_CASE([$host],
-  [*-*-mingw32*|*-pc-windows],
+AS_CASE([$cygwin_build_env,$host],
+  [true,*-*-mingw32*|true,*-pc-windows],
     [unix_or_win32="win32"
-    ln='cp -pf'
+    OCAML_CHECK_LN_ON_WINDOWS
     ocamltest_libunix="Some false"
-    ocamlsrcdir="$(LC_ALL=C.UTF-8 cygpath -w -- "$ocamlsrcdir")"
+    ocamlsrcdir="$(LC_ALL=C.UTF-8 cygpath -w -- "$srcdir_abs")"
     ocamlyacc_wstr_module="yacc/wstr"],
   [unix_or_win32="unix"
   ln='ln -sf'
   ocamltest_libunix="Some true"
+  ocamlsrcdir="$srcdir_abs"
   ocamlyacc_wstr_module=""])
 
 AS_CASE([$host],
@@ -789,39 +937,14 @@ AS_IF([test "x$interpval" = "xyes"],
       # not use shebang scripts
       shebangscripts=true
       launch_method='sh'
-      AS_IF([test x"$target_launch_method" = 'x'],
-        [target_launch_method='exe'])],
+      AS_IF([test x"$launch_method_target" = 'x'],
+        [launch_method_target='exe'])],
     [*-*-mingw32*|*-pc-windows], [],
     [shebangscripts=true
     launch_method='sh']
   )]
 )
 
-# stdlib/runtime.info and stdlib/target_runtime.info are generated by commands
-# in config.status, rather than by the .in mechanism, since the latter cannot
-# reliably process binary files.
-AC_CONFIG_COMMANDS([shebang],
-  [printf '%s\n%s\000\n' "$launch_method" "$ocaml_bindir" \
-    > stdlib/runtime.info
-  printf '%s\n%s\000\n' "$target_launch_method" "$target_bindir" \
-    > stdlib/target_runtime.info],
-dnl These declarations are put in a here-document in configure, so the command
-dnl in '$(...)' _is_ evaluated as the content is written to config.status (by
-dnl standard interpretation of a here-document). The sed commands quote any
-dnl nefarious single quotes which may appear in any of the strings.
-  [launch_method='$(echo "$launch_method" | sed -e "s/'/'\"'\"'/g")'
-  target_launch_method=\
-'$(echo "$target_launch_method" | sed -e "s/'/'\"'\"'/g")'
-  ocaml_bindir='$(echo "$ocaml_bindir" | sed -e "s/'/'\"'\"'/g")'
-  target_bindir='$(echo "$target_bindir" | sed -e "s/'/'\"'\"'/g")'])
-
-# Are we building a cross-compiler
-
-AS_IF(
-  [test x"$host" = x"$target"],
-    [cross_compiler=false],
-    [cross_compiler=true])
-
 # Checks for programs
 
 ## Check for the C compiler: done by libtool
@@ -1035,12 +1158,13 @@ AS_IF([test x"$supports_shared_libraries" != 'xfalse'], [
     # ensure it can be executed from a native Windows process. The check
     # is only necessary when cross-compiling.
     AS_IF([test x"$build" != x"$host"],[
-      AS_CASE([$build],
-        [*-pc-msys|*-pc-cygwin*],
-          [flexlink_where="$(cmd /c "$flexlink" -where 2>/dev/null)"
-          AS_IF([test -z "$flexlink_where"],
-            [AC_MSG_ERROR(m4_normalize([$flexlink is not executable from a
-            native Win32 process]))])])
+      AS_IF([$cygwin_build_env],
+        [flexlink_where="$(cmd /c "$flexlink" -where 2>/dev/null)"
+        AS_IF([test -z "$flexlink_where"],
+          [AC_MSG_ERROR(m4_normalize([$flexlink is not executable from a
+          native Win32 process]))
+        ])
+      ])
     ])
   ])
 
@@ -1172,6 +1296,7 @@ AS_CASE([$host],
   [AC_CHECK_HEADERS([unistd.h],[AC_DEFINE([HAS_UNISTD], [1])])])
 
 AC_CHECK_HEADER([math.h])
+AC_CHECK_HEADER([libgen.h],[AC_DEFINE([HAS_LIBGEN_H], [1])])
 AC_CHECK_HEADER([pthread_np.h],[AC_DEFINE([HAS_PTHREAD_NP_H], [1])])
 AC_CHECK_HEADER([dirent.h], [AC_DEFINE([HAS_DIRENT], [1])], [],
   [#include <sys/types.h>])
@@ -1637,24 +1762,33 @@ AS_IF([test -n "$target_alias"],
 # to avoiding forking a C compiler process for each compilation by ocamlopt.
 # Both AS and ASPP can be overridden by the user.
 
-default_as="$CC -c"
-default_aspp="$CC -c"
+as_is_cc=true
+default_as=''
 
 AS_CASE([$as_target,$ocaml_cc_vendor],
   [*-*-linux*,gcc-*],
     [AS_CASE([$as_cpu],
       [x86_64|arm*|aarch64*|i[[3-6]]86|riscv*],
-        [default_as="${toolpref}as"])],
+        [default_as="${toolpref}as"
+        as_is_cc=false])],
+  [*-*-cygwin,gcc-*],
+    [default_as="${toolpref}as"
+    as_is_cc=false],
   [i686-pc-windows,*],
     [default_as="ml -nologo -coff -Cp -c -Fo"
-    default_aspp="$default_as"],
+    default_aspp="$default_as"
+    as_is_cc=false],
   [x86_64-pc-windows,*],
     [default_as="ml64 -nologo -Cp -c -Fo"
-    default_aspp="$default_as"],
+    default_aspp="$default_as"
+    as_is_cc=false],
   [*-*-darwin*,clang-*],
-    [default_as="$default_as -Wno-trigraphs"
+    [default_as="$CC -c -Wno-trigraphs"
     default_aspp="$default_as"])
 
+AS_IF([test -z "$default_as"],[default_as="$CC -c"])
+AS_IF([test -z "$default_aspp"],[default_aspp="$CC -c"])
+
 AS_IF([test "$with_pic"],
   [fpic=true
   AC_DEFINE([CAML_WITH_FPIC], [1])
@@ -1714,6 +1848,9 @@ AC_CHECK_FUNC([getrusage], [AC_DEFINE([HAS_GETRUSAGE], [1])])
 ## times
 AC_CHECK_FUNC([times], [AC_DEFINE([HAS_TIMES], [1])])
 
+## strlcpy
+AC_CHECK_FUNC([strlcpy], [AC_DEFINE([HAS_STRLCPY], [1])])
+
 ## secure_getenv and __secure_getenv
 
 saved_CPPFLAGS="$CPPFLAGS"
@@ -2204,7 +2341,6 @@ AC_CHECK_FUNC([pwrite], [AC_DEFINE([HAS_PWRITE], [1])])
 
 ## -fdebug-prefix-map support by the C compiler
 AS_CASE([$ocaml_cc_vendor,$host],
-  [*,*-*-mingw32*], [cc_has_debug_prefix_map=false],
   [*,*-pc-windows], [cc_has_debug_prefix_map=false],
   [xlc*,powerpc-ibm-aix*], [cc_has_debug_prefix_map=false],
   [sunc*,sparc-sun-*], [cc_has_debug_prefix_map=false],
@@ -2212,6 +2348,20 @@ AS_CASE([$ocaml_cc_vendor,$host],
     [cc_has_debug_prefix_map=true], [cc_has_debug_prefix_map=false],
     [$warn_error_flag])])
 
+## -ffile-prefix-map support by the C compiler - used in the build, not by
+## the compiler
+AS_IF([test x"$bindir_to_libdir" != 'x'],
+  [srcdir_abs_real="$(realpath "$srcdir_abs" 2>/dev/null)"
+  AS_IF([test x"$srcdir_abs_real" = "x$srcdir_abs"],
+    [srcdir_abs_real=''])
+  AX_CHECK_COMPILE_FLAG([-Wa,--debug-prefix-map=old=new],
+    [build_map_flags='-Wa,--debug-prefix-map='], [], [$warn_error_flag])
+  AX_CHECK_COMPILE_FLAG([-ffile-prefix-map=old=new],
+    [build_map_flags="$build_map_flags -ffile-prefix-map="],
+    [AS_IF([$cc_has_debug_prefix_map],
+      [build_map_flags="$build_map_flags -fdebug-prefix-map="])],
+    [$warn_error_flag])])
+
 ## Does stat support nanosecond precision
 
 stat_has_ns_precision=false
@@ -2656,10 +2806,10 @@ shlwapi.lib synchronization.lib"])
 
 AC_CONFIG_COMMANDS_PRE([cclibs="$cclibs $mathlib $DLLIBS $PTHREAD_LIBS"])
 
-AS_IF([test x"$libdir" = x'${exec_prefix}/lib'],
+AS_IF([test x"$libdir_given" = 'xno'],
   [libdir="$libdir"/ocaml])
 
-AS_IF([test x"$mandir" = x'${datarootdir}/man'],
+AS_IF([test x"$mandir_given" = 'xno'],
   [mandir='${prefix}/man'])
 
 # Define default prefix correctly for the different Windows ports
@@ -2668,11 +2818,65 @@ AS_IF([test x"$prefix" = "xNONE"],
     [i686-w64-mingw32*], [prefix='C:/ocamlmgw'],
     [x86_64-w64-mingw32*], [prefix='C:/ocamlmgw64'],
     [i686-pc-windows], [prefix='C:/ocamlms'],
-    [x86_64-pc-windows], [prefix='C:/ocamlms64'])],
-  [AS_IF([test x"$unix_or_win32" = "xwin32" \
-          && test "$host_vendor-$host_os" != "$build_vendor-$build_os" ],
-    [AS_CASE([$build],
-      [*-pc-cygwin], [prefix="$(LC_ALL=C.UTF-8 cygpath -m "$prefix")"])])])
+    [x86_64-pc-windows], [prefix='C:/ocamlms64'])])
+
+# Normalise $prefix, if necessary, on Windows. There are 7 variables to be
+# considered:
+# - $prefix and $exec_prefix. These are autoconf variables containing the values
+#   specified for --prefix and --exec-prefix respectively, or NONE if these
+#   flags were not given on the command line. These two variables are written to
+#   Makefile.config and are in _build_ format. On native Windows, the values
+#   must be suitable to pass to _both_ native Windows processes and Cygwin/MSYS2
+#   commands. The values are ultimately converted to Windows paths using slashes
+#   (i.e. C:/foo)
+# - $bindir and $libdir. These similarly contain the values specified for
+#   --bindir and --libdir, or defaults relative to $exec_prefix otherwise.
+#   Unlike --prefix, values specified to configure for --bindir and --libdir are
+#   assumed to be suitable for both native Windows processes and Cygwin/MSYS2.
+#   These two variables ultimately end up in Makefile.config as $(BINDIR) and
+#   $(LIBDIR) and are used for installation commands only.
+# - $ocaml_prefix, $ocaml_bindir and $ocaml_libdir are the _expanded_ values of
+#   $prefix, $bindir and $libdir so that the values can be inserted into OCaml
+#   strings (typically in utils/config.generated.ml). On Windows, these preserve
+#   the backslashes present in the value passed to --prefix.
+ocaml_bindir="$bindir"
+ocaml_libdir="$libdir"
+ocaml_prefix="$prefix"
+AS_CASE([$cygwin_build_env,$host],
+  [true,*-w64-mingw32*|true,*-pc-windows],
+    [prefix="$(LC_ALL=C.UTF-8 cygpath -m "$prefix")"
+    AS_IF([test "x${ocaml_prefix%%/*}" != "x$ocaml_prefix"],
+      # $prefix contained a slash - normalise it with cygpath. The rationale for
+      # this allows both `./configure --prefix $PWD/install` (which will be a
+      # Cygwin path) and also systems lazily using slashes instead of
+      # backslashes (i.e. C:/Backslashes/Scare/Us) to work.
+      [ocaml_prefix="$prefix"],
+      # $prefix was using backslashes - preserve these in the build, but
+      # continue to use slashes for the Makefile variables.
+      [AS_IF([test "x$bindir" = 'x${exec_prefix}/bin'],
+        [ocaml_bindir='${exec_prefix}\bin'],
+        [ocaml_bindir="$bindir"])
+      AS_IF([test "x$libdir" = 'x${exec_prefix}/lib/ocaml'],
+        [ocaml_libdir='${exec_prefix}\lib\ocaml'],
+        [ocaml_libdir="$libdir"])])])
+
+AS_IF([test x"$libdir_given" = 'xno'],
+  [AS_IF([test x"$bindir_to_libdir" != 'x'],
+    [ocaml_libdir="$bindir_to_libdir"
+    target_libdir_is_relative=true
+    AS_CASE([$cygwin_build_env,$host],
+      [true,*-w64-mingw32*|true,*-pc-windows],
+        [build_bindir_to_libdir="$(LC_ALL=C.UTF-8 cygpath \
+                                   "$bindir_to_libdir")"],
+      [build_bindir_to_libdir="$bindir_to_libdir"])
+    AS_CASE([$build_bindir_to_libdir],
+      [./*],[libdir="$bindir${build_bindir_to_libdir[#].}"],
+      [../*],[libdir="$bindir/$build_bindir_to_libdir"],
+      [AC_MSG_ERROR(m4_normalize([--with-relative-libdir requires an explicit
+        relative path]))])])],
+  [AS_IF([test x"$bindir_to_libdir" != 'x'],
+    [AC_MSG_ERROR(m4_normalize([--with-relative-libdir and --libdir cannot both
+      be specified]))])])
 
 # Define a few macros that were defined in config/m-nt.h
 # but whose value is not guessed properly by configure
@@ -2691,6 +2895,79 @@ AS_CASE([$host],
     # as "Infinity" and "Inf" instead of the expected "inf"
     [AC_DEFINE([HAS_BROKEN_PRINTF], [1])])
 
+# Determine the three Runtime IDs (see runtime/Mangling.md)
+m4_define([ALPHABET], [0123456789abcdefghijklmnopqrstuv])
+AC_DEFUN([BASE32], ["$(echo 'ALPHABET' | cut -c $(expr \( $1 \) + 1))"])
+
+m4_cond(OCAML__DEVELOPMENT_VERSION, [true],
+  [m4_define([ID_VERSION], m4_eval((OCAML__RELEASE_NUMBER << 1) + 1))],
+  [m4_define([ID_VERSION], m4_eval((OCAML__RELEASE_NUMBER << 1)))])
+
+# Bits 0-4 (dev + low 4 bits of release)
+m4_define([QUINTET0],
+  [m4_substr(ALPHABET, m4_eval(ID_VERSION & 31), [1])])
+
+# Bits 5-6 (high 2 bits of release)
+m4_define([QUINTET1_ZINC],
+  [m4_substr(ALPHABET, m4_eval(ID_VERSION >> 5), [1])])
+
+# Bits 7-9 (low 3 bits of reserved)
+quintet1="QUINTET1_ZINC + $(expr \( $reserved_header_bits \* 4 \) % 32)"
+quintet1=BASE32([$quintet1])
+
+# Bits 10-11 (high 2 bits of reserved)
+quintet2_byte=BASE32([$reserved_header_bits / 8])
+
+# Bit 12 (no-flat-float-array)
+AS_IF([$flat_float_array],
+  [quintet2_zinc='0'],
+  [quintet2_byte="4 + $quintet2_byte"
+  quintet2_zinc='4'])
+# Bit 13 (fp)
+AS_IF([$frame_pointers],
+  [quintet2_native="8 + $quintet2_byte"],
+  [quintet2_native="$quintet2_byte"])
+# Bit 14 (tsan)
+AS_IF([$tsan],
+  [quintet2_native="16 + $quintet2_native"])
+
+quintet2_zinc=BASE32([$quintet2_zinc])
+quintet2_byte=BASE32([$quintet2_byte])
+quintet2_native=BASE32([$quintet2_native])
+
+# Bit 15 (int31)
+AS_IF([$arch64],
+  [quintet3_zinc='0'],
+  [quintet3_zinc='1'])
+# Bit 16 (static)
+AS_IF([! $supports_shared_libraries],
+  [quintet3_zinc="2 + $quintet3_zinc"])
+# Bit 17 (no-compression)
+AS_IF([test x"$zstd_status" != 'xok'],
+  [quintet3_zinc="4 + $quintet3_zinc"])
+# Bit 18 (ansi)
+AS_CASE([$target,$windows_unicode],
+  [*-*-mingw32,0|*-pc-windows,0],
+    [quintet3="8 + $quintet3_zinc"],
+  [quintet3="$quintet3_zinc"])
+# Bit 19 (mutable-string) cannot be set since OCaml 5.0
+
+quintet3_zinc=BASE32([$quintet3_zinc])
+quintet3=BASE32([$quintet3])
+
+zinc_runtime_id="QUINTET0[]QUINTET1_ZINC${quintet2_zinc}${quintet3_zinc}"
+bytecode_runtime_id="QUINTET0${quintet1}${quintet2_byte}${quintet3}"
+native_runtime_id="QUINTET0${quintet1}${quintet2_native}${quintet3}"
+
+# Update the values for is_official_release and release_number in
+# utils/config.common.ml.in (this is done when tools/autogen is run, not each
+# time configure is run!)
+m4_syscmd([sed -e '/^let is_official_release =/s/=.*/= ]'\
+'m4_if(OCAML__DEVELOPMENT_VERSION,true,false,true)[/' \
+    -e '/^let release_number =/s/=.*/= ]OCAML__RELEASE_NUMBER[/' \
+    utils/config.common.ml.in > utils/config.common.ml.in.new
+mv -f utils/config.common.ml.in.new utils/config.common.ml.in])
+
 # Do not permanently cache the result of flexdll.h
 unset ac_cv_header_flexdll_h
 
@@ -2699,17 +2976,52 @@ unset ac_cv_header_flexdll_h
 AC_CONFIG_COMMANDS_PRE([
   saved_exec_prefix="$exec_prefix"
   saved_prefix="$prefix"
+  prefix="$ocaml_prefix"
   AS_IF([test "x$prefix" = "xNONE"],[prefix="$ac_default_prefix"])
   AS_IF([test "x$exec_prefix" = "xNONE"],[exec_prefix="$prefix"])
   eval "exec_prefix=\"$exec_prefix\""
-  eval "ocaml_bindir=\"$bindir\""
-  eval "ocaml_libdir=\"$libdir\""
-  AS_IF([test x"$target_bindir" = 'x'],[target_bindir="$ocaml_bindir"])
-  AS_IF([test x"$target_launch_method" = 'x'],
-    [target_launch_method="$launch_method"])
+  # Set variables necessary to create utils/config.generated.ml.
+  # $HOST_BINDIR is always the absolute path to the binary directory, in host
+  #   format (i.e. potentially with backslashes on Windows).
+  # $TARGET_BINDIR can be specified by the caller when building cross-compilers,
+  #   and the value then is used unaltered. Otherwise, $TARGET_BINDIR is set to
+  #   '.' when the compiler is configured with --with-relative-libdir or the
+  #   value of $HOST_BINDIR otherwise.
+  # $ocaml_bindir is used in utils/config.generated.ml and is _empty_ if the
+  #   compiler is configured with --with-relative-libdir (otherwise the path
+  #   would be embedded in config.cmo)
+  eval "HOST_BINDIR=\"$ocaml_bindir\""
+  AS_IF([test "x$bindir_to_libdir" = 'x'],
+    [ocaml_bindir="$HOST_BINDIR"],
+    [ocaml_bindir=''])
+  AS_IF([test x"$TARGET_BINDIR" = 'x'],
+    [AS_IF([test "x$bindir_to_libdir" = 'x'],
+      [TARGET_BINDIR="$HOST_BINDIR"],
+      [TARGET_BINDIR='.'])])
+  eval "ocaml_libdir=\"$ocaml_libdir\""
+  AS_IF([test "x$bindir_to_libdir" = 'x'],
+    [TARGET_LIBDIR="$ocaml_libdir"],
+    [TARGET_LIBDIR="$bindir_to_libdir"])
+  AS_IF([test x"$launch_method_target" = 'x'],
+    [launch_method_target="$launch_method"])
   prefix="$saved_prefix"
   exec_prefix="$saved_exec_prefix"])
 
+# Create ld.conf
+AC_CONFIG_COMMANDS([runtime/ld.conf],
+  [rm -f runtime/ld.conf
+  test x"$ocaml_additional_stublibs_dir" = 'x' || \
+    echo "$ocaml_additional_stublibs_dir" > runtime/ld.conf
+  if $supports_shared_libraries; then
+    echo ".${default_separator}stublibs" >> runtime/ld.conf
+  fi
+  echo "." >> runtime/ld.conf],
+  [ocaml_additional_stublibs_dir=\
+'$(echo "$ocaml_additional_stublibs_dir" | sed -e "s/'/'\"'\"'/g")'
+  ocaml_libdir='$(echo "$ocaml_libdir" | sed -e "s/'/'\"'\"'/g")'
+  default_separator='$default_separator'
+  supports_shared_libraries='$supports_shared_libraries'])
+
 # Just before config.status is generated, determine the final values for MKEXE,
 # MKDLL, MKMAINDLL and MKEXE_VIA_CC. The final variables controlling these are:
 # $mkexe - the linking command and munged CFLAGS + any extra flexlink flags
diff --git a/driver/compenv.ml b/driver/compenv.ml
index d61d2b19fd0f..73f24bd605eb 100644
--- a/driver/compenv.ml
+++ b/driver/compenv.ml
@@ -594,7 +594,7 @@ type deferred_action =
   | ProcessCFile of string
   | ProcessOtherFile of string
   | ProcessObjects of string list
-  | ProcessDLLs of string list
+  | ProcessDLLs of bool * string list
 
 let c_object_of_filename name =
   Filename.chop_suffix (Filename.basename name) ".c" ^ Config.ext_obj
@@ -627,8 +627,8 @@ let process_action
       ccobjs := obj_name :: !ccobjs
   | ProcessObjects names ->
       ccobjs := names @ !ccobjs
-  | ProcessDLLs names ->
-      dllibs := names @ !dllibs
+  | ProcessDLLs (suffixed, names) ->
+      dllibs := (List.map (fun n -> (suffixed, n)) names) @ !dllibs
   | ProcessOtherFile name ->
       if Filename.check_suffix name ocaml_mod_ext
       || Filename.check_suffix name ocaml_lib_ext then
@@ -641,7 +641,7 @@ let process_action
         ccobjs := name :: !ccobjs
       end
       else if not !native_code && Filename.check_suffix name Config.ext_dll then
-        dllibs := name :: !dllibs
+        dllibs := (false, name) :: !dllibs
       else
         match Compiler_pass.of_input_filename name with
         | Some start_from ->
diff --git a/driver/compenv.mli b/driver/compenv.mli
index a5958554e76e..7260eb8affb5 100644
--- a/driver/compenv.mli
+++ b/driver/compenv.mli
@@ -52,7 +52,7 @@ type deferred_action =
   | ProcessCFile of string
   | ProcessOtherFile of string
   | ProcessObjects of string list
-  | ProcessDLLs of string list
+  | ProcessDLLs of bool * string list
 
 val c_object_of_filename : string -> string
 
diff --git a/driver/main_args.ml b/driver/main_args.ml
index ea07d15cf19f..7543eb874bea 100644
--- a/driver/main_args.ml
+++ b/driver/main_args.ml
@@ -89,6 +89,11 @@ let mk_custom f =
 let mk_dllib f =
   "-dllib", Arg.String f, "<lib>  Use the dynamically-loaded library <lib>"
 
+let mk_dllib_suffixed f =
+  "-dllib-suffixed", Arg.String f,
+  "<lib>  Use the dynamically-loaded library <lib>, with the runtime suffix \
+          appended to the name"
+
 let mk_dllpath f =
   "-dllpath", Arg.String f,
   "<dir>  Add <dir> to the run-time search path for shared libraries"
@@ -160,6 +165,10 @@ let mk_H f =
   "<dir>  Add <dir> to the list of \"hidden\" include directories\n\
  \     (Like -I, but the program can not directly reference these dependencies)"
 
+let mk_set_runtime_default f =
+  "-set-runtime-default", Arg.String f, "<param>=<value>  Set the default for \
+      runtime parameter <param> to <value> (see the manual for further details)"
+
 let mk_impl f =
   "-impl", Arg.String f, "<file>  Compile <file> as a .ml file"
 
@@ -517,6 +526,25 @@ let mk_unsafe_string =
  in
  "-unsafe-string", Arg.Unit err, " (option not available)"
 
+let mk_launch_method f =
+  "-launch-method", Arg.String f,
+  "<method>  Specify the mechanism for the bytecode launcher:\n\
+  \          exe - use the executable launcher in runtime-launch-info\n\
+  \          sh - use a #!, using sh if the interpreter path cannot be used\n\
+  \          /path/interpreter - use #!, or the given sh-compatible \n\
+  \            interpreter if the interpreter path cannot be used"
+
+let mk_search_method f =
+  "-runtime-search", Arg.Symbol (["disable"; "fallback"; "enable"], f),
+  Printf.sprintf
+    "  Control the way the bytecode header searches for the interpreter\n\
+    \    The following settings are supported:\n\
+    \      disable  use a fixed absolute path to the interpreter\n\
+    \      fallback search for interpreter only if not found at the absolute \
+                    path\n\
+    \      enable   always search for the interpreter\n\
+    \    The default setting is 'disable'."
+
 let mk_use_runtime f =
   "-use-runtime", Arg.String f,
   "<file>  Generate bytecode for the given runtime system"
@@ -872,6 +900,7 @@ module type Compiler_options = sig
   val _runtime_variant : string -> unit
   val _with_runtime : unit -> unit
   val _without_runtime : unit -> unit
+  val _set_runtime_default : string -> unit
   val _short_paths : unit -> unit
   val _thread : unit -> unit
   val _v : unit -> unit
@@ -912,10 +941,13 @@ module type Bytecomp_options = sig
   val _custom : unit -> unit
   val _no_check_prims : unit -> unit
   val _dllib : string -> unit
+  val _dllib_suffixed : string -> unit
   val _dllpath : string -> unit
   val _make_runtime : unit -> unit
   val _vmthread : unit -> unit
   val _use_runtime : string -> unit
+  val _launch_method : string -> unit
+  val _search_method : string -> unit
   val _output_complete_exe : unit -> unit
 
   val _dinstr : unit -> unit
@@ -1046,6 +1078,7 @@ struct
     mk_config_var F._config_var;
     mk_custom F._custom;
     mk_dllib F._dllib;
+    mk_dllib_suffixed F._dllib_suffixed;
     mk_dllpath F._dllpath;
     mk_dtypes F._annot;
     mk_for_pack_byt F._for_pack;
@@ -1099,6 +1132,7 @@ struct
     mk_without_runtime F._without_runtime;
     mk_safe_string;
     mk_safer_matching F._safer_matching;
+    mk_set_runtime_default F._set_runtime_default;
     mk_short_paths F._short_paths;
     mk_strict_sequence F._strict_sequence;
     mk_no_strict_sequence F._no_strict_sequence;
@@ -1111,6 +1145,8 @@ struct
     mk_unsafe_string;
     mk_use_runtime F._use_runtime;
     mk_use_runtime_2 F._use_runtime;
+    mk_launch_method F._launch_method;
+    mk_search_method F._search_method;
     mk_v F._v;
     mk_verbose F._verbose;
     mk_version F._version;
@@ -1314,6 +1350,7 @@ struct
     mk_S F._S;
     mk_safe_string;
     mk_safer_matching F._safer_matching;
+    mk_set_runtime_default F._set_runtime_default;
     mk_shared F._shared;
     mk_short_paths F._short_paths;
     mk_strict_sequence F._strict_sequence;
@@ -1756,6 +1793,19 @@ module Default = struct
     let _verbose = set verbose
   end
 
+  let fatalf fmt = Printf.ksprintf Compenv.fatal fmt
+
+  let parse_runtime_parameter opt =
+    let k, setting =
+      try Misc.cut_at opt '='
+      with Not_found ->
+        fatalf "-set-runtime-default: invalid runtime parameter '%s'. \
+                Expected <name>=<value>." opt in
+      if k = "standard_library_default" then
+        Clflags.standard_library_default := Some setting
+      else
+        fatalf "-set-runtime-default: unrecognized runtime parameter %s." k
+
   module Compiler = struct
     let _a = set make_archive
     let _annot = set annotations
@@ -1794,6 +1844,7 @@ module Default = struct
     let _plugin _p = plugin := true
     let _pp s = preprocessor := (Some s)
     let _runtime_variant s = runtime_variant := s
+    let _set_runtime_default s = parse_runtime_parameter s
     let _stop_after pass =
       let module P = Compiler_pass in
         match P.of_string pass with
@@ -1923,7 +1974,9 @@ third-party libraries such as Lwt, but with a different API."
     let _custom = set custom_runtime
     let _dcamlprimc = set keep_camlprimc_file
     let _dinstr = set dump_instr
-    let _dllib s = Compenv.defer (ProcessDLLs (Misc.rev_split_words s))
+    let _dllib s = Compenv.defer (ProcessDLLs (false, Misc.rev_split_words s))
+    let _dllib_suffixed s =
+      Compenv.defer (ProcessDLLs (true, Misc.rev_split_words s))
     let _dllpath s = dllpaths := ((!dllpaths) @ [s])
     let _make_runtime () =
       custom_runtime := true; make_runtime := true; link_everything := true
@@ -1937,6 +1990,34 @@ third-party libraries such as Lwt, but with a different API."
     let _output_obj () = output_c_object := true; custom_runtime := true
     let _use_prims s = use_prims := s
     let _use_runtime s = use_runtime := s
+    let _launch_method s =
+      let setting =
+        try
+          let s, bindir = Misc.cut_at s ' ' in
+          target_bindir := bindir;
+          s
+        with Not_found ->
+          s
+      in
+      match setting with
+      | "exe" ->
+          launch_method := Config.Executable;
+      | "sh" ->
+          launch_method := Config.Shebang None
+      | s when s <> "" && s.[0] = '/' ->
+          launch_method := Config.Shebang (Some s)
+      | _ ->
+          Compenv.fatal
+            "-launch-method: expect sh, exe or an absolute path for <method>"
+    let _search_method = function
+    | "disable" ->
+        search_method := Config.Disable
+    | "fallback" ->
+        search_method := Config.Fallback
+    | "enable" ->
+        search_method := Config.Enable
+    | _ ->
+        assert false
     let _v () = Compenv.print_version_and_library "compiler"
     let _vmthread () = Compenv.fatal vmthread_removed_message
   end
diff --git a/driver/main_args.mli b/driver/main_args.mli
index 554b1fa36bad..14a69c6f45cc 100644
--- a/driver/main_args.mli
+++ b/driver/main_args.mli
@@ -113,6 +113,7 @@ module type Compiler_options = sig
   val _runtime_variant : string -> unit
   val _with_runtime : unit -> unit
   val _without_runtime : unit -> unit
+  val _set_runtime_default : string -> unit
   val _short_paths : unit -> unit
   val _thread : unit -> unit
   val _v : unit -> unit
@@ -154,10 +155,13 @@ module type Bytecomp_options = sig
   val _custom : unit -> unit
   val _no_check_prims : unit -> unit
   val _dllib : string -> unit
+  val _dllib_suffixed : string -> unit
   val _dllpath : string -> unit
   val _make_runtime : unit -> unit
   val _vmthread : unit -> unit
   val _use_runtime : string -> unit
+  val _launch_method : string -> unit
+  val _search_method : string -> unit
   val _output_complete_exe : unit -> unit
 
   val _dinstr : unit -> unit
diff --git a/lambda/lambda.ml b/lambda/lambda.ml
index 9fdbc8146e9f..20074a1828f3 100644
--- a/lambda/lambda.ml
+++ b/lambda/lambda.ml
@@ -25,6 +25,7 @@ type compile_time_constant =
   | Ostype_win32
   | Ostype_cygwin
   | Backend_type
+  | Standard_library_default
 
 type immediate_or_pointer =
   | Immediate
diff --git a/lambda/lambda.mli b/lambda/lambda.mli
index 6f5d9717914b..eb72cf09eaff 100644
--- a/lambda/lambda.mli
+++ b/lambda/lambda.mli
@@ -26,6 +26,7 @@ type compile_time_constant =
   | Ostype_win32
   | Ostype_cygwin
   | Backend_type
+  | Standard_library_default
 
 type immediate_or_pointer =
   | Immediate
diff --git a/lambda/printlambda.ml b/lambda/printlambda.ml
index 76989a4035f7..c5153580e1ce 100644
--- a/lambda/printlambda.ml
+++ b/lambda/printlambda.ml
@@ -266,7 +266,8 @@ let primitive ppf = function
        | Ostype_unix -> "ostype_unix"
        | Ostype_win32 -> "ostype_win32"
        | Ostype_cygwin -> "ostype_cygwin"
-       | Backend_type -> "backend_type" in
+       | Backend_type -> "backend_type"
+       | Standard_library_default -> "standard_library_default" in
      fprintf ppf "sys.constant_%s" const_name
   | Pisint -> fprintf ppf "isint"
   | Pisout -> fprintf ppf "isout"
diff --git a/lambda/translprim.ml b/lambda/translprim.ml
index df46ea3a44af..ca50c898a0a8 100644
--- a/lambda/translprim.ml
+++ b/lambda/translprim.ml
@@ -148,6 +148,8 @@ let primitives_table =
     "%ostype_unix", Primitive ((Pctconst Ostype_unix), 1);
     "%ostype_win32", Primitive ((Pctconst Ostype_win32), 1);
     "%ostype_cygwin", Primitive ((Pctconst Ostype_cygwin), 1);
+    "%standard_library_default",
+    Primitive ((Pctconst Standard_library_default), 1);
     "%frame_pointers", Frame_pointers;
     "%negint", Primitive (Pnegint, 1);
     "%succint", Primitive ((Poffsetint 1), 1);
diff --git a/man/Makefile b/man/Makefile
index 10cc8bbe417b..e43a3451bc66 100644
--- a/man/Makefile
+++ b/man/Makefile
@@ -14,6 +14,7 @@
 #**************************************************************************
 
 ROOTDIR = ..
+SUBDIR_NAME = man
 include $(ROOTDIR)/Makefile.common
 
 MANPAGES = $(addsuffix .1,\
@@ -22,5 +23,4 @@ MANPAGES = $(addsuffix .1,\
 
 .PHONY: install
 install:
-	$(MKDIR) '$(INSTALL_PROGRAMS_MAN_DIR)'
-	$(INSTALL_DATA) $(MANPAGES) '$(INSTALL_PROGRAMS_MAN_DIR)'
+	$(call INSTALL_ITEMS, $(MANPAGES), man, $(INSTALL_MANDIR_PROGRAMS))
diff --git a/man/ocamlc.1 b/man/ocamlc.1
index f503e948c79b..005a2fe52cad 100644
--- a/man/ocamlc.1
+++ b/man/ocamlc.1
@@ -355,6 +355,15 @@ to be loaded dynamically by the run-time system
 .BR ocamlrun (1)
 at program start-up time.
 .TP
+.BI \-dllib\-suffixed\ \-l libname
+As for
+.BI \-dllib
+but the name recorded is mangled by
+.BR ocamlrun (1)
+at program start-up time. This is used for C stub libraries; see
+.B ocamlmklib\ \-suffixed
+for further information.
+.TP
 .BI \-dllpath " dir"
 Adds the directory
 .I dir
@@ -474,6 +483,24 @@ source code.
 Labels are not ignored in types, labels may be used in applications,
 and labelled parameters can be given in any order.  This is the default.
 .TP
+.BI \-launch\-method " method"
+Specifies the mechanism used by normal bytecode executables to find the
+interpreter.
+The following methods are supported:
+
+.B exe
+A small executable stub launcher contained in the runtime-launch-info file is
+prepended to the bytecode image.
+
+.B sh
+A #! header is used. If the full path to the required interpreter is not
+suitable for a #! line, a small shell script is generated instead, using the sh
+interpreter found in PATH.
+
+.B /path/interpreter
+As for sh, but if the interpreter cannot be used in #! line then
+/path/intepreter is used instead of searching for sh in PATH.
+.TP
 .B \-linkall
 Force all modules contained in libraries to be linked in. If this
 flag is not given, unreferenced modules are not linked in. When
@@ -653,6 +680,25 @@ flag, you must use it again for all dependencies.
 Do no allow arbitrary recursive types during type-checking.
 This is the default.
 .TP
+.BI \-runtime\-search " method"
+Controls whether the header used by normal bytecode executables is permitted to
+search for the interpreter, or requires it to be at a fixed location.
+The following methods are supported:
+
+.B disable
+A fixed absolute path to the interpreter is used, and the executable will not
+launch if the interpreter is not found at this location.
+
+.B fallback
+A fixed absolute path to the interpreter is used, but if the executable cannot
+find the interpreter at this location then it will search first in the directory
+containing the executable and then in PATH.
+
+.B enable
+The executable searches for the interpreter first in the directory containing
+the executable and then in PATH. No absolute path to the interpreter is
+recorded.
+.TP
 .BI \-runtime\-variant " suffix"
 Add
 .I suffix
@@ -674,6 +720,15 @@ This allows to detect match failures even if a pattern-matching was
 wrongly assumed to be exhaustive. This only impacts GADT and
 polymorphic variant compilation.
 .TP
+.BI \-set\-runtime\-default " setting=value"
+When linking an executable, override the default value for a runtime setting.
+The only currently supported setting is:
+
+.B standard_library_default
+Specifies the default location used by the executable to locate the Standard
+Library. By default, this is the absolute path to the Standard Library the
+compiler itself was configured with.
+.TP
 .B \-short\-paths
 When a type is visible under several module-paths, use the shortest
 one when printing the type's name in inferred interfaces and error and
diff --git a/man/ocamlopt.1 b/man/ocamlopt.1
index 52bed675ef2a..9b84757a95bf 100644
--- a/man/ocamlopt.1
+++ b/man/ocamlopt.1
@@ -593,6 +593,15 @@ Save intermediate representation after the given compilation pass. The currently
 supported passes are:
 .BR scheduling .
 .TP
+.BI \-set\-runtime\-default " setting=value"
+When linking an executable, override the default value for a runtime setting.
+The only currently supported setting is:
+
+.B standard_library_default
+Specifies the default location used by the executable to locate the Standard
+Library. By default, this is the absolute path to the Standard Library the
+compiler itself was configured with.
+.TP
 .B \-shared
 Build a plugin (usually .cmxs) that can be dynamically loaded with
 the
diff --git a/manual/src/cmds/runtime.etex b/manual/src/cmds/runtime.etex
index 5f41a2d097b9..ac7e827d2186 100644
--- a/manual/src/cmds/runtime.etex
+++ b/manual/src/cmds/runtime.etex
@@ -250,7 +250,9 @@ library directory.  Users can add there the names of other directories
 containing frequently-used shared libraries; however, for consistency
 of installation, we recommend that shared libraries are installed
 directly in the system "stublibs" directory, rather than adding lines
-to the "ld.conf" file.
+to the "ld.conf" file. "ocamlrun" will add lines from "ld.conf" files
+found in the directories pointed to by "OCAMLLIB", "CAMLLIB" and the
+standard library directory, in that order.
 \item Default directories searched by the system dynamic loader.
 Under Unix, these generally include "/lib" and "/usr/lib", plus the
 directories listed in the file "/etc/ld.so.conf" and the environment
diff --git a/manual/src/cmds/unified-options.etex b/manual/src/cmds/unified-options.etex
index 96cc29ce3323..08d2fd3a70f7 100644
--- a/manual/src/cmds/unified-options.etex
+++ b/manual/src/cmds/unified-options.etex
@@ -229,6 +229,14 @@ Arrange for the C shared library "dll"\var{libname}".so"
 by the run-time system "ocamlrun" at program start-up time.
 }%comp
 
+\comp{
+\item["-dllib-suffixed" "-l"\var{libname}]
+As for "-dllib" but the name recorded is mangled with the Runtime ID and host of
+the interpreter before being loaded by the run-time system "ocamlrun" at program
+start-up time. Ths is used for C stub libraries, for example by DLLs produced
+with "ocamlmklib -suffixed".
+}%comp
+
 \comp{\item["-dllpath" \var{dir}]
 Adds the directory \var{dir} to the run-time search path for shared
 C libraries.  At link-time, shared libraries are searched in the
@@ -381,6 +389,23 @@ source code.
 Labels are not ignored in types, labels may be used in applications,
 and labelled parameters can be given in any order.  This is the default.
 
+\comp{%
+\item["-launch-method" \var{method}]
+Specifies the mechanism used by normal bytecode executables to find the
+interpreter.
+The following methods are supported:
+\begin{description}
+  \item["exe"] A small executable stub launcher contained in the
+    runtime-launch-info file is prepended to the bytecode image.
+  \item["sh"] A "#!" header is used. If the full path to the required
+    interpreter is not suitable for a "#!" line, a small shell script is
+    generated instead, using the "sh" interpreter found in "PATH".
+  \item["/path/interpreter"] As for "sh", but if the interpreter cannot be used
+    in "#!" line then "/path/intepreter" is used instead of searching for "sh"
+    in "PATH".
+\end{description}
+}%comp
+
 \notop{%
 \item["-linkall"]
 Force all modules contained in libraries to be linked in. If this
@@ -663,6 +688,23 @@ only recursive types where the recursion goes through an object type
 are supported. \notop{Note that once you have created an interface using this
 flag, you must use it again for all dependencies.}
 
+\comp{%
+\item["-runtime-search" \var{method}]
+Controls whether the header used by normal bytecode executables is permitted to
+search for the interpreter, or requires it to be at a fixed location.
+The following methods are supported:
+\begin{description}
+  \item["disable"] A fixed absolute path to the interpreter is used, and the
+  executable will not launch if the interpreter is not found at this location.
+  \item["fallback"] A fixed absolute path to the interpreter is used, but if the
+  executable cannot find the interpreter at this location then it will search
+  first in the directory containing the executable and then in "PATH".
+  \item["enable"] The executable searches for the interpreter first in the
+  directory containing the executable and then in "PATH". No absolute path to
+  the interpreter is recorded.
+\end{description}
+}%comp
+
 \notop{%
 \item["-runtime-variant" \var{suffix}]
 Add the \var{suffix} string to the name of the runtime library used by
@@ -706,6 +748,17 @@ using "compiler-libs" library (see
 ).
 }%nat
 
+\notop{%
+\item["-set-runtime-default" \var{name=value}]
+When linking an executable, override the default value for a runtime setting.
+The currently supported settings are:
+\begin{description}
+  \item["standard_library_default"] Specifies the default location used by the
+    executable to locate the Standard Library. By default, this is the absolute
+    path to the Standard Library the compiler itself was configured with.
+\end{description}
+}%notop
+
 \nat{%
 \item["-shared"]
 Build a plugin (usually ".cmxs") that can be dynamically loaded with
diff --git a/middle_end/closure/closure.ml b/middle_end/closure/closure.ml
index 880773fbac09..26e380767573 100644
--- a/middle_end/closure/closure.ml
+++ b/middle_end/closure/closure.ml
@@ -1051,22 +1051,29 @@ let rec close ({ backend; fenv; cenv ; mutable_vars } as env) lam =
               None ubody),
        approx)
   (* Compile-time constants *)
-  | Lprim(Pctconst c, [arg], _loc) ->
-      let cst, approx =
-        match c with
-        | Big_endian -> make_const_bool B.big_endian
-        | Word_size -> make_const_int (8*B.size_int)
-        | Int_size -> make_const_int (8*B.size_int - 1)
-        | Max_wosize -> make_const_int ((1 lsl ((8*B.size_int) - 10)) - 1 )
-        | Ostype_unix -> make_const_bool (Sys.os_type = "Unix")
-        | Ostype_win32 -> make_const_bool (Sys.os_type = "Win32")
-        | Ostype_cygwin -> make_const_bool (Sys.os_type = "Cygwin")
-        | Backend_type ->
-            make_const_int 0 (* tag 0 is the same as Native here *)
+  | Lprim(Pctconst c, [arg], loc) ->
+      let cst f v =
+        let cst, approx = f v in
+        let arg, _approx = close env arg in
+        let id = Ident.create_local "dummy" in
+        Ulet(Immutable, Pgenval, VP.create id, arg, cst), approx
       in
-      let arg, _approx = close env arg in
-      let id = Ident.create_local "dummy" in
-      Ulet(Immutable, Pgenval, VP.create id, arg, cst), approx
+      begin match c with
+      | Big_endian -> cst make_const_bool B.big_endian
+      | Word_size -> cst make_const_int (8*B.size_int)
+      | Int_size -> cst make_const_int (8*B.size_int - 1)
+      | Max_wosize -> cst make_const_int ((1 lsl ((8*B.size_int) - 10)) - 1)
+      | Ostype_unix -> cst make_const_bool (Sys.os_type = "Unix")
+      | Ostype_win32 -> cst make_const_bool (Sys.os_type = "Win32")
+      | Ostype_cygwin -> cst make_const_bool (Sys.os_type = "Cygwin")
+      | Backend_type ->
+          cst make_const_int 0 (* tag 0 is the same as Native here *)
+      | Standard_library_default ->
+          Compilenv.need_stdlib_location ();
+          let dbg = Debuginfo.from_location loc in
+          let id = Ident.name Compilenv.stdlib_symbol_name in
+          Uprim(P.Pread_symbol id, [], dbg), Value_const (Uconst_ref (id, None))
+      end
   | Lprim(Pignore, [arg], _loc) ->
       let expr, approx = make_const_int 0 in
       Usequence(fst (close env arg), expr), approx
@@ -1458,7 +1465,9 @@ let collect_exported_structured_constants a =
     | Uconst_ref (s, (Some c)) ->
         Compilenv.add_exported_constant s;
         structured_constant c
-    | Uconst_ref (_s, None) -> assert false (* Cannot be generated *)
+    | Uconst_ref (s, None) ->
+        (* Only generated in one context *)
+        assert (s = Ident.name Compilenv.stdlib_symbol_name)
     | Uconst_int _ -> ()
   and structured_constant = function
     | Uconst_block (_, ul) -> List.iter const ul
diff --git a/middle_end/compilenv.ml b/middle_end/compilenv.ml
index d975c1781ce6..b7287aa67e96 100644
--- a/middle_end/compilenv.ml
+++ b/middle_end/compilenv.ml
@@ -89,6 +89,7 @@ let current_unit =
     ui_force_link = false;
     ui_export_info = default_ui_export_info;
     ui_for_pack = None }
+let current_ui_need_stdlib = ref false
 
 let symbol_separator =
   match Config.ccomp_type with
@@ -128,6 +129,7 @@ let reset ?packname name =
   current_unit.ui_send_fun <- [];
   current_unit.ui_force_link <- !Clflags.link_everything;
   current_unit.ui_for_pack <- packname;
+  current_ui_need_stdlib := false;
   Hashtbl.clear exported_constants;
   structured_constants := structured_constants_empty;
   current_unit.ui_export_info <- default_ui_export_info;
@@ -258,11 +260,16 @@ let global_approx id =
       | None -> Clambda.Value_unknown
       | Some ui -> get_clambda_approx ui
 
+(* The name of the symbol defined globally for %standard_library_default *)
+let stdlib_symbol_name = Ident.create_persistent "caml_standard_library_nat"
+
 (* Return the symbol used to refer to a global identifier *)
 
 let symbol_for_global id =
   if Ident.is_predef id then
     "caml_exn_" ^ Ident.name id
+  else if Ident.same stdlib_symbol_name id then
+    Ident.name id
   else begin
     let unitname = Ident.name id in
     match
@@ -290,7 +297,7 @@ let is_predefined_exception sym =
 
 let symbol_for_global' id =
   let sym_label = Linkage_name.create (symbol_for_global id) in
-  if Ident.is_predef id then
+  if Ident.is_predef id || Ident.same stdlib_symbol_name id then
     Symbol.of_global_linkage predefined_exception_compilation_unit sym_label
   else
     Symbol.of_global_linkage (unit_for_global id) sym_label
@@ -348,11 +355,42 @@ let need_send_fun n =
   if not (List.mem n current_unit.ui_send_fun) then
     current_unit.ui_send_fun <- n :: current_unit.ui_send_fun
 
+(* Record that caml_standard_library_nat is needed *)
+
+let need_stdlib_location () =
+  current_ui_need_stdlib := true
+
+(* Relocatable OCaml needs an extra piece of information recorded in cmx format,
+   but for backporting to previous releases it was desirable not to change the
+   magic numbers. The additional ui_need_stdlib field is stored, but not
+   declared in the type, which allows .cmx files produced with earlier versions
+   of the compiler in the same series still to be loaded. *)
+let unit_info_size = Obj.size (Obj.repr current_unit)
+let needs_stdlib_location ui =
+  let ui = Obj.repr ui in
+  if Obj.size ui <= unit_info_size then
+    false
+  else
+    let field = Obj.field ui unit_info_size in
+    if Obj.is_int field then
+      (Obj.obj field : bool)
+    else
+      false
+
 (* Write the description of the current unit *)
 
-let write_unit_info info filename =
+let write_unit_info ?(ui_need_stdlib=false) info filename =
   let oc = open_out_bin filename in
   output_string oc cmx_magic_number;
+  let info =
+    let[@ocaml.warning "+missing-record-field-pattern"]
+      {ui_name; ui_symbol; ui_defines; ui_imports_cmi;
+       ui_imports_cmx; ui_curry_fun; ui_apply_fun; ui_send_fun;
+       ui_export_info; ui_force_link; ui_for_pack} = info in
+    ui_name, ui_symbol, ui_defines, ui_imports_cmi,
+    ui_imports_cmx, ui_curry_fun, ui_apply_fun, ui_send_fun,
+    ui_export_info, ui_force_link, ui_for_pack, ui_need_stdlib
+  in
   output_value oc info;
   flush oc;
   let crc = Digest.file filename in
@@ -361,7 +399,7 @@ let write_unit_info info filename =
 
 let save_unit_info filename =
   current_unit.ui_imports_cmi <- Env.imports();
-  write_unit_info current_unit filename
+  write_unit_info ~ui_need_stdlib:!current_ui_need_stdlib current_unit filename
 
 let current_unit () =
   match Compilation_unit.get_current () with
diff --git a/middle_end/compilenv.mli b/middle_end/compilenv.mli
index 2bcbca98b830..36d4adc3a0ef 100644
--- a/middle_end/compilenv.mli
+++ b/middle_end/compilenv.mli
@@ -104,6 +104,17 @@ val need_send_fun: int -> unit
         (* Record the need of a currying (resp. application,
            message sending) function with the given arity *)
 
+val need_stdlib_location: unit -> unit
+        (* Record that caml_standard_library_nat needs to be initialised if this
+           unit is linked. *)
+
+val needs_stdlib_location: unit_infos -> bool
+        (* Accessor for the hidden ui_need_stdlib field *)
+
+val stdlib_symbol_name: Ident.t
+        (* The name of the symbol defined globally for
+           %standard_library_default *)
+
 val new_const_symbol : unit -> string
 val closure_symbol : Closure_id.t -> Symbol.t
         (* Symbol of a function if the function is
@@ -135,7 +146,7 @@ val backtrack: structured_constants -> unit
 
 val read_unit_info: string -> unit_infos * Digest.t
         (* Read infos and MD5 from a [.cmx] file. *)
-val write_unit_info: unit_infos -> string -> unit
+val write_unit_info: ?ui_need_stdlib:bool -> unit_infos -> string -> unit
         (* Save the given infos in the given file *)
 val save_unit_info: string -> unit
         (* Save the infos for the current unit in the given file *)
diff --git a/middle_end/flambda/closure_conversion.ml b/middle_end/flambda/closure_conversion.ml
index 6b9e8d967019..4c68b6c11e35 100644
--- a/middle_end/flambda/closure_conversion.ml
+++ b/middle_end/flambda/closure_conversion.ml
@@ -390,23 +390,30 @@ let rec close t env (lam : Lambda.lambda) : Flambda.t =
         ~name:Names.raise)
   | Lprim (Pctconst c, [arg], _loc) ->
       let module Backend = (val t.backend) in
-      let const =
-        begin match c with
-        | Big_endian -> lambda_const_bool Backend.big_endian
-        | Word_size -> lambda_const_int (8*Backend.size_int)
-        | Int_size -> lambda_const_int (8*Backend.size_int - 1)
-        | Max_wosize ->
-            lambda_const_int ((1 lsl ((8*Backend.size_int) - 10)) - 1)
-        | Ostype_unix -> lambda_const_bool (String.equal Sys.os_type "Unix")
-        | Ostype_win32 -> lambda_const_bool (String.equal Sys.os_type "Win32")
-        | Ostype_cygwin -> lambda_const_bool (String.equal Sys.os_type "Cygwin")
-        | Backend_type ->
-            Lambda.const_int 0 (* tag 0 is the same as Native *)
-        end
-      in
-      close t env
-        (Lambda.Llet(Strict, Pgenval, Ident.create_local "dummy",
+      let cst f v =
+        let const = f v in
+        close t env (Lambda.Llet(Strict, Pgenval, Ident.create_local "dummy",
                      arg, Lconst const))
+      in
+      begin match c with
+      | Big_endian -> cst lambda_const_bool Backend.big_endian
+      | Word_size -> cst lambda_const_int (8*Backend.size_int)
+      | Int_size -> cst lambda_const_int (8*Backend.size_int - 1)
+      | Max_wosize ->
+          cst lambda_const_int ((1 lsl ((8*Backend.size_int) - 10)) - 1)
+      | Ostype_unix ->
+          cst lambda_const_bool (String.equal Sys.os_type "Unix")
+      | Ostype_win32 ->
+          cst lambda_const_bool (String.equal Sys.os_type "Win32")
+      | Ostype_cygwin ->
+          cst lambda_const_bool (String.equal Sys.os_type "Cygwin")
+      | Backend_type -> cst Lambda.const_int 0 (* tag 0 is the same as Native *)
+      | Standard_library_default ->
+          Compilenv.need_stdlib_location ();
+          let symbol = t.symbol_for_global' Compilenv.stdlib_symbol_name in
+          t.imported_symbols <- Symbol.Set.add symbol t.imported_symbols;
+          name_expr (Symbol symbol) ~name:Names.pgetglobal
+      end
   | Lprim (Pfield _, [Lprim (Pgetglobal id, [],_)], _)
       when Ident.same id t.current_unit_id ->
     Misc.fatal_errorf "[Pfield (Pgetglobal ...)] for the current compilation \
diff --git a/ocaml-variants.opam b/ocaml-variants.opam
index 6787e2bc41bf..e1c3079357c5 100644
--- a/ocaml-variants.opam
+++ b/ocaml-variants.opam
@@ -1,7 +1,7 @@
 opam-version: "2.0"
-version: "5.3.1+trunk"
+version: "5.3.1+relocatable"
 license: "LGPL-2.1-or-later WITH OCaml-LGPL-linking-exception"
-synopsis: "OCaml 5.3 development version"
+synopsis: "Relocatable OCaml 5.3 branch"
 maintainer: "caml-list@inria.fr"
 authors: [
   "Xavier Leroy"
@@ -9,6 +9,7 @@ authors: [
   "Alain Frisch"
   "Jacques Garrigue"
   "Didier Rémy"
+  "KC Sivaramakrishnan"
   "Jérôme Vouillon"
 ]
 homepage: "https://github.com/ocaml/ocaml/"
@@ -38,18 +39,18 @@ depends: [
   # facility is not yet available for other platforms.
   "host-arch-x86_32" {os != "win32" & arch = "x86_32" & post}
   ("host-arch-x86_64" {os != "win32" & arch = "x86_64" & post} |
-   ("host-arch-x86_32" {os != "win32" & arch = "x86_64" & post} & "ocaml-option-32bit" {os != "win32" & arch = "x86_64"}))
+   ("host-arch-x86_32" {os != "win32" & arch = "x86_64" & post} & "ocaml-option-32bit" {build & os != "win32" & arch = "x86_64"}))
   "host-arch-unknown" {os != "win32" & arch != "arm32" & arch != "arm64" & arch != "ppc64" & arch != "riscv64" & arch != "s390x" & arch != "x86_32" & arch != "x86_64" & post}
 
   # Port selection (Windows)
   # amd64 mingw-w64 / MSVC
-  (("arch-x86_64" {os = "win32" & arch = "x86_64"} &
-     (("system-mingw" & "mingw-w64-shims" {os-distribution = "cygwin" & build}) |
-      ("system-msvc" & "winpthreads" & "ocaml-option-no-compression" {os = "win32"}))) |
+  (("arch-x86_64" {build & os = "win32" & arch = "x86_64"} &
+     (("system-mingw" {build} & "mingw-w64-shims" {os-distribution = "cygwin" & build}) |
+      ("system-msvc" {build} & "winpthreads" {os = "win32"} & "ocaml-option-no-compression" {build & os = "win32"}))) |
   # i686 mingw-w64 / MSVC
-   ("arch-x86_32" {os = "win32"} & "ocaml-option-bytecode-only" {os = "win32"} &
-     (("system-mingw" & "mingw-w64-shims" {os-distribution = "cygwin" & build}) |
-      ("system-msvc" & "winpthreads" & "ocaml-option-no-compression" {os = "win32"}))) |
+   ("arch-x86_32" {build & os = "win32"} & "ocaml-option-bytecode-only" {build & os = "win32"} &
+     (("system-mingw" {build} & "mingw-w64-shims" {os-distribution = "cygwin" & build}) |
+      ("system-msvc" {build} & "winpthreads" {os = "win32"} & "ocaml-option-no-compression" {build & os = "win32"}))) |
   # Non-Windows systems
    "host-system-other" {os != "win32" & post})
 
@@ -75,8 +76,12 @@ build: [
     "--host=i686-w64-mingw32"   {os-distribution = "cygwin" & system-mingw:installed & arch-x86_32:installed}
     "--prefix=%{prefix}%"
     "--docdir=%{doc}%/ocaml"
+    "--with-additional-stublibsdir"
+    "--with-relative-libdir"
+    "--enable-runtime-search"
+    "--enable-runtime-search-target=fallback"
     "--with-flexdll=%{flexdll:share}%" {os = "win32" & flexdll:installed}
-    "--with-winpthreads-msvc=%{winpthreads:share}%" {system-msvc:installed}
+    "--with-winpthreads-msvc=%{winpthreads:share}%" {winpthreads:installed & system-msvc:installed}
     "-C"
     "--with-afl" {ocaml-option-afl:installed}
     "--disable-native-compiler" {ocaml-option-bytecode-only:installed}
@@ -102,8 +107,9 @@ build: [
     "--disable-warn-error"
   ]
   [make "-j%{jobs}%"]
+  [make "INSTALL_MODE=opam" "install"]
 ]
-install: [make "install"]
+install: ["sh" "./%{name}%-fixup.sh" prefix]
 depopts: [
   "ocaml-option-32bit"
   "ocaml-option-afl"
diff --git a/ocamltest/ocaml_actions.ml b/ocamltest/ocaml_actions.ml
index 4c261d93144f..30ef16c15d5a 100644
--- a/ocamltest/ocaml_actions.ml
+++ b/ocamltest/ocaml_actions.ml
@@ -629,7 +629,9 @@ let mklib log env =
     Ocaml_commands.ocamlrun_ocamlmklib;
     "-ocamlc '" ^ ocamlc_command ^ "'";
     "-o " ^ program
-  ] @ modules env in
+  ] @ (if Ocamltest_config.suffixing then ["-suffixed"] else [])
+    @ modules env
+  in
   let expected_exit_status = 0 in
   let exit_status =
     Actions_helpers.run_cmd
diff --git a/ocamltest/ocaml_tests.ml b/ocamltest/ocaml_tests.ml
index baf643ec33c9..75930567159d 100644
--- a/ocamltest/ocaml_tests.ml
+++ b/ocamltest/ocaml_tests.ml
@@ -46,7 +46,16 @@ let bytecode =
     check_program_output;
   ] @
   (if not Sys.win32 && Ocamltest_config.native_compiler then
-    opt_build @ [compare_bytecode_programs]
+    (* If the compiler is configured using --with-relative-libdir then at
+       present we can't compare the bytecode programs because ocamlc.opt and
+       ocamlrun are at different levels in the build tree, but they're both
+       configured with the same relative directory path.
+       This problem will disappear when ocamltest runs the testsuite against a
+       compiler in an install-tree like way. *)
+    if Ocamltest_config.has_relative_libdir then
+      opt_build
+    else
+      opt_build @ [compare_bytecode_programs]
   else
     []
   )
diff --git a/ocamltest/ocamltest_config.ml.in b/ocamltest/ocamltest_config.ml.in
index 2c53e45ce39f..03a3ca7b8052 100644
--- a/ocamltest/ocamltest_config.ml.in
+++ b/ocamltest/ocamltest_config.ml.in
@@ -95,3 +95,7 @@ let instrumented_runtime = @instrumented_runtime@
 let frame_pointers = @frame_pointers@
 
 let tsan = @tsan@
+
+let has_relative_libdir = @target_libdir_is_relative@
+
+let suffixing = @suffixing@
diff --git a/ocamltest/ocamltest_config.mli b/ocamltest/ocamltest_config.mli
index d75ae87fbe39..ec5f97abf468 100644
--- a/ocamltest/ocamltest_config.mli
+++ b/ocamltest/ocamltest_config.mli
@@ -133,3 +133,10 @@ val frame_pointers : bool
 
 val tsan : bool
 (** Whether ThreadSanitizer support has been enabled at configure time *)
+
+val has_relative_libdir : bool
+(** Whether the compiler has been configured using --with-relative-libdir *)
+
+val suffixing : bool
+(** Whether C stub library filenames are being mangled with the Bytecode
+    Runtime ID and {!Config.target}. *)
diff --git a/otherlibs/Makefile b/otherlibs/Makefile
index d76643bd297b..83dce3235d50 100644
--- a/otherlibs/Makefile
+++ b/otherlibs/Makefile
@@ -14,6 +14,7 @@
 #**************************************************************************
 
 ROOTDIR=..
+SUBDIR_NAME=otherlibs
 include $(ROOTDIR)/Makefile.common
 
 # Although the OTHERLIBS variable is defined in ../Makefile.config,
diff --git a/otherlibs/Makefile.otherlibs.common b/otherlibs/Makefile.otherlibs.common
index f08dd13ef8cc..d679b65f2db8 100644
--- a/otherlibs/Makefile.otherlibs.common
+++ b/otherlibs/Makefile.otherlibs.common
@@ -16,6 +16,7 @@
 # Common Makefile for otherlibs
 
 ROOTDIR=../..
+SUBDIR_NAME=otherlibs/$(LIBNAME)
 include $(ROOTDIR)/Makefile.common
 include $(ROOTDIR)/Makefile.best_binaries
 
@@ -35,6 +36,9 @@ ifeq "$(FLAMBDA)" "true"
 OPTCOMPFLAGS += -O3
 endif
 MKLIB=$(OCAMLRUN) $(ROOTDIR)/tools/ocamlmklib$(EXE)
+ifeq "$(SUFFIXING)" "true"
+MKLIB += -suffixed
+endif
 
 # Variables that must be defined by individual libraries:
 # LIBNAME
@@ -52,8 +56,13 @@ CAMLOBJS_NAT ?= $(CAMLOBJS:.cmo=.cmx)
 CLIBNAME ?= $(LIBNAME)
 
 ifeq "$(C_SOURCES)" ""
-STUBSLIB=
+
+STUBSLIB_BYTECODE=
+STUBSLIB_NATIVE=
+STUBSDLL=
+
 else
+
 COBJS_BYTECODE = $(C_SOURCES:.c=.b.$(O))
 COBJS_NATIVE = $(C_SOURCES:.c=.n.$(O))
 COBJS = $(COBJS_BYTECODE) $(COBJS_NATIVE)
@@ -62,6 +71,12 @@ CLIBNAME_BYTECODE=$(CLIBNAME)byt
 CLIBNAME_NATIVE=$(CLIBNAME)nat
 STUBSLIB_BYTECODE=lib$(CLIBNAME_BYTECODE).$(A)
 STUBSLIB_NATIVE=lib$(CLIBNAME_NATIVE).$(A)
+
+ifeq "$(SUFFIXING)" "true"
+STUBSDLL=dll$(CLIBNAME_BYTECODE)-$(TARGET)-$(BYTECODE_RUNTIME_ID)$(EXT_DLL)
+else
+STUBSDLL=dll$(CLIBNAME_BYTECODE)$(EXT_DLL)
+endif
 endif
 
 .PHONY: all allopt opt.opt # allopt and opt.opt are synonyms
@@ -95,49 +110,40 @@ lib$(CLIBNAME_BYTECODE).$(A): $(COBJS)
 lib$(CLIBNAME_NATIVE).$(A): $(COBJS)
 	$(V_OCAMLMKLIB)$(MKLIB) -oc $(CLIBNAME_NATIVE) $(COBJS_NATIVE) $(LDOPTS)
 
-INSTALL_LIBDIR_LIBNAME = $(INSTALL_LIBDIR)/$(LIBNAME)
-
 install::
-	if test -f dll$(CLIBNAME_BYTECODE)$(EXT_DLL); then \
-	  $(INSTALL_PROG) \
-	    dll$(CLIBNAME_BYTECODE)$(EXT_DLL) "$(INSTALL_STUBLIBDIR)"; \
-	fi
 ifneq "$(STUBSLIB_BYTECODE)" ""
-	$(INSTALL_DATA) $(STUBSLIB_BYTECODE) "$(INSTALL_LIBDIR)/"
+ifeq "$(SUPPORTS_SHARED_LIBRARIES)" "true"
+	$(call INSTALL_ITEMS, $(STUBSDLL), stublibs)
+endif
+	$(call INSTALL_ITEMS, $(STUBSLIB_BYTECODE), lib)
 endif
 # If installing over a previous OCaml version, ensure the library is removed
 # from the previous installation.
-	rm -f $(addprefix "$(INSTALL_LIBDIR)"/, \
-          $(LIBNAME).cma $(CMIFILES) \
-          $(CMIFILES:.cmi=.mli) $(CMIFILES:.cmi=.cmti) \
-          $(CAMLOBJS_NAT) $(LIBNAME).cmxa $(LIBNAME).cmxs $(LIBNAME).$(A))
-	$(MKDIR) "$(INSTALL_LIBDIR_LIBNAME)"
-	$(INSTALL_DATA) \
-	  $(LIBNAME).cma $(CMIFILES) META \
-	  "$(INSTALL_LIBDIR_LIBNAME)/"
+	$(call INSTALL_RM, \
+	  $(addprefix "$(INSTALL_LIBDIR)"/, \
+	  $(LIBNAME).cma $(CMIFILES) \
+	  $(CMIFILES:.cmi=.mli) $(CMIFILES:.cmi=.cmti) \
+	  $(CAMLOBJS_NAT) $(LIBNAME).cmxa $(LIBNAME).cmxs $(LIBNAME).$(A)))
+	$(call INSTALL_ITEMS, $(LIBNAME).cma $(CMIFILES) META, lib, $(LIBNAME))
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	  $(CMIFILES:.cmi=.mli) \
-          $(CMIFILES:.cmi=.cmti) \
-	  "$(INSTALL_LIBDIR_LIBNAME)/"
+	$(call INSTALL_ITEMS, $(CMIFILES:.cmi=.mli) $(CMIFILES:.cmi=.cmti), \
+	  lib, $(LIBNAME))
+endif
+ifneq "$(HEADERS)" ""
+	$(call INSTALL_ITEMS, $(HEADERS), lib, $(INSTALL_LIBDIR_CAML))
 endif
-	if test -n "$(HEADERS)"; then \
-	  $(INSTALL_DATA) $(HEADERS) "$(INSTALL_INCDIR)/"; \
-	fi
 
 installopt:
-	$(INSTALL_DATA) \
-	   $(CAMLOBJS_NAT) $(LIBNAME).cmxa $(LIBNAME).$(A) \
-	   "$(INSTALL_LIBDIR_LIBNAME)/"
-	if test -f $(LIBNAME).cmxs; then \
-	  $(INSTALL_PROG) $(LIBNAME).cmxs "$(INSTALL_LIBDIR_LIBNAME)"; \
-	fi
-	if test -f dll$(CLIBNAME_NATIVE)$(EXT_DLL); then \
-	  $(INSTALL_PROG) \
-	    dll$(CLIBNAME_NATIVE)$(EXT_DLL) "$(INSTALL_STUBLIBDIR)"; \
-	fi
+	$(call INSTALL_ITEMS, \
+	   $(CAMLOBJS_NAT) $(LIBNAME).cmxa $(LIBNAME).$(A), lib, $(LIBNAME))
+ifeq "$(SUPPORTS_SHARED_LIBRARIES)" "true"
+	$(call INSTALL_ITEMS, $(LIBNAME).cmxs, libexec, $(LIBNAME))
+ifeq "$(SUFFIXING)" "false"
+	$(call INSTALL_ITEMS, dll$(CLIBNAME_NATIVE)$(EXT_DLL), stublibs)
+endif
+endif
 ifneq "$(STUBSLIB_NATIVE)" ""
-	$(INSTALL_DATA) $(STUBSLIB_NATIVE) "$(INSTALL_LIBDIR)/"
+	$(call INSTALL_ITEMS, $(STUBSLIB_NATIVE), lib)
 endif
 
 partialclean:
diff --git a/otherlibs/dynlink/byte/dynlink.ml b/otherlibs/dynlink/byte/dynlink.ml
index 0f315d3ab0d0..a3c553e8dae5 100644
--- a/otherlibs/dynlink/byte/dynlink.ml
+++ b/otherlibs/dynlink/byte/dynlink.ml
@@ -194,7 +194,7 @@ module Bytecode = struct
         let toc_pos = input_binary_int ic in  (* Go to table of contents *)
         seek_in ic toc_pos;
         let lib = (input_value ic : library) in
-        Symtable.open_dlls lib.lib_dllibs;
+        Symtable.open_dlls ic lib;
         handle, lib.lib_units
       end else begin
         raise (DT.Error (Not_a_bytecode_file file_name))
diff --git a/otherlibs/dynlink/byte/dynlink_symtable.ml b/otherlibs/dynlink/byte/dynlink_symtable.ml
index e275a2856466..ec90f2a1c63d 100644
--- a/otherlibs/dynlink/byte/dynlink_symtable.ml
+++ b/otherlibs/dynlink/byte/dynlink_symtable.ml
@@ -89,14 +89,40 @@ let primitives : (string, int) Hashtbl.t = Hashtbl.create 100
 #52 "bytecomp/dll.ml"
 (* Extract the name of a DLLs from its external name (xxx.so or -lxxx) *)
 
-let extract_dll_name file =
-  if Filename.check_suffix file Config.ext_dll then
+let extract_dll_name (suffixed, file) =
+  if not suffixed && Filename.check_suffix file Config.ext_dll then
     Filename.chop_suffix file Config.ext_dll
-  else if String.length file >= 2 && String.sub file 0 2 = "-l" then
-    "dll" ^ String.sub file 2 (String.length file - 2)
   else
-    file (* will cause error later *)
-#100 "otherlibs/dynlink/byte/dynlink_symtable.ml"
+    let file =
+      if String.starts_with ~prefix:"-l" file then
+      "dll" ^ String.sub file 2 (String.length file - 2)
+    else
+      file
+    in
+      if suffixed then
+#104 "otherlibs/dynlink/byte/dynlink_symtable.ml"
+        (* This name must be in sync with Misc.RuntimeID.stubslib *)
+        Printf.sprintf "%s-%s-%s" file Config.target Config.bytecode_runtime_id
+#66 "bytecomp/dll.ml"
+      else
+        file
+
+#75 "bytecomp/dll.ml"
+let rebmun_cigam_amc =
+  let magic_length = String.length Config.cma_magic_number in
+  let init i = Config.cma_magic_number.[magic_length - i - 1] in
+  String.init magic_length init
+
+let read_suffixed_dllibs_from_channel ic l =
+#82 "bytecomp/dll.ml"
+  let magic_length = String.length Config.cma_magic_number in
+  match In_channel.really_input_string ic magic_length with
+  | Some magic when magic = rebmun_cigam_amc ->
+      let combine suffixed l acc = (suffixed, l)::acc in
+      List.fold_right2 combine (input_value ic : bool list) l.lib_dllibs []
+  | _ ->
+      List.map (fun l -> (false, l)) l.lib_dllibs
+#126 "otherlibs/dynlink/byte/dynlink_symtable.ml"
 (* Specialized version of [Dll.{open_dll,open_dlls,find_primitive}] for the
     execution mode. *)
 let open_dll name =
@@ -129,8 +155,8 @@ let open_dll name =
 (* Open a list of DLLs, adding them to opened_dlls.
    Raise [Failure msg] in case of error. *)
 
-let open_dlls names =
-  List.iter open_dll names
+let open_dlls ic lib =
+  List.iter open_dll (read_suffixed_dllibs_from_channel ic lib)
 
 let find_primitive prim_name =
   try Hashtbl.find primitives prim_name
@@ -233,12 +259,12 @@ let patch_object buff patchlist =
 (* Functions for toplevel use *)
 
 (* Update the in-core table of globals *)
-#237 "otherlibs/dynlink/byte/dynlink_symtable.ml"
+#263 "otherlibs/dynlink/byte/dynlink_symtable.ml"
 module Meta = struct
 #16 "bytecomp/meta.ml"
 external global_data : unit -> Obj.t array = "caml_get_global_data"
 external realloc_global_data : int -> unit = "caml_realloc_global"
-#242 "otherlibs/dynlink/byte/dynlink_symtable.ml"
+#268 "otherlibs/dynlink/byte/dynlink_symtable.ml"
 end
 #332 "bytecomp/symtable.ml"
 let update_global_table () =
@@ -264,7 +290,7 @@ external get_bytecode_sections : unit -> bytecode_sections =
 let init_toplevel () =
   let sect = get_bytecode_sections () in
   global_table := sect.symb;
-#268 "otherlibs/dynlink/byte/dynlink_symtable.ml"
+#294 "otherlibs/dynlink/byte/dynlink_symtable.ml"
   Dll.init ~dllpaths:sect.dlpt ~prims:sect.prim;
 #358 "bytecomp/symtable.ml"
   sect.crcs
@@ -317,7 +343,7 @@ let current_state () = !global_table
 #412 "bytecomp/symtable.ml"
 let hide_additions (st : global_map) =
   if st.cnt > !global_table.cnt then
-#321 "otherlibs/dynlink/byte/dynlink_symtable.ml"
+#347 "otherlibs/dynlink/byte/dynlink_symtable.ml"
     failwith "Symtable.hide_additions";
 #415 "bytecomp/symtable.ml"
   global_table :=
diff --git a/otherlibs/dynlink/byte/dynlink_symtable.mli b/otherlibs/dynlink/byte/dynlink_symtable.mli
index 686cb4c44d41..1d76e3be42fc 100644
--- a/otherlibs/dynlink/byte/dynlink_symtable.mli
+++ b/otherlibs/dynlink/byte/dynlink_symtable.mli
@@ -31,7 +31,7 @@ module Global : sig
   val description: Format.formatter -> t -> unit
 end
 
-val open_dlls : string list -> unit
+val open_dlls : in_channel -> library -> unit
 
 val patch_object:
   (char, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t ->
diff --git a/otherlibs/dynlink/dynlink_config.ml.in b/otherlibs/dynlink/dynlink_config.ml.in
index 60132fe50356..e51fa45bc383 100644
--- a/otherlibs/dynlink/dynlink_config.ml.in
+++ b/otherlibs/dynlink/dynlink_config.ml.in
@@ -24,3 +24,7 @@ let ext_dll = "." ^ {@QS@|@SO@|@QS@}
 and cmo_magic_number = {@QS@|@CMO_MAGIC_NUMBER@|@QS@}
 and cma_magic_number = {@QS@|@CMA_MAGIC_NUMBER@|@QS@}
 and cmxs_magic_number = {@QS@|@CMXS_MAGIC_NUMBER@|@QS@}
+
+let bytecode_runtime_id = {@QS@|@bytecode_runtime_id@|@QS@}
+
+let target = {@QS@|@target@|@QS@}
diff --git a/otherlibs/dynlink/dynlink_config.mli b/otherlibs/dynlink/dynlink_config.mli
index ad44848ebc20..30dbdf4df6bf 100644
--- a/otherlibs/dynlink/dynlink_config.mli
+++ b/otherlibs/dynlink/dynlink_config.mli
@@ -21,3 +21,7 @@ val ext_dll: string
 val cmo_magic_number: string
 val cma_magic_number: string
 val cmxs_magic_number: string
+
+val bytecode_runtime_id: string
+
+val target : string
diff --git a/otherlibs/systhreads/Makefile b/otherlibs/systhreads/Makefile
index 64d41cc19d66..617093bb4ecd 100644
--- a/otherlibs/systhreads/Makefile
+++ b/otherlibs/systhreads/Makefile
@@ -14,6 +14,7 @@
 #**************************************************************************
 
 ROOTDIR=../..
+SUBDIR_NAME=otherlibs/systhreads
 
 include $(ROOTDIR)/Makefile.common
 include $(ROOTDIR)/Makefile.best_binaries
@@ -27,6 +28,12 @@ CAMLC=$(BEST_OCAMLC) $(LIBS)
 CAMLOPT=$(BEST_OCAMLOPT) $(LIBS)
 
 MKLIB=$(OCAMLRUN) $(ROOTDIR)/tools/ocamlmklib$(EXE)
+ifeq "$(SUFFIXING)" "true"
+MKLIB += -suffixed
+DLLTHREADS = dllthreads-$(TARGET)-$(BYTECODE_RUNTIME_ID)$(EXT_DLL)
+else
+DLLTHREADS = dllthreads$(EXT_DLL)
+endif
 COMPFLAGS=-w +33..39 -warn-error +A -g -bin-annot
 ifeq "$(FLAMBDA)" "true"
 OPTCOMPFLAGS += -O3
@@ -97,30 +104,22 @@ clean: partialclean
 distclean: clean
 	rm -f META
 
-INSTALL_THREADSLIBDIR=$(INSTALL_LIBDIR)/$(LIBNAME)
-
 install:
-	if test -f dllthreads$(EXT_DLL); then \
-	  $(INSTALL_PROG) dllthreads$(EXT_DLL) "$(INSTALL_STUBLIBDIR)"; \
-	fi
-	$(INSTALL_DATA) libthreads.$(A) "$(INSTALL_LIBDIR)"
-	$(MKDIR) "$(INSTALL_THREADSLIBDIR)"
-	$(INSTALL_DATA) \
-	  $(CMIFILES) threads.cma META \
-	  "$(INSTALL_THREADSLIBDIR)"
+ifeq "$(SUPPORTS_SHARED_LIBRARIES)" "true"
+	$(call INSTALL_ITEMS, $(DLLTHREADS), stublibs)
+endif
+	$(call INSTALL_ITEMS, libthreads.$(A), lib)
+	$(call INSTALL_ITEMS, $(CMIFILES) threads.cma META, lib, $(LIBNAME))
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	  $(CMIFILES:.cmi=.cmti) \
-	  "$(INSTALL_THREADSLIBDIR)"
-	$(INSTALL_DATA) $(MLIFILES) "$(INSTALL_THREADSLIBDIR)"
+	$(call INSTALL_ITEMS, $(CMIFILES:.cmi=.cmti), lib, $(LIBNAME))
+	$(call INSTALL_ITEMS, $(MLIFILES), lib, $(LIBNAME))
 endif
-	$(INSTALL_DATA) caml/threads.h "$(INSTALL_INCDIR)"
+	$(call INSTALL_ITEMS, caml/threads.h, lib, $(INSTALL_LIBDIR_CAML))
 
 installopt:
-	$(INSTALL_DATA) libthreadsnat.$(A) "$(INSTALL_LIBDIR)"
-	$(INSTALL_DATA) \
-	  $(THREADS_NCOBJS) threads.cmxa threads.$(A) \
-	  "$(INSTALL_THREADSLIBDIR)"
+	$(call INSTALL_ITEMS, libthreadsnat.$(A), lib)
+	$(call INSTALL_ITEMS, $(THREADS_NCOBJS) threads.cmxa threads.$(A), \
+	  lib, $(LIBNAME))
 
 %.cmi: %.mli
 	$(V_OCAMLC)$(CAMLC) -c $(COMPFLAGS) $<
diff --git a/release-info/howto.md b/release-info/howto.md
index 3b67474ac676..79b75326e0a8 100644
--- a/release-info/howto.md
+++ b/release-info/howto.md
@@ -165,6 +165,10 @@ git branch $BRANCH
 
 # update build-aux/ocaml_version.m4 with the new future branch,
 #   4.07.0+dev1-2018-06-26 => 4.08.0+dev0-2018-06-30
+# Also increment OCAML__RELEASE_NUMBER in build-aux/ocaml_version.m4
+#   If the major version number is changing, the logic in p_runtime_id in
+#   tools/objinfo.ml mapping release number to major/minor version will need
+#   altering.
 # Update ocaml-variants.opam with new version.
 make -B configure
 # Add a "Working version" section" to Changes
diff --git a/runtime/Mangling.md b/runtime/Mangling.md
new file mode 100644
index 000000000000..fd2f7c30abb0
--- /dev/null
+++ b/runtime/Mangling.md
@@ -0,0 +1,135 @@
+# Filename Mangling
+
+## Background
+
+OCaml compiler installations exist in isolation. When running the compiler, it
+is assumed that the caller will have configured the environment of the compiler
+such that files and settings related to other compiler installations will not
+interfere.
+
+This is not true of the runtime. Shared libraries are loaded from a global
+namespace (dynamically loaded bytecode stub libraries and the shared versions of
+both the native and bytecode runtimes) and programs may be searched in a global
+PATH. To allow programs compiled against different coinstalled versions of the
+runtime to be executed, a name mangling scheme is used for the runtime's
+executables and shared libraries.
+
+## Filename Mangling
+
+Filenames are mangled using one or both of two pieces of configuration
+information. The first is the standard "autoconf" triplet on which the runtime
+executes (e.g. `x86_64-pc-linux-gnu`). The other is a summary of the runtime
+version and configuration called the Runtime ID. This information is a series of
+bits encoded in base32 using the alphabet `[0-9a-v]` and with the quintets laid
+out little-endian.
+
+Mangling is applied to the name of any file which will be searched for at
+runtime:
+
+- `ocamlrun` (and variants) are triplet-prefixed and Bytecode-suffixed. For
+  example, `x86_64-pc-linux-gnu-ocamlrun-a140` is OCaml 5.5 configured with
+  `--disable-flat-float-array` on 64-bit Intel/AMD Linux. A symbolic link is
+  still created for `ocamlrun` pointing to this mangled name. Additionally, a
+  symbolic link is also created for `ocamlrun-a140`, using the Zinc-suffix.
+- C stub libraries loaded by both the bytecode runtime and bytecode `Dynlink`
+  library are triplet- and Bytecode-suffixed. For example,
+  `dllunixbyt-x86_64-pc-linux-gnu-a140.so` contains the C stubs for the Unix
+  library for OCaml 5.5 configured with `--disable-flat-float-array` on 64-bit
+  Intel/AMD Linux.
+- Shared versions of the bytecode and native runtimes (`libcamlrun_shared.so`
+  and `libasmrun_shared.so`) are triplet- and Bytecode/Native-suffixed
+  respectively. For example, `libasmrun-x86_64-pc-linux-gnu-a1k0.so` and
+  `libcamlrun-x86_64-pc-linux-gnu-a140.so` are OCaml 5.5 configured with
+  `--disable-flat-float-array` and `--enable-tsan` on 64-bit Intel/AMD Linux
+  (note the **tsan** bit not being set for the name of libcamlrun).
+  Additionally, symbolic links are also created for `libasmrun_shared.so` and
+  `libcamlrun_shared.so`.
+
+## Runtime ID
+
+A Runtime ID is a bit string describing a given OCaml runtime. At present,
+20 bits are used, but the format is intended to be trivially extensible.
+Ultimately, the only requirement is that each version and configuration
+generates some kind of unique identifier which can then be used in filenames.
+
+- Bit 0 (**dev**): Development bit. This should be set for development versions
+  of OCaml or for customised compilers. If it is not set, the compiler should be
+  an unaltered official release.
+- Bits 1-6 (**release**): OCaml release number. This is incremented for each
+  minor release of the compiler, with OCaml 3.12.0[^1] being release 0. At
+  present, the ordering of release numbers matches the semantic ordering of the
+  version numbers, but this is not guaranteed and should not be assumed[^2].
+- Bits 7-11 (**reserved**): Number of reserved bits in the OCaml value header.
+  This is the number passed to `--enable-reserved-header-bits` when the compiler
+  distribution was configured.
+- Bit 12 (**no-flat-float-array**): Set if the compiler distribution was
+  configured with `--disable-flat-float-array`.
+- Bit 13 (**fp**): Set if the compiler distribution was configured with
+  `--enable-frame-pointers`. Affects the **native** runtime only.
+- Bit 14 (**tsan**): For OCaml 5.2 onwards, set if the compiler distribution was
+  configured with `--enable-tsan`. Prior to OCaml 5.2, set if the compiler
+  distribution was configured with `--enable-spacetime` (this option was removed
+  in OCaml 4.12, meaning this bit is always unset for OCaml 4.12-5.1). Affects
+  the **native** runtime only.
+- Bit 15 (**int31**): Set if the runtime uses 31-bit `int` values (i.e. runtimes
+  running on 32-bit systems).
+- Bit 16 (**static**): Set if the runtime does not support shared libraries,
+  meaning dynamic loading of C code is not supported in bytecode, and native
+  dynlink is not supported at all.
+- Bit 17 (**no-compression**): For OCaml 5.1 onwards, set if the runtime does
+  not support compressed marshalling. Prior to OCaml 5.1, set if the compiler
+  distribution was configured with `--enable-naked-pointers` (this bit was
+  always unset for OCaml 5.0, since it supports neither naked pointers nor
+  compressed marshalling).
+- Bit 18 (**ansi**): Set if the compiler distribution was configured with the
+  legacy support `WINDOWS_UNICODE=ansi`.
+- Bit 19 (**mutable-string**): Set if the compiler distribution was configured
+  with `--disable-force-safe-string`. This option was removed in OCaml 5.0, and
+  the bit is available for re-use. When this bit is unset, strings are
+  guaranteed to be immutable.
+
+The bit descriptions are designed such that the default configuration of the
+latest version of the compiler has unset bits. The ordering of the bits is
+designed to mean ID values in the same version of OCaml will usually have the
+same opening sequence of characters (since `--enable-reserved-header-bits` is
+now rarely used) and laying out the characters little-endian in the mangling
+scheme means that the opening two characters of the Runtime ID define its
+version (and consequently its length, should that change in future).
+
+[^1]: OCaml 3.12.0 was the first version where `ocamlrun` supported the `-vnum`
+argument; the original author had a fantasy of backporting the scheme to the
+entire 4.x series, but following some therapy stopped at 4.08. The release
+numbering persists to allow for future madness.
+[^2]: In particular, should there be any additional releases in the OCaml 4.x
+series, these will have higher release numbers than releases already made in the
+OCaml 5.x series.
+
+## Masks
+
+A particular configuration of the compiler has one Runtime ID, but this is used
+in three different contexts where certain bits are masked out:
+
+1. _Bytecode Mask_: masks out bits which are only ever set by the native runtime
+   (at present, **fp** and **tsan**).
+2. _Native Mask_: masks out bits which are only ever set by the bytecode runtime
+   (at present there aren't any).
+3. _Zinc Mask_: masks out bits which are not related to bytecode portability.
+   Where the _Bytecode_ and _Native_ masks relate to _runtimes_, the _Zinc_ mask
+   relates to _bytecode images_. The Zinc ID therefore includes:
+   - **release** and **dev** (a given bytecode image targets a specific version
+     of OCaml)
+   - **no-flat-float-array** (code compiled assuming that float arrays are boxed
+     will segfault on runtimes which unbox them)
+   - **int31**, **static**, and **no-compression** (a bytecode image using
+     63-bit integers, dynamically loaded C stubs and compressed marshalling will
+     be rejected by an interpreter which doesn't support any of these features)
+
+Note that the inclusion of a bit in a mask is determined by whether that
+property affects the ability to load and execute the code, rather than whether
+it is semantically affected by it. For example, the **reserved** bits affects
+the value representation, and therefore both runtimes. It does not directly
+affect bytecode (although a bytecode program may use unsafe features to observe
+it). **reserved** is therefore part of both the _Bytecode_ and _Native Masks_,
+but not part of the _Zinc Mask_. Similarly, although **no-flat-float-array**
+affects code generation for bytecode, **mutable-string** never did, and so would
+not be included in the _Zinc Mask_.
diff --git a/runtime/backtrace_byt.c b/runtime/backtrace_byt.c
index e8cb4b3999dd..982dfe47eba1 100644
--- a/runtime/backtrace_byt.c
+++ b/runtime/backtrace_byt.c
@@ -451,7 +451,7 @@ static void read_main_debug_info(struct debug_info *di)
   CAMLassert(di->already_read == 0);
   di->already_read = 1;
 
-  /* At the moment, bytecode programs built with --output-complete-exe
+  /* At the moment, bytecode programs built with -output-complete-exe
      do not contain any debug info.
 
      See  https://github.com/ocaml/ocaml/issues/9344 for details.
diff --git a/runtime/caml/dynlink.h b/runtime/caml/dynlink.h
index d5f7170e6fcb..a7441fcc0e4f 100644
--- a/runtime/caml/dynlink.h
+++ b/runtime/caml/dynlink.h
@@ -41,11 +41,10 @@ extern void caml_build_primitive_table_builtin(void);
 /* Unload all the previously loaded shared libraries */
 extern void caml_free_shared_libs(void);
 
-/* Return the effective location of the standard library */
-extern char_os * caml_get_stdlib_location(void);
-
-/* Parse ld.conf and add the lines read to caml_shared_libs_path */
-extern char_os * caml_parse_ld_conf(void);
+/* If found, parse $OCAMLLIB/ld.conf, $CAMLLIB/ld.conf and stdlib/ld.conf in
+   that order and add the lines read to table. */
+extern char_os * caml_parse_ld_conf(const char_os * stdlib,
+                                    struct ext_table * table);
 
 #endif /* CAML_INTERNALS */
 
diff --git a/runtime/caml/exec.h.in b/runtime/caml/exec.h.in
index 333af64ddede..9572dd88e1ac 100644
--- a/runtime/caml/exec.h.in
+++ b/runtime/caml/exec.h.in
@@ -20,6 +20,8 @@
 
 #ifdef CAML_INTERNALS
 
+#include <stdint.h>
+
 /* Executable bytecode files are composed of a number of sections,
    identified by 4-character names.  A table of contents at the
    end of the file lists the section names along with their sizes,
diff --git a/runtime/caml/version.h.in b/runtime/caml/version.h.in
index bfe5d70957dc..66c7611bc4a5 100644
--- a/runtime/caml/version.h.in
+++ b/runtime/caml/version.h.in
@@ -22,3 +22,4 @@
 #undef OCAML_VERSION_EXTRA
 #undef OCAML_VERSION
 #undef OCAML_VERSION_STRING
+#undef OCAML_RELEASE_NUMBER
diff --git a/runtime/dynlink.c b/runtime/dynlink.c
index c06f8adb9aac..621b71dea830 100644
--- a/runtime/dynlink.c
+++ b/runtime/dynlink.c
@@ -43,12 +43,12 @@
 
 #include "build_config.h"
 
-#ifndef NATIVE_CODE
-
 #ifndef O_BINARY
 #define O_BINARY 0
 #endif
 
+#ifndef NATIVE_CODE
+
 /* The table of primitives */
 struct ext_table caml_prim_table;
 
@@ -78,23 +78,63 @@ static c_primitive lookup_primitive(char * name)
   return NULL;
 }
 
+#endif /* NATIVE_CODE */
+
 /* Parse the ld.conf file and add the directories
    listed there to the search path */
 
 #define LD_CONF_NAME T("ld.conf")
 
-CAMLexport char_os * caml_get_stdlib_location(void)
+#ifdef _WIN32
+
+#define CAML_DIR_SEP T("\\")
+#define Is_separator(c) (c == '\\' || c == '/')
+
+#else
+
+#define CAML_DIR_SEP T("/")
+#define Is_separator(c) (c == '/')
+
+#endif /* _WIN32 */
+
+/* Return a copy of [path], interpreting explicit-relative paths relative to
+   [root]. [root] must not end with a directory separator and is expected to be
+   absolute. The result of this function can never be ".", ".." or a path
+   beginning "./" or "../". Note that the function does not necessarily
+   canonicalise the path. */
+static char_os *make_relative_path_absolute(char_os *path, char_os *root)
 {
-  char_os * stdlib;
-  stdlib = caml_secure_getenv(T("OCAMLLIB"));
-  if (stdlib == NULL) stdlib = caml_secure_getenv(T("CAMLLIB"));
-  if (stdlib == NULL) stdlib = OCAML_STDLIB_DIR;
-  return stdlib;
+  if (path[0] == '.') {
+    if (path[1] == '\0') {
+      /* path is exactly "." => return root */
+      return caml_stat_strdup_os(root);
+    } else if (Is_separator(path[1])) {
+      /* path is exactly "./" or begins "./". In both cases, replace the "."
+         with root */
+      return caml_stat_strconcat_os(2, root, (path + 1));
+    } else if (path[1] == '.' && (path[2] == '\0' || Is_separator(path[2]))) {
+      /* path is either exactly ".." or begins "../" => prefix it with root
+         (which has no trailing separator) */
+      return caml_stat_strconcat_os(3, root, CAML_DIR_SEP, path);
+    } else {
+      /* path is not explicit-relative, but simply begins with a dot
+           => return a copy */
+      return caml_stat_strdup_os(path);
+    }
+  } else {
+    /* path is not explicit-relative => return a copy */
+    return caml_stat_strdup_os(path);
+  }
 }
 
-CAMLexport char_os * caml_parse_ld_conf(void)
+CAMLexport char_os * caml_parse_ld_conf(const char_os * stdlib,
+                                        struct ext_table *table)
 {
-  char_os * stdlib, * ldconfname, * wconfig, * p, * q;
+  const char_os * const locations[3] = {
+    caml_secure_getenv(T("OCAMLLIB")),
+    caml_secure_getenv(T("CAMLLIB")),
+    stdlib};
+  char_os * libroot, * ldconfname, * wconfig, * p, * q;
   char * config;
 #ifdef _WIN32
   struct _stati64 st;
@@ -102,48 +142,127 @@ CAMLexport char_os * caml_parse_ld_conf(void)
   struct stat st;
 #endif
   int ldconf, nread;
+  size_t length = 0;
+  struct ext_table entries;
+
+  /* Use a temporary ext_table to hold the individually-allocated entries */
+  caml_ext_table_init(&entries, 8);
+  for (int i = 0; i < sizeof(locations) / sizeof(locations[0]); i++) {
+    if (locations[i] != NULL) {
+      libroot = caml_stat_strdup_os(locations[i]);
+      size_t libroot_length = strlen_os(libroot);
+      while (libroot_length > 0 && Is_separator(libroot[libroot_length - 1]))
+        libroot[--libroot_length] = '\0';
+      ldconfname =
+        caml_stat_strconcat_os(3, libroot, CAML_DIR_SEP, LD_CONF_NAME);
+      if (stat_os(ldconfname, &st) == -1) {
+        caml_stat_free(ldconfname);
+        caml_stat_free(libroot);
+        continue;
+      }
+      ldconf = open_os(ldconfname, O_RDONLY | O_BINARY, 0);
+      if (ldconf == -1)
+        caml_fatal_error("cannot read loader config file %s",
+                             caml_stat_strdup_of_os(ldconfname));
+      config = caml_stat_alloc(st.st_size + 1);
+      nread = read(ldconf, config, st.st_size);
+      if (nread == -1)
+        caml_fatal_error
+          ("error while reading loader config file %s",
+           caml_stat_strdup_of_os(ldconfname));
+      close(ldconf);
+      config[nread] = 0;
+      wconfig = caml_stat_strdup_to_os(config);
+      caml_stat_free(config);
+      caml_stat_free(ldconfname);
+
+      p = wconfig;
+      while (*p != '\0') {
+        for (q = p; *q != '\0' && *q != '\n'; q++) /*nothing*/;
+        char_os *r = q;
+        if (*q == '\n') {
+          r++;
+          /* Ignore any trailing CR characters, so that CR*LF is uniformly
+             treated as a single LF. */
+          while (q > p && *(q - 1) == '\r')
+            q--;
+        }
+        *q = '\0';
+        char_os *entry = make_relative_path_absolute(p, libroot);
+        length += strlen_os(entry) + 1;
+        caml_ext_table_add(&entries, entry);
+        p = r;
+      }
 
-  stdlib = caml_get_stdlib_location();
-  ldconfname = caml_stat_strconcat_os(3, stdlib, T("/"), LD_CONF_NAME);
-  if (stat_os(ldconfname, &st) == -1) {
-    caml_stat_free(ldconfname);
-    return NULL;
-  }
-  ldconf = open_os(ldconfname, O_RDONLY, 0);
-  if (ldconf == -1)
-    caml_fatal_error("cannot read loader config file %s",
-                         caml_stat_strdup_of_os(ldconfname));
-  config = caml_stat_alloc(st.st_size + 1);
-  nread = read(ldconf, config, st.st_size);
-  if (nread == -1)
-    caml_fatal_error
-      ("error while reading loader config file %s",
-       caml_stat_strdup_of_os(ldconfname));
-  config[nread] = 0;
-  wconfig = caml_stat_strdup_to_os(config);
-  caml_stat_free(config);
-  q = wconfig;
-  for (p = wconfig; *p != 0; p++) {
-    if (*p == '\n') {
-      *p = 0;
-      caml_ext_table_add(&caml_shared_libs_path, q);
-      q = p + 1;
+      caml_stat_free(wconfig);
+      caml_stat_free(libroot);
     }
   }
-  if (q < p) caml_ext_table_add(&caml_shared_libs_path, q);
-  close(ldconf);
-  caml_stat_free(ldconfname);
-  return wconfig;
+
+  /* Now concatenate them all and load the search path */
+  char_os *result = caml_stat_alloc(length * sizeof(char_os));
+  p = result;
+  for (int i = 0; i < entries.size; i++) {
+    char_os *entry = entries.contents[i];
+    length = strlen_os(entry) + 1;
+    memcpy(p, entry, length * sizeof(char_os));
+    caml_ext_table_add(table, p);
+    p += length;
+  }
+  caml_ext_table_free(&entries, 1);
+
+  return result;
+}
+
+/* Exposes caml_parse_ld_conf as a primitive for the bytecode compiler, saving
+   the duplication of the logic within the bytecode compiler. */
+CAMLprim value caml_dynlink_parse_ld_conf(value vstdlib)
+{
+  CAMLparam1(vstdlib);
+  CAMLlocal2(list, str);
+
+  char_os *stdlib = caml_stat_strdup_to_os(String_val(vstdlib));
+  struct ext_table table;
+  caml_ext_table_init(&table, 8);
+  char_os *tofree = caml_parse_ld_conf(stdlib, &table);
+  caml_stat_free(stdlib);
+
+  list = Val_emptylist;
+  for (int i = table.size - 1; i >= 0; i--) {
+    str = caml_copy_string_of_os(table.contents[i]);
+    list = caml_alloc_2(Tag_cons, str, list);
+  }
+
+  caml_ext_table_free(&table, 0);
+  caml_stat_free(tofree);
+
+  CAMLreturn(list);
 }
 
+#ifndef NATIVE_CODE
+
 /* Open the given shared library and add it to shared_libs.
    Abort on error. */
 static void open_shared_lib(char_os * name)
 {
-  char_os * realname;
+  char_os * realname, * suffixed = NULL;
   char * u8;
   void * handle;
 
+  if (*name == '\0')
+    caml_fatal_error("corrupt DLLS section");
+
+  if (*name == '-') {
+    char * suffix =
+      caml_stat_strconcat(4, "-", HOST, "-", BYTECODE_RUNTIME_ID);
+    char_os * suffix_os = caml_stat_strdup_to_os(suffix);
+    name = suffixed = caml_stat_strconcat_os(2, name + 1, suffix_os);
+    caml_stat_free(suffix_os);
+    caml_stat_free(suffix);
+  } else {
+    name++;
+  }
+
   realname = caml_search_dll_in_path(&caml_shared_libs_path, name);
   u8 = caml_stat_strdup_of_os(realname);
   caml_gc_message(0x100, "Loading shared library %s\n", u8);
@@ -160,9 +279,12 @@ static void open_shared_lib(char_os * name)
       caml_dlerror()
     );
   caml_ext_table_add(&shared_libs, handle);
+  caml_stat_free(suffixed);
   caml_stat_free(realname);
 }
 
+extern const char_os *caml_runtime_standard_library_effective;
+
 /* Build the table of primitives, given a search path and a list
    of shared libraries (both 0-separated in a char array).
    Abort the runtime system on error. */
@@ -174,6 +296,8 @@ void caml_build_primitive_table(char_os * lib_path,
      - directories specified on the command line with the -I option
      - directories specified in the CAML_LD_LIBRARY_PATH
      - directories specified in the executable
+     - directories specified in OCAMLLIB/ld.conf
+     - directories specified in CAMLLIB/ld.conf
      - directories specified in the file <stdlib>/ld.conf
 
      caml_shared_libs_path and caml_prim_name_table are not freed afterwards:
@@ -183,7 +307,8 @@ void caml_build_primitive_table(char_os * lib_path,
   if (lib_path != NULL)
     for (char_os *p = lib_path; *p != 0; p += strlen_os(p) + 1)
       caml_ext_table_add(&caml_shared_libs_path, p);
-  caml_parse_ld_conf();
+  caml_parse_ld_conf(caml_runtime_standard_library_effective,
+                     &caml_shared_libs_path);
   /* Open the shared libraries */
   caml_ext_table_init(&shared_libs, 8);
   if (libs != NULL)
diff --git a/runtime/gen_primsc.sh b/runtime/gen_primsc.sh
index c18ab95a0987..95c6a7dee98e 100755
--- a/runtime/gen_primsc.sh
+++ b/runtime/gen_primsc.sh
@@ -28,9 +28,13 @@ esac
 cat <<'EOF'
 /* Generated file, do not edit */
 
+#include <stdbool.h>
+
 #define CAML_INTERNALS
 #include "caml/mlvalues.h"
 #include "caml/prims.h"
+#include "caml/startup.h"
+#include "build_config.h"
 
 EOF
 
@@ -61,3 +65,13 @@ echo
 echo 'const char * const caml_names_of_builtin_cprim[] = {'
 sed -e 's/.*/  "&",/' "$primitives"
 echo '  0 };'
+
+# ocamlrun values for symbols which are provided by the bytecode linker
+# - ocamlrun is able to use any of the mechanisms to load the bytecode
+# - caml_runtime_standard_library_default for bytecode images on this runtime
+cat <<'EOF'
+
+enum caml_byte_program_mode caml_byte_program_mode = STANDARD;
+const bool caml_byte_program_mode_custom = false;
+const char_os *caml_runtime_standard_library_default = OCAML_STDLIB_DIR;
+EOF
diff --git a/runtime/startup_byt.c b/runtime/startup_byt.c
index ffb4eb0bebdd..f2be3343b73d 100644
--- a/runtime/startup_byt.c
+++ b/runtime/startup_byt.c
@@ -20,6 +20,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>
 #include "caml/config.h"
@@ -72,6 +73,10 @@
 #define SEEK_END 2
 #endif
 
+extern const char_os *caml_runtime_standard_library_default;
+
+const char_os * caml_runtime_standard_library_effective = NULL;
+
 static char magicstr[EXEC_MAGIC_LENGTH+1];
 
 /* Print the specified error message followed by an end-of-line and exit */
@@ -113,8 +118,6 @@ int caml_read_trailer(int fd, struct exec_trailer *trail)
       ? 0 : WRONG_MAGIC;
 }
 
-enum caml_byte_program_mode caml_byte_program_mode = STANDARD;
-
 int caml_attempt_open(char_os **name, struct exec_trailer *trail,
                       int do_open_script)
 {
@@ -374,6 +377,15 @@ static int parse_command_line(char_os **argv)
   return i;
 }
 
+static const char_os * get_stdlib_location(void)
+{
+  const char_os * stdlib;
+  stdlib = caml_secure_getenv(T("OCAMLLIB"));
+  if (stdlib == NULL) stdlib = caml_secure_getenv(T("CAMLLIB"));
+  if (stdlib == NULL) stdlib = caml_runtime_standard_library_effective;
+  return stdlib;
+}
+
 /* Print the configuration of the runtime to stdout; memory allocated is not
    freed, since the runtime will terminate after calling this. */
 static void do_print_config(void)
@@ -383,13 +395,14 @@ static void do_print_config(void)
   /* Print the runtime configuration */
   printf("version: %s\n", OCAML_VERSION_STRING);
   printf("standard_library_default: %s\n",
-         caml_stat_strdup_of_os(OCAML_STDLIB_DIR));
+         caml_stat_strdup_of_os(caml_runtime_standard_library_default));
   printf("standard_library: %s\n",
-         caml_stat_strdup_of_os(caml_get_stdlib_location()));
+         caml_stat_strdup_of_os(get_stdlib_location()));
   printf("int_size: %d\n", 8 * (int)sizeof(value));
   printf("word_size: %d\n", 8 * (int)sizeof(value) - 1);
   printf("os_type: %s\n", OCAML_OS_TYPE);
   printf("host: %s\n", HOST);
+  printf("bytecode_runtime_id: %s\n", BYTECODE_RUNTIME_ID);
   printf("flat_float_array: %s\n",
 #ifdef FLAT_FLOAT_ARRAY
          "true");
@@ -420,7 +433,8 @@ static void do_print_config(void)
 
   /* Parse ld.conf and print the effective search path */
   puts("shared_libs_path:");
-  caml_parse_ld_conf();
+  caml_parse_ld_conf(caml_runtime_standard_library_effective,
+                     &caml_shared_libs_path);
   for (int i = 0; i < caml_shared_libs_path.size; i++) {
     dir = caml_shared_libs_path.contents[i];
     if (dir[0] == 0)
@@ -445,17 +459,24 @@ extern void caml_install_invalid_parameter_handler(void);
 
 #endif
 
+CAMLextern char_os *caml_locate_standard_library (const char_os *exe_name,
+                                                  const char_os *stdlib_default,
+                                                  char_os **dirname);
+
 /* Main entry point when loading code from a file */
 
+extern const bool caml_byte_program_mode_custom;
+extern char_os *caml_standard_library_default;
+
 CAMLexport void caml_main(char_os **argv)
 {
-  int fd, pos;
+  int fd = -1, pos;
   struct exec_trailer trail;
   struct channel * chan;
   value res;
   char * req_prims;
   char_os * shared_lib_path, * shared_libs;
-  char_os * exe_name, * proc_self_exe;
+  char_os * exe_name, * proc_self_exe, * argv0;
 
   /* Determine options */
   caml_parse_ocamlrunparam();
@@ -476,9 +497,21 @@ CAMLexport void caml_main(char_os **argv)
   /* Determine position of bytecode file */
   pos = 0;
 
-  /* First, try argv[0] (when ocamlrun is called by a bytecode program) */
-  exe_name = argv[0];
-  fd = caml_attempt_open(&exe_name, &trail, 0);
+  argv0 = proc_self_exe = caml_executable_name();
+
+  /* In APPENDED mode (i.e. with -custom), we always want to load the bytecode
+     from the running executable, and argv[0] should never be used. However,
+     some platforms still don't implement caml_executable_name, so there is an
+     escape hatch here to fallback to checking argv[0] if proc_self_exe is
+     NULL.
+     For STANDARD mode (i.e. the current executable is ocamlrun), argv[0] is
+     tried first, as this should be the path to shebang-script/executable
+     originally executed by the user. */
+  CAMLassert(caml_byte_program_mode != COMPLETE_EXE);
+  if (!caml_byte_program_mode_custom || proc_self_exe == NULL) {
+    exe_name = argv[0];
+    fd = caml_attempt_open(&exe_name, &trail, 0);
+  }
 
   /* Little grasshopper wonders why we do that at all, since
      "The current executable is ocamlrun itself, it's never a bytecode
@@ -486,14 +519,26 @@ CAMLexport void caml_main(char_os **argv)
      With -custom, we have an executable that is ocamlrun itself
      concatenated with the bytecode.  So, if the attempt with argv[0]
      failed, it is worth trying again with executable_name. */
-  if (fd < 0 && (proc_self_exe = caml_executable_name()) != NULL) {
-    exe_name = proc_self_exe;
-    fd = caml_attempt_open(&exe_name, &trail, 0);
+  if (caml_byte_program_mode_custom || fd < 0) {
+    if (proc_self_exe != NULL) {
+      exe_name = proc_self_exe;
+      fd = caml_attempt_open(&exe_name, &trail, 0);
+    }
+    if (fd < 0 && caml_byte_program_mode_custom)
+      error("unable to open file '%s'", caml_stat_strdup_of_os(exe_name));
   }
 
+  if (argv0 == NULL)
+    argv0 = caml_search_exe_in_path(exe_name);
+
   if (fd < 0) {
     pos = parse_command_line(argv);
     if (caml_params->print_config) {
+      caml_runtime_standard_library_effective =
+        caml_locate_standard_library(argv0,
+                                     caml_runtime_standard_library_default,
+                                     NULL);
+
       do_print_config();
       exit(0);
     }
@@ -524,6 +569,24 @@ CAMLexport void caml_main(char_os **argv)
   }
   /* Read the table of contents (section descriptors) */
   caml_read_section_descriptors(fd, &trail);
+
+  caml_runtime_standard_library_effective =
+    caml_locate_standard_library(argv0,
+                                 caml_runtime_standard_library_default, NULL);
+  if (argv0 != proc_self_exe)
+    caml_stat_free(argv0);
+
+  /* Load the embedded overridden caml_standard_library_default value, if one is
+     available. Note that although -custom executables come through this
+     mechanism, they don't define OSLD sections because
+     caml_runtime_standard_library_default and caml_standard_library_default are
+     fundamentally equal and caml_runtime_standard_library_default is set when
+     the -custom executable is linked. */
+  char_os *image_standard_library_default =
+    read_section_to_os(fd, &trail, "OSLD");
+  if (image_standard_library_default != NULL)
+    caml_standard_library_default = image_standard_library_default;
+
   /* Initialize the abstract machine */
   caml_init_gc ();
 
@@ -622,6 +685,10 @@ CAMLexport value caml_startup_code_exn(
   exe_name = caml_executable_name();
   if (exe_name == NULL) exe_name = caml_search_exe_in_path(argv[0]);
 
+  caml_runtime_standard_library_effective =
+    caml_locate_standard_library(exe_name,
+                                 caml_runtime_standard_library_default, NULL);
+
   Caml_state->external_raise = NULL;
   /* Setup signal handling */
   caml_init_signals();
diff --git a/runtime/sys.c b/runtime/sys.c
index 3356664ecdbd..edb99c8918d4 100644
--- a/runtime/sys.c
+++ b/runtime/sys.c
@@ -700,6 +700,53 @@ CAMLprim value caml_sys_const_backend_type(value unit)
 {
   return Val_int(1); /* Bytecode backed */
 }
+
+/* The native code linker doesn't synthesise calls to this primitive, instead
+   putting the required string statically in caml_standard_library_nat if any of
+   the compilation units use %standard_library_default. The primitive is omitted
+   completely in libasmrun as there are no other existing instances in the
+   native runtime where OCAML_STDLIB_DIR ends up being embedded. */
+#ifndef NATIVE_CODE
+/* If this remains unset then caml_runtime_standard_library_default is used */
+char_os *caml_standard_library_default = NULL;
+
+extern const char_os *caml_runtime_standard_library_default;
+
+CAMLprim value caml_sys_const_standard_library_default(value unit)
+{
+  return caml_copy_string_of_os(
+    caml_standard_library_default ? caml_standard_library_default
+                                  : caml_runtime_standard_library_default);
+}
+#endif
+
+CAMLextern char_os *caml_locate_standard_library (const char_os *exe_name,
+                                                  const char_os *stdlib_default,
+                                                  char_os **dirname);
+
+CAMLprim value caml_sys_get_stdlib_dirs(value vstdlib_default)
+{
+  CAMLparam1(vstdlib_default);
+  CAMLlocal3(result, eff, root_dir);
+
+  char_os *stdlib_default = caml_stat_strdup_to_os(String_val(vstdlib_default));
+  char_os *root = NULL, *stdlib;
+
+  stdlib =
+    caml_locate_standard_library(caml_params->exe_name, stdlib_default, &root);
+
+  eff = caml_copy_string_of_os(stdlib);
+  if (root == NULL) {
+    root_dir = Val_none;
+  } else {
+    root_dir = caml_copy_string_of_os(root);
+    root_dir = caml_alloc_some(root_dir);
+  }
+  result = caml_alloc_2(0, eff, root_dir);
+
+  CAMLreturn(result);
+}
+
 CAMLprim value caml_sys_get_config(value unit)
 {
   CAMLparam0 ();   /* unit is unused */
diff --git a/runtime/sys_int.h.in b/runtime/sys_int.h.in
new file mode 100644
index 000000000000..d96af93b011f
--- /dev/null
+++ b/runtime/sys_int.h.in
@@ -0,0 +1,22 @@
+/**************************************************************************/
+/*                                                                        */
+/*                                 OCaml                                  */
+/*                                                                        */
+/*             Xavier Leroy, projet Cristal, INRIA Rocquencourt           */
+/*                                                                        */
+/*   Copyright 1996 Institut National de Recherche en Informatique et     */
+/*     en Automatique.                                                    */
+/*                                                                        */
+/*   All rights reserved.  This file is distributed under the terms of    */
+/*   the GNU Lesser General Public License version 2.1, with the          */
+/*   special exception on linking described in the file LICENSE.          */
+/*                                                                        */
+/**************************************************************************/
+
+/* Operating system and standard library configuration. */
+
+#undef HAS_STRLCPY
+
+#undef HAS_LIBGEN_H
+
+/* Define HAS_LIBGEN_H if you have /usr/include/libgen.h. */
diff --git a/runtime/unix.c b/runtime/unix.c
index e19d5a26a86d..5e62839e143e 100644
--- a/runtime/unix.c
+++ b/runtime/unix.c
@@ -28,6 +28,7 @@
 #include <sys/ioctl.h>
 #include <sys/types.h>
 #include "caml/config.h"
+#include "sys_int.h"
 #ifdef HAS_GETTIMEOFDAY
 #include <sys/time.h>
 #endif
@@ -54,6 +55,9 @@
 #else
 #include <sys/dir.h>
 #endif
+#ifdef HAS_LIBGEN_H
+#include <libgen.h>
+#endif
 #ifdef __APPLE__
 #include <mach-o/dyld.h>
 #endif
@@ -541,3 +545,76 @@ void caml_plat_mem_unmap(void* mem, uintnat size)
   if (munmap(mem, size) != 0)
     CAMLassert(0);
 }
+
+static char * caml_dirname (const char * path)
+{
+#ifdef HAS_LIBGEN_H
+  char *dir, *res;
+  dir = caml_stat_strdup(path);
+  res = caml_stat_strdup(dirname(dir));
+  caml_stat_free(dir);
+  return res;
+#else
+  /* See Filename.generic_dirname */
+  ptrdiff_t n = strlen(path) - 1;
+  char *res;
+  if (n < 0) /* path is "" */
+    return caml_stat_strdup(".");
+  while (n >= 0 && path[n] == '/')
+    n--;
+  if (n < 0) /* path is entirely slashes */
+    return caml_stat_strdup("/");
+  while (n >= 0 && path[n] != '/')
+    n--;
+  if (n < 0) /* path is relative */
+    return caml_stat_strdup(".");
+  while (n >= 0 && path[n] == '/')
+    n--;
+  if (n < 0) /* path is a file at root */
+    return caml_stat_strdup("/");
+  /* n is the _index_ of the last character of the dirname */
+  res = caml_stat_alloc(n + 2);
+  memcpy(res, path, n + 1);
+  res[n + 1] = 0;
+  return res;
+#endif
+}
+
+#define Is_relative_dir(dir) \
+  (dir[0] == '.' \
+   && (dir[1] == '\0' \
+       || dir[1] == '/' \
+       || (dir[1] == '.' && (dir[2] == '\0' || dir[2] == '/'))))
+
+CAMLextern char_os* caml_locate_standard_library (const char *exe_name,
+                                                  const char *stdlib_default,
+                                                  char **dirname)
+{
+  if (Is_relative_dir(stdlib_default)) {
+    char * root = caml_dirname(exe_name);
+    char * candidate =
+      caml_stat_strconcat(3, root, "/", stdlib_default);
+    /* In practice, a system which can be configured --with-relative-libdir will
+       also have realpath. The directory is normalised here for consistency with
+       the behaviour on Windows, which doesn't have a direct equivalent of
+       dirname and performs the equivalent of realpath as a side-effect of
+       determining the root path. */
+#ifdef HAS_REALPATH
+    char * resolved_candidate = realpath(candidate, NULL);
+    /* If realpath fails, use the non-normalised path for error messages. */
+    if (resolved_candidate != NULL) {
+      caml_stat_free(candidate);
+      /* realpath uses malloc */
+      candidate = caml_stat_strdup(resolved_candidate);
+      free(resolved_candidate);
+    }
+#endif
+    if (dirname == NULL)
+      caml_stat_free(root);
+    else
+      *dirname = root;
+    return candidate;
+  } else {
+    return caml_stat_strdup(stdlib_default);
+  }
+}
diff --git a/runtime/win32.c b/runtime/win32.c
index 3ec659d42ad9..5df267790339 100644
--- a/runtime/win32.c
+++ b/runtime/win32.c
@@ -41,6 +41,7 @@
 #include <errno.h>
 #include <string.h>
 #include <signal.h>
+#include <wchar.h>
 #include "caml/alloc.h"
 #include "caml/codefrag.h"
 #include "caml/fail.h"
@@ -1272,3 +1273,96 @@ value caml_win32_xdg_defaults(void)
 
   CAMLreturn(result);
 }
+
+#define Is_separator(c) (c == '\\' || c == '/')
+
+#define Is_relative_dir(dir) \
+  (dir[0] == '.' \
+   && (dir[1] == '\0' \
+       || Is_separator(dir[1]) \
+       || (dir[1] == '.' && (dir[2] == '\0' || Is_separator(dir[2])))))
+
+CAMLextern char_os* caml_locate_standard_library (const wchar_t *exe_name,
+                                                  const wchar_t *stdlib_default,
+                                                  wchar_t **dirname)
+{
+  if (Is_relative_dir(stdlib_default)) {
+    LPWSTR root = NULL, basename;
+    DWORD l = MAX_PATH + 1, buf_len;
+
+    do {
+      buf_len = l;
+      caml_stat_free(root);
+      root = caml_stat_alloc(buf_len * sizeof(WCHAR));
+      l = GetFullPathName(exe_name, buf_len, root, &basename);
+    } while (l >= buf_len);
+    /* It should be an Impossible Thing for exe_name (which will have been the
+       result of GetModuleFileName) to be unparsable by GetFullPathName */
+    if (l == 0) {
+      caml_stat_free(root);
+      return caml_stat_wcsdup(stdlib_default);
+    }
+
+    CAMLassert(basename && basename != root && Is_separator(*(basename - 1)));
+
+    /* Make root the dirname portion */
+    *(basename - 1) = 0;
+
+    LPWSTR candidate =
+      caml_stat_wcsconcat(3, root, T("\\"), stdlib_default);
+    HANDLE h =
+      CreateFile(candidate, 0,
+                 FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+                 OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+    if (h == INVALID_HANDLE_VALUE) {
+      caml_stat_free(candidate);
+      return caml_stat_wcsdup(stdlib_default);
+    }
+
+    LPWSTR resolved_candidate = NULL;
+    l = MAX_PATH + 1;
+    do {
+      buf_len = l;
+      caml_stat_free(resolved_candidate);
+      resolved_candidate = caml_stat_alloc(buf_len * sizeof(WCHAR));
+      l = GetFinalPathNameByHandle(h, resolved_candidate, buf_len,
+                                   FILE_NAME_NORMALIZED | VOLUME_NAME_DOS);
+    } while (l >= buf_len);
+
+    if (l > 0) {
+      /* GetFinalPathNameByHandle always returns \\?\ which needs stripping. */
+      CAMLassert(l > 4 && resolved_candidate[0] == '\\'
+                       && resolved_candidate[1] == '\\'
+                       && resolved_candidate[2] == '?'
+                       && resolved_candidate[3] == '\\');
+
+      caml_stat_free(candidate);
+
+      if (l >= 8 && resolved_candidate[4] == 'U'
+                 && resolved_candidate[5] == 'N'
+                 && resolved_candidate[6] == 'C'
+                 && resolved_candidate[7] == '\\') {
+        /* NT native UNC path (\\?\UNC\foo). We change the last C to a backslash
+           (\\?\UN\\foo) and then include that altered character and the
+           original final slash to create a normal UNC path. */
+        resolved_candidate[6] = '\\';
+        candidate = caml_stat_wcsdup(resolved_candidate + 6);
+      } else {
+        /* Local device path */
+        candidate = caml_stat_wcsdup(resolved_candidate + 4);
+      }
+    }
+
+    /* It should be another Impossible Thing for l == 0 in the above. If that
+       did happen, candidate will _not_ have been freed, and we'll return the
+       path returned by GetFullPathName */
+    caml_stat_free(resolved_candidate);
+
+    if (dirname != NULL)
+      *dirname = caml_stat_wcsdup(root);
+    caml_stat_free(root);
+    return candidate;
+  } else {
+    return caml_stat_wcsdup(stdlib_default);
+  }
+}
diff --git a/stdlib/Makefile b/stdlib/Makefile
index a7f2e60a7aa0..fcd82f18e157 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -14,6 +14,7 @@
 #**************************************************************************
 
 ROOTDIR = ..
+SUBDIR_NAME = stdlib
 # NOTE: it is important that the OCAMLDEP variable is defined *before*
 # Makefile.common gets included, so that its local definition here
 # take precedence over its general shared definitions in Makefile.common.
@@ -47,6 +48,9 @@ endif
 OPTCOMPILER=$(ROOTDIR)/ocamlopt$(EXE)
 CAMLOPT=$(OCAMLRUN) $(OPTCOMPILER)
 
+# At present, only META is installed to the package directory
+LIBNAME = stdlib
+
 include StdlibModules
 
 OBJS=$(addsuffix .cmo,$(STDLIB_MODULES))
@@ -54,49 +58,72 @@ NOSTDLIB= camlinternalFormatBasics.cmo stdlib.cmo
 OTHERS=$(filter-out $(NOSTDLIB),$(OBJS))
 
 .PHONY: all
-all: stdlib.cma std_exit.cmo $(HEADER_NAME) target_$(HEADER_NAME)
+all: stdlib.cma std_exit.cmo $(HEADER_NAME)
 
 .PHONY: allopt opt.opt # allopt and opt.opt are synonyms
 allopt: stdlib.cmxa std_exit.cmx
 opt.opt: allopt
 
-INSTALL_STDLIB_META_DIR=$(DESTDIR)$(LIBDIR)/stdlib
-
 .PHONY: install
 install::
-	$(INSTALL_DATA) \
-	  stdlib.cma std_exit.cmo *.cmi "$(INSTALL_LIBDIR)"
-	$(MKDIR) "$(INSTALL_STDLIB_META_DIR)"
-	$(INSTALL_DATA) META "$(INSTALL_STDLIB_META_DIR)"
+	$(call INSTALL_ITEMS, stdlib.cma std_exit.cmo *.cmi, lib)
+	$(call INSTALL_ITEMS, META, lib, $(LIBNAME))
 ifeq "$(INSTALL_SOURCE_ARTIFACTS)" "true"
-	$(INSTALL_DATA) \
-	  *.cmt *.cmti *.mli *.ml *.ml.in \
-	  "$(INSTALL_LIBDIR)"
+	$(call INSTALL_ITEMS, *.cmt *.cmti *.mli *.ml *.ml.in, lib)
 endif
-	$(INSTALL_DATA) target_$(HEADER_NAME) "$(INSTALL_LIBDIR)/$(HEADER_NAME)"
+	$(call INSTALL_ITEMS, $(HEADER_NAME), lib)
 
 .PHONY: installopt
 installopt: installopt-default
 
 .PHONY: installopt-default
 installopt-default:
-	$(INSTALL_DATA) \
-	  stdlib.cmxa stdlib.$(A) std_exit.$(O) *.cmx \
-	  "$(INSTALL_LIBDIR)"
-
-ifeq "$(UNIX_OR_WIN32)" "unix"
-HEADERPROGRAM = header
-else # Windows
-HEADERPROGRAM = headernt
+	$(call INSTALL_ITEMS, stdlib.cmxa stdlib.$(A) std_exit.$(O) *.cmx, lib)
+
+MANGLING = $(filter true,$(SUFFIXING))
+runtime-launch-info: tmpheader.exe
+	@{ printf '$(if $(MANGLING),$(ZINC_RUNTIME_ID),\000)'; \
+	   cat $^; } > $@
+
+# The mingw-w64 and MSVC versions of tmpheader.exe are linked with special flags
+# to reduce their size (considerably). In particular, the entry point is
+# overridden, which prevents the linking of crt0.
+ifeq "$(TOOLCHAIN)" "mingw"
+# mingw-w64: optimise header.o for space and remove all unused sections during
+# linking.
+header.o: OC_CFLAGS += -Os
+ifeq "$(SYSTEM)" "mingw"
+  ENTRYPOINT = _wmainCRTStartup
+else
+  ENTRYPOINT = wmainCRTStartup
+endif
+# Certainly for GCC, -nostdlib automatically adds -nostartfiles (clang's
+# documentation is not explicit on this point, but it would be unusual for clang
+# and GCC to differ). --gc-sections removes unreferenced code and data sections.
+tmpheader.exe: OC_LDFLAGS += \
+  -nostdlib -nostartfiles -Wl,--gc-sections -Wl,-e,$(ENTRYPOINT)
+HEADERLIBS = -lkernel32
+else ifeq "$(TOOLCHAIN)" "msvc"
+# MSVC: Optimise header.obj for space. cl doesn't have an equivalent of
+# -nostdlib, however it also doesn't have default libraries in the same way as
+# GCC - the equivalent of crt0.o is linked because it provides the entry point
+# symbol, rather than by being explicitly added to the linking command line.
+# /GS- disables compilation of runtime security checks and /NOCOFFGRPINFO is an
+# undocumented linker flag which removes the debug directory from the PE+ image.
+header.obj: OC_CFLAGS += /GS- /Os
+tmpheader.exe: OC_LDFLAGS += /NOCOFFGRPINFO /subsystem:console
+HEADERLIBS = kernel32.lib
+else
+HEADERLIBS =
 endif
-
-%-launch-info: %.info tmpheader.exe
-	@cat $^ >> $@
 
 .INTERMEDIATE: tmpheader.exe
-tmpheader.exe: $(HEADERPROGRAM).$(O)
-	$(V_MKEXE)$(call MKEXE_VIA_CC,$@,$^)
+tmpheader.exe: header.$(O)
+	$(V_MKEXE)$(call MKEXE_VIA_CC,$@,$^ $(HEADERLIBS))
+# Do not strip the header produced by cl
+ifneq "$(TOOLCHAIN)" "msvc"
 	$(STRIP) $@
+endif
 
 stdlib.cma: $(OBJS)
 	$(V_LINKC)$(CAMLC) -a -o $@ $^
@@ -106,11 +133,11 @@ stdlib.cmxa: $(OBJS:.cmo=.cmx)
 
 .PHONY: distclean
 distclean: clean
-	rm -f sys.ml META runtime.info target_runtime.info
+	rm -f sys.ml META
 
 .PHONY: clean
 clean::
-	rm -f $(HEADER_NAME) target_$(HEADER_NAME)
+	rm -f $(HEADER_NAME)
 
 export AWK
 
diff --git a/stdlib/header.c b/stdlib/header.c
index 164bf9de2f56..c194105034ee 100644
--- a/stdlib/header.c
+++ b/stdlib/header.c
@@ -13,33 +13,172 @@
 /*                                                                        */
 /**************************************************************************/
 
-#define CAML_INTERNALS
+/* The launcher for bytecode executables (if #! is not available) */
+
+/* C11's _Noreturn is deprecated in C23 in favour of attributes */
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
+  #define NORETURN [[noreturn]]
+#else
+  #define NORETURN _Noreturn
+#endif
+
+#include <errno.h>
+
+#ifdef _WIN32
+
+#define STRICT
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+typedef wchar_t char_os;
+typedef wchar_t * argv_t;
+#define T(x) L ## x
+#define Is_separator(c) (c == '\\' || c == '/')
+#define Directory_separator_character T('\\')
+#define ITOL(i) L ## #i
+#define ITOT(i) ITOL(i)
+#define PATH_NAME L"%Path%"
+
+#if WINDOWS_UNICODE
+#define CP CP_UTF8
+/* The characters in RNTM will be converted from UTF-8 to UTF-16. Parasitically,
+   there could be 4 bytes in RNTM for every wchar_t in the actual value. */
+#define RNTM_ENCODING_LENGTH 4
+#else
+#define CP CP_ACP
+#endif
+
+/* mingw-w64 has a limits.h which defines PATH_MAX as an alias for MAX_PATH */
+#if !defined(PATH_MAX)
+#define PATH_MAX MAX_PATH
+#endif
+
+#define SEEK_END FILE_END
+
+#define lseek(h, offset, origin) SetFilePointer((h), (offset), NULL, (origin))
+
+typedef HANDLE file_descriptor;
+
+#define unsafe_copy(dst, src, dstsize) lstrcpy(dst, src)
+
+static int read(HANDLE h, LPVOID buffer, DWORD buffer_size)
+{
+  DWORD nread = 0;
+  ReadFile(h, buffer, buffer_size, &nread, NULL);
+  return nread;
+}
+
+static BOOL WINAPI ctrl_handler(DWORD event)
+{
+  if (event == CTRL_C_EVENT || event == CTRL_BREAK_EVENT)
+    return TRUE;                /* pretend we've handled them */
+  else
+    return FALSE;
+}
+
+static int exec_file(wchar_t *file, wchar_t *cmdline)
+{
+  wchar_t truename[MAX_PATH];
+  STARTUPINFO stinfo;
+  PROCESS_INFORMATION procinfo;
+  DWORD retcode;
 
-/* The launcher for bytecode executables (if #! is not working) */
+  if (SearchPath(NULL, file, L".exe", sizeof(truename)/sizeof(wchar_t),
+                 truename, NULL)) {
+    /* Need to ignore ctrl-C and ctrl-break, otherwise we'll die and take the
+       underlying OCaml program with us! */
+    SetConsoleCtrlHandler(ctrl_handler, TRUE);
+
+    stinfo.cb = sizeof(stinfo);
+    stinfo.lpReserved = NULL;
+    stinfo.lpDesktop = NULL;
+    stinfo.lpTitle = NULL;
+    stinfo.dwFlags = 0;
+    stinfo.cbReserved2 = 0;
+    stinfo.lpReserved2 = NULL;
+    if (CreateProcess(truename, cmdline, NULL, NULL, TRUE, 0, NULL, NULL,
+                      &stinfo, &procinfo)) {
+      CloseHandle(procinfo.hThread);
+      WaitForSingleObject(procinfo.hProcess, INFINITE);
+      GetExitCodeProcess(procinfo.hProcess, &retcode);
+      CloseHandle(procinfo.hProcess);
+      ExitProcess(retcode);
+    } else {
+      return ENOEXEC;
+    }
+  } else {
+    return ENOENT;
+  }
+}
+
+static void write_error(const wchar_t *wstr, HANDLE hOut)
+{
+  DWORD consoleMode, numwritten, len;
+  char str[MAX_PATH];
+
+  if (GetConsoleMode(hOut, &consoleMode) != 0) {
+    /* The output stream is a Console */
+    WriteConsole(hOut, wstr, lstrlen(wstr), &numwritten, NULL);
+  } else { /* The output stream is redirected */
+    len =
+      WideCharToMultiByte(CP, 0, wstr, lstrlen(wstr), str, sizeof(str),
+                          NULL, NULL);
+    WriteFile(hOut, str, len, &numwritten, NULL);
+  }
+}
+
+NORETURN static void exit_with_error(const wchar_t *wstr1,
+                                     const wchar_t *wstr2,
+                                     const wchar_t *wstr3)
+{
+  HANDLE hOut = GetStdHandle(STD_ERROR_HANDLE);
+  if (wstr1) write_error(wstr1, hOut);
+  if (wstr2) write_error(wstr2, hOut);
+  if (wstr3) write_error(wstr3, hOut);
+  write_error(L"\r\n", hOut);
+  ExitProcess(2);
+}
+
+#else
+
+#include "caml/s.h"
+#include "sys_int.h"
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include "caml/s.h"
-#ifdef HAS_UNISTD
 #include <unistd.h>
-#endif
 #include <fcntl.h>
+#include <limits.h>
+#ifdef HAS_LIBGEN_H
+#include <libgen.h>
+#endif
 #include <sys/types.h>
 #include <sys/stat.h>
-#include "caml/mlvalues.h"
-#include "caml/exec.h"
 
-#ifndef MAXPATHLEN
-#define MAXPATHLEN 1024
+/* O_BINARY is defined in Gnulib, but is not POSIX */
+#ifndef O_BINARY
+#define O_BINARY 0
 #endif
 
-#ifndef S_ISREG
-#define S_ISREG(mode) (((mode) & S_IFMT) == S_IFREG)
-#endif
+typedef int file_descriptor;
+
+typedef char char_os;
+typedef char ** argv_t;
+#define T(x) x
+#define Is_separator(c) (c == '/')
+#define Directory_separator_character '/'
+#define ITOL(x) #x
+#define ITOT(x) ITOL(x)
+#define PATH_NAME "$PATH"
 
-#ifndef SEEK_END
-#define SEEK_END 2
+#ifdef HAS_STRLCPY
+/* The macro is named unsafe_copy because although it requires a dstsize
+   argument which _may_ be passed to strlcpy, there are platforms where the
+   underlying operation is unsafe and will ignore dstsize. */
+#define unsafe_copy strlcpy
+#else
+#define unsafe_copy(dst, src, dstsize) strcpy(dst, src)
 #endif
 
 #ifndef __CYGWIN__
@@ -48,7 +187,7 @@
 
 static char * searchpath(char * name)
 {
-  static char fullname[MAXPATHLEN + 1];
+  static char fullname[PATH_MAX + 1];
   char * path;
   struct stat st;
 
@@ -60,11 +199,11 @@ static char * searchpath(char * name)
   while(1) {
     char * p;
     for (p = fullname; *path != 0 && *path != ':'; p++, path++)
-      if (p < fullname + MAXPATHLEN) *p = *path;
-    if (p != fullname && p < fullname + MAXPATHLEN)
+      if (p < fullname + PATH_MAX) *p = *path;
+    if (p != fullname && p < fullname + PATH_MAX)
       *p++ = '/';
     for (char *q = name; *q != 0; p++, q++)
-      if (p < fullname + MAXPATHLEN) *p = *q;
+      if (p < fullname + PATH_MAX) *p = *q;
     *p = 0;
     if (stat(fullname, &st) == 0 && S_ISREG(st.st_mode)) break;
     if (*path == 0) return name;
@@ -123,68 +262,219 @@ static char * searchpath(char * name)
 
 #endif
 
-static unsigned long read_size(char * ptr)
+NORETURN static void exit_with_error(const char *str1,
+                                     const char *str2,
+                                     const char *str3)
+{
+  if (str1) fputs(str1, stderr);
+  if (str2) fputs(str2, stderr);
+  if (str3) fputs(str3, stderr);
+  fputs("\n", stderr);
+  exit(2);
+}
+
+static int exec_file(const char *file, char * const argv[])
+{
+  return (execvp(file, argv) == -1 ? errno : 0);
+}
+
+#endif /* defined(_WIN32) */
+
+#include "caml/version.h"
+#define SHORT_VERSION ITOT(OCAML_VERSION_MAJOR) T(".") ITOT(OCAML_VERSION_MINOR)
+
+#define CAML_INTERNALS
+#include "caml/exec.h"
+
+static uint32_t read_size(const char *ptr)
 {
-  unsigned char * p = (unsigned char *) ptr;
-  return ((unsigned long) p[0] << 24) + ((unsigned long) p[1] << 16) +
-         ((unsigned long) p[2] << 8) + p[3];
+  const unsigned char *p = (const unsigned char *)ptr;
+  return ((uint32_t) p[0] << 24) | ((uint32_t) p[1] << 16) |
+         ((uint32_t) p[2] << 8) | p[3];
 }
 
-static char * read_runtime_path(int fd)
+#ifndef RNTM_ENCODING_LENGTH
+#define RNTM_ENCODING_LENGTH 1
+#endif
+
+static char * read_runtime_path(file_descriptor fd, uint32_t *rntm_strlen)
 {
   char buffer[TRAILER_SIZE];
-  static char runtime_path[MAXPATHLEN];
+  static char runtime_path[PATH_MAX * RNTM_ENCODING_LENGTH];
   int num_sections;
-  uint32_t path_size;
   long ofs;
 
-  lseek(fd, (long) -TRAILER_SIZE, SEEK_END);
+  if (lseek(fd, -TRAILER_SIZE, SEEK_END) == -1) return NULL;
   if (read(fd, buffer, TRAILER_SIZE) < TRAILER_SIZE) return NULL;
   num_sections = read_size(buffer);
   ofs = TRAILER_SIZE + num_sections * 8;
-  lseek(fd, -ofs, SEEK_END);
-  path_size = 0;
+  if (lseek(fd, -ofs, SEEK_END) == -1) return NULL;
+  *rntm_strlen = 0;
   for (int i = 0; i < num_sections; i++) {
     if (read(fd, buffer, 8) < 8) return NULL;
     if (buffer[0] == 'R' && buffer[1] == 'N' &&
         buffer[2] == 'T' && buffer[3] == 'M') {
-      path_size = read_size(buffer + 4);
-      ofs += path_size;
-    } else if (path_size > 0)
+      *rntm_strlen = read_size(buffer + 4);
+      ofs += *rntm_strlen;
+    } else if (*rntm_strlen > 0)
       ofs += read_size(buffer + 4);
   }
-  if (path_size == 0) return NULL;
-  if (path_size >= MAXPATHLEN) return NULL;
-  lseek(fd, -ofs, SEEK_END);
-  if (read(fd, runtime_path, path_size) != path_size) return NULL;
+  if (*rntm_strlen == 0) return NULL;
+  /* The last character of runtime_path must be '\0', so RNTM must be strictly
+     less than PATH_MAX */
+  if (*rntm_strlen >= PATH_MAX * RNTM_ENCODING_LENGTH) return NULL;
+  if (lseek(fd, -ofs, SEEK_END) == -1) return NULL;
+  if (read(fd, runtime_path, *rntm_strlen) != *rntm_strlen) return NULL;
+
   return runtime_path;
 }
 
-static void errwrite(char * msg)
+/* rntm points to a buffer containing rntm_bsz characters consisting of the
+   decoded content of the RNTM section (which may include NUL characters) and an
+   additional NUL "terminator".
+   RNTM is either <runtime>[\0] or [<runtime-dirname>]\0<runtime-basename>
+   Decode rntm and search for a runtime (using argv0_dirname if non-NULL and
+   required) and exec the first runtime found passing argv. */
+NORETURN void search_and_exec_runtime(char_os *rntm, uint32_t rntm_bsz,
+                                      argv_t argv, char_os *argv0_dirname)
+{
+  /* rntm_end points to the NUL "terminator" of rntm (_not_ the last character
+     of the RNTM section */
+  const char_os *rntm_end = rntm + (rntm_bsz - 1);
+
+  char_os *rntm_bindir_end = rntm;
+
+  /* Scan for the first NUL character in rntm (there is always one) */
+  while (*rntm_bindir_end != 0)
+    rntm_bindir_end++;
+
+  /* The first character of rntm is NUL for Enable mode */
+  if (*rntm != 0) {
+    /* For Disable mode, there is no NUL in RNTM, so rntm_bindir_end points to
+       the terminator pointed to by rntm_end. For Fallback, there is a NUL in
+       the middle of the RNTM "string", which rntm_bindir_end points at. Change
+       that to a directory separator, so that rntm now points to a
+       NUL-terminated full path we can attempt to exec. */
+    if (rntm_bindir_end != rntm_end)
+      *rntm_bindir_end = Directory_separator_character;
+    int status = exec_file(rntm, argv);
+    /* exec failed. For Disable mode, there's nothing else to be tried. For
+       Fallback, if the failure was for any other reason than ENOENT then there
+       is also nothing else to be tried. */
+    if (rntm_bindir_end == rntm_end || status != ENOENT)
+      exit_with_error(T("Cannot exec "), rntm, NULL);
+  }
+
+  /* Shift rntm to point to <runtime-basename> */
+  rntm = rntm_bindir_end + 1;
+  if (rntm < rntm_end) {
+    /* Searching takes place first in the directory containing this executable,
+       if it's known. */
+    if (argv0_dirname != NULL) {
+      char_os root[PATH_MAX];
+      unsafe_copy(root, argv0_dirname, PATH_MAX);
+
+      /* Ensure root ends with a directory separator. root_basename points to
+         the character at which to place <runtime-basename> */
+      char_os *root_basename = root;
+      while (*root_basename != 0)
+        root_basename++;
+      if (root_basename > root && !Is_separator(*(root_basename - 1)))
+        *root_basename++ = Directory_separator_character;
+
+      /* If there isn't enough space to copy rntm to root then simply skip this
+         check (e.g. an executable called b.exe in a very long directory name).
+         (root_basename - root) is strlen_os(root) and likewise
+         (rntm_end - rntm) is strlen_os(rntm). */
+      if ((rntm_end - rntm) <= PATH_MAX - (root_basename - root) - 1) {
+        unsafe_copy(root_basename, rntm, PATH_MAX - (root_basename - root));
+        if (exec_file(root, argv) != ENOENT)
+          exit_with_error(T("Cannot exec "), root, NULL);
+      }
+    }
+
+    /* Otherwise, search in PATH */
+    if (exec_file(rntm, argv) != ENOENT)
+      exit_with_error(T("Cannot exec "), rntm, NULL);
+  }
+
+  /* If we get here, we've failed... */
+  exit_with_error(T("This program requires OCaml ") SHORT_VERSION T("\n")
+                  T("Interpreter ("), (rntm_bindir_end + 1),
+                  T(") not found alongside the program or in " PATH_NAME));
+}
+
+#ifdef _WIN32
+
+NORETURN void __cdecl wmainCRTStartup(void)
 {
-  fputs(msg, stderr);
+  wchar_t module[MAX_PATH];
+  wchar_t truename[MAX_PATH];
+  uint32_t rntm_strlen = 0, rntm_bsz = 0;
+  char *runtime_path;
+  wchar_t wruntime_path[MAX_PATH], *dirname;
+  HANDLE h;
+
+  if (GetModuleFileName(NULL, module, sizeof(module)/sizeof(wchar_t)) == 0)
+    exit_with_error(L"Out of memory", NULL, NULL);
+
+  h = CreateFile(module, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE,
+                 NULL, OPEN_EXISTING, 0, NULL);
+
+
+  /* read_runtime_path returns the actual size of RNTM, but the buffer returned
+     is guaranteed to have a null character following the final character of
+     RNTM. */
+  if (h == INVALID_HANDLE_VALUE
+      || (runtime_path = read_runtime_path(h, &rntm_strlen)) == NULL
+      || (rntm_bsz =
+            MultiByteToWideChar(CP, 0, runtime_path, rntm_strlen + 1,
+                                wruntime_path,
+                                sizeof(wruntime_path)/sizeof(wchar_t))) == 0
+      || GetFullPathName(module, sizeof(truename)/sizeof(wchar_t), truename,
+                         &dirname) >= sizeof(truename)/sizeof(wchar_t))
+    exit_with_error(NULL, truename,
+                    L" not found or is not a bytecode executable file");
+  CloseHandle(h);
+
+  if (dirname) {
+    /* GetFullPathName leaves dirname pointing to the first character of the
+       basename, so setting that to NUL means the string pointed to by truename
+       is the dirname of the currently running executable with a trailing
+       separator (although search_and_exec_runtime will check that anyway) */
+    *dirname = 0;
+    dirname = truename;
+  }
+
+  search_and_exec_runtime(wruntime_path, rntm_bsz, GetCommandLine(), dirname);
 }
 
-#ifndef O_BINARY
-#define O_BINARY 0
-#endif
+#else
 
-int main(int argc, char ** argv)
+int main(int argc, char *argv[])
 {
-  char * truename, * runtime_path;
+  char *truename, *runtime_path, *argv0_dirname;
+  uint32_t rntm_strlen = 0;
   int fd;
 
   truename = searchpath(argv[0]);
   fd = open(truename, O_RDONLY | O_BINARY);
-  if (fd == -1 || (runtime_path = read_runtime_path(fd)) == NULL) {
-    errwrite(truename);
-    errwrite(" not found or is not a bytecode executable file\n");
-    return 2;
-  }
+  if (fd == -1 || (runtime_path = read_runtime_path(fd, &rntm_strlen)) == NULL)
+    exit_with_error(NULL, truename,
+                    " not found or is not a bytecode executable file");
+  close(fd);
+
+#ifdef HAS_LIBGEN_H
+  argv0_dirname = dirname(strdup(truename));
+#else
+  argv0_dirname = NULL;
+#endif
+
   argv[0] = truename;
-  execv(runtime_path, argv);
-  errwrite("Cannot exec ");
-  errwrite(runtime_path);
-  errwrite("\n");
-  return 2;
+  /* read_runtime_path returns the actual size of RNTM, but the buffer returned
+     is guaranteed to have a null character following the final character of
+     RNTM. */
+  search_and_exec_runtime(runtime_path, rntm_strlen + 1, argv, argv0_dirname);
 }
+
+#endif /* defined(_WIN32) */
diff --git a/stdlib/headernt.c b/stdlib/headernt.c
deleted file mode 100644
index 9815f0415b51..000000000000
--- a/stdlib/headernt.c
+++ /dev/null
@@ -1,169 +0,0 @@
-/**************************************************************************/
-/*                                                                        */
-/*                                 OCaml                                  */
-/*                                                                        */
-/*             Xavier Leroy, projet Cristal, INRIA Rocquencourt           */
-/*                                                                        */
-/*   Copyright 1998 Institut National de Recherche en Informatique et     */
-/*     en Automatique.                                                    */
-/*                                                                        */
-/*   All rights reserved.  This file is distributed under the terms of    */
-/*   the GNU Lesser General Public License version 2.1, with the          */
-/*   special exception on linking described in the file LICENSE.          */
-/*                                                                        */
-/**************************************************************************/
-
-#define CAML_INTERNALS
-
-#define STRICT
-#define WIN32_LEAN_AND_MEAN
-
-#include <windows.h>
-#include "caml/mlvalues.h"
-#include "caml/exec.h"
-
-#ifndef __MINGW32__
-#pragma comment(linker , "/subsystem:console")
-#pragma comment(lib , "kernel32")
-#ifdef _UCRT
-#pragma comment(lib , "ucrt.lib")
-#pragma comment(lib , "vcruntime.lib")
-#endif
-#endif
-
-Caml_inline unsigned long read_size(const char * const ptr)
-{
-  const unsigned char * const p = (const unsigned char * const) ptr;
-  return ((unsigned long) p[0] << 24) | ((unsigned long) p[1] << 16) |
-         ((unsigned long) p[2] << 8) | p[3];
-}
-
-Caml_inline char * read_runtime_path(HANDLE h)
-{
-  char buffer[TRAILER_SIZE];
-  static char runtime_path[MAX_PATH];
-  DWORD nread;
-  int num_sections, path_size;
-  long ofs;
-
-  if (SetFilePointer(h, -TRAILER_SIZE, NULL, FILE_END) == -1) return NULL;
-  if (! ReadFile(h, buffer, TRAILER_SIZE, &nread, NULL)) return NULL;
-  if (nread != TRAILER_SIZE) return NULL;
-  num_sections = read_size(buffer);
-  ofs = TRAILER_SIZE + num_sections * 8;
-  if (SetFilePointer(h, - ofs, NULL, FILE_END) == -1) return NULL;
-  path_size = 0;
-  for (int i = 0; i < num_sections; i++) {
-    if (! ReadFile(h, buffer, 8, &nread, NULL) || nread != 8) return NULL;
-    if (buffer[0] == 'R' && buffer[1] == 'N' &&
-        buffer[2] == 'T' && buffer[3] == 'M') {
-      path_size = read_size(buffer + 4);
-      ofs += path_size;
-    } else if (path_size > 0)
-      ofs += read_size(buffer + 4);
-  }
-  if (path_size == 0) return NULL;
-  if (path_size >= MAX_PATH) return NULL;
-  if (SetFilePointer(h, -ofs, NULL, FILE_END) == -1) return NULL;
-  if (! ReadFile(h, runtime_path, path_size, &nread, NULL)) return NULL;
-  if (nread != path_size) return NULL;
-  return runtime_path;
-}
-
-static BOOL WINAPI ctrl_handler(DWORD event)
-{
-  if (event == CTRL_C_EVENT || event == CTRL_BREAK_EVENT)
-    return TRUE;                /* pretend we've handled them */
-  else
-    return FALSE;
-}
-
-#if WINDOWS_UNICODE
-#define CP CP_UTF8
-#else
-#define CP CP_ACP
-#endif
-
-static void write_console(HANDLE hOut, WCHAR *wstr)
-{
-  DWORD consoleMode, numwritten, len;
-  static char str[MAX_PATH];
-
-  if (GetConsoleMode(hOut, &consoleMode) != 0) {
-    /* The output stream is a Console */
-    WriteConsole(hOut, wstr, wcslen(wstr), &numwritten, NULL);
-  } else { /* The output stream is redirected */
-    len =
-      WideCharToMultiByte(CP, 0, wstr, wcslen(wstr), str, sizeof(str),
-                          NULL, NULL);
-    WriteFile(hOut, str, len, &numwritten, NULL);
-  }
-}
-
-CAMLnoret Caml_inline void run_runtime(wchar_t * runtime,
-         wchar_t * const cmdline)
-{
-  wchar_t path[MAX_PATH];
-  STARTUPINFO stinfo;
-  PROCESS_INFORMATION procinfo;
-  DWORD retcode;
-  if (SearchPath(NULL, runtime, L".exe", sizeof(path)/sizeof(wchar_t),
-                 path, NULL) == 0) {
-    HANDLE errh;
-    errh = GetStdHandle(STD_ERROR_HANDLE);
-    write_console(errh, L"Cannot exec ");
-    write_console(errh, runtime);
-    write_console(errh, L"\r\n");
-    ExitProcess(2);
-  }
-  /* Need to ignore ctrl-C and ctrl-break, otherwise we'll die and take
-     the underlying OCaml program with us! */
-  SetConsoleCtrlHandler(ctrl_handler, TRUE);
-
-  stinfo.cb = sizeof(stinfo);
-  stinfo.lpReserved = NULL;
-  stinfo.lpDesktop = NULL;
-  stinfo.lpTitle = NULL;
-  stinfo.dwFlags = 0;
-  stinfo.cbReserved2 = 0;
-  stinfo.lpReserved2 = NULL;
-  if (!CreateProcess(path, cmdline, NULL, NULL, TRUE, 0, NULL, NULL,
-                     &stinfo, &procinfo)) {
-    HANDLE errh;
-    errh = GetStdHandle(STD_ERROR_HANDLE);
-    write_console(errh, L"Cannot exec ");
-    write_console(errh, runtime);
-    write_console(errh, L"\r\n");
-    ExitProcess(2);
-  }
-  CloseHandle(procinfo.hThread);
-  WaitForSingleObject(procinfo.hProcess , INFINITE);
-  GetExitCodeProcess(procinfo.hProcess , &retcode);
-  CloseHandle(procinfo.hProcess);
-  ExitProcess(retcode);
-}
-
-int wmain(void)
-{
-  wchar_t truename[MAX_PATH];
-  wchar_t * cmdline = GetCommandLine();
-  char * runtime_path;
-  wchar_t wruntime_path[MAX_PATH];
-  HANDLE h;
-
-  GetModuleFileName(NULL, truename, sizeof(truename)/sizeof(wchar_t));
-  h = CreateFile(truename, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE,
-                 NULL, OPEN_EXISTING, 0, NULL);
-  if (h == INVALID_HANDLE_VALUE ||
-      (runtime_path = read_runtime_path(h)) == NULL) {
-    HANDLE errh;
-    errh = GetStdHandle(STD_ERROR_HANDLE);
-    write_console(errh, truename);
-    write_console(errh, L" not found or is not a bytecode executable file\r\n");
-    ExitProcess(2);
-  }
-  CloseHandle(h);
-  MultiByteToWideChar(CP, 0, runtime_path, -1, wruntime_path,
-                      sizeof(wruntime_path)/sizeof(wchar_t));
-  run_runtime(wruntime_path , cmdline);
-}
diff --git a/testsuite/Makefile b/testsuite/Makefile
index 4cad7738954a..a8302c6922dc 100644
--- a/testsuite/Makefile
+++ b/testsuite/Makefile
@@ -166,7 +166,7 @@ all:
 	@$(MAKE) --no-print-directory report
 
 .PHONY: new-without-report
-new-without-report:
+new-without-report: | tests
 	@rm -f $(failstamp)
 	@($(ocamltest) -find-test-dirs tests | while $(IFS_LINE) read -r dir; do \
 	  echo Running tests from \'$$dir\' ... ; \
@@ -185,7 +185,7 @@ check-failstamp:
 	fi
 
 .PHONY: all-%
-all-%:
+all-%: | tests
 	@for dir in tests/$**; do \
 	  $(MAKE) --no-print-directory exec-one DIR=$$dir; \
 	done 2>&1 | tee $(TESTLOG)
@@ -223,7 +223,7 @@ all-%:
 J_ARGUMENT = $(filter-out -j,$(filter -j%,$(MAKEFLAGS)))
 
 .PHONY: parallel-%
-parallel-%:
+parallel-%: | tests
 	@echo | parallel >/dev/null 2>/dev/null \
 	 || (echo "Unable to run the GNU parallel tool;";\
 	     echo "You should install it before using the parallel* targets.";\
@@ -327,3 +327,25 @@ distclean: clean
 report:
 	@if [ ! -f $(TESTLOG) ]; then echo "No $(TESTLOG) file."; exit 1; fi
 	@$(AWK) -f ./summarize.awk < $(TESTLOG)
+
+# When an archive is created by git-archive, this is expanded to the SHA of the
+# commit. The filter-out causes this to be blank if it's run when the Format
+# tag has not been expanded
+GIT_ARCHIVE_SHA = $(filter-out ormat%, $Format:%H$ )
+
+tests:
+	@echo "There are no tests in the tests directory!"
+	@echo "This happens when the sources of OCaml are extracted from a \
+tarball"
+	@echo "generated by git-archive (which includes those generated by \
+GitHub)"
+	@head -n 1 $(ROOTDIR)/VERSION | grep -Fq + || \
+   echo "Note that the release tarballs published at \
+https://caml.inria.fr/pub/distrib/ include all the manual and testsuite sources"
+	@$(if $(GIT_ARCHIVE_SHA),,false)
+	@echo "The required files are in commit $(GIT_ARCHIVE_SHA), for \
+example:"
+	@echo "  git clone https://github.com/ocaml/ocaml \
+--revision $(GIT_ARCHIVE_SHA) --depth 1 git-sources"
+	@echo "  mv git-sources/$@ ."
+	@false
diff --git a/testsuite/in_prefix/Makefile.test b/testsuite/in_prefix/Makefile.test
index cf8d2039c77b..7c968f8a93d8 100644
--- a/testsuite/in_prefix/Makefile.test
+++ b/testsuite/in_prefix/Makefile.test
@@ -23,10 +23,11 @@ DRIVER = ../tools/test_in_prefix$(EXE)
 endif
 
 DRIVER_ARGS = \
-  $(VERBOSE_FLAG) --bindir "$(BINDIR)" --libdir "$(LIBDIR)" \
+  $(VERBOSE_FLAG) --bindir "$(BINDIR)" --libdir '$(TARGET_LIBDIR)' \
   $(call bool_to_with, shebangscripts, $(SHEBANGSCRIPTS)) \
   $(call bool_to_with, ocamlnat, $(INSTALL_OCAMLNAT)) \
   $(call bool_to_with, ocamlopt, $(NATIVE_COMPILER)) \
+  $(RUNTIME_SEARCH_FLAG) \
   $(OTHERLIBRARIES) --pwd "$(SRCDIR_ABS)/testsuite/in_prefix"
 
 default: $(DRIVER)
@@ -39,8 +40,30 @@ else
 VERBOSE_FLAG =
 endif
 
-test-in-prefix: $(DRIVER) ../tools/main_in_c.$(O) ../tools/dump_load_path$(EXE)
+# Generates --without-$(1) if $(2) is empty or --with-$(1)=$(2) otherwise
+RUNTIME_SEARCH_FLAG = \
+  $(if $(RUNTIME_SEARCH),$\
+    --with-runtime-search=$(RUNTIME_SEARCH),$\
+    --without-runtime-search)
+
+export PATH := $(SRCDIR_ABS)/testsuite/in_prefix/poisoned-runtime:$(PATH)
+
+ifeq "$(SUFFIXING)" "true"
+RUNTIME_NAME = ocamlrun-$(ZINC_RUNTIME_ID)$(EXE)
+else
+RUNTIME_NAME = ocamlrun$(EXE)
+endif
+
+test-in-prefix: $(DRIVER) ../tools/main_in_c.$(O) \
+                ../tools/dump_load_path$(EXE) ../tools/poisonedruntime$(EXE)
+	@rm -f ocamlrun*
+	@$(LN) $(ROOTDIR)/runtime/ocamlrun$(EXE) test-$(RUNTIME_NAME)
+	@$(MKDIR) poisoned-runtime
+	@cd poisoned-runtime \
+	  && $(LN) ../../tools/poisonedruntime$(EXE) $(RUNTIME_NAME)
 	@$< $(DRIVER_ARGS)
+	@rm -rf poisoned-runtime
+	@rm -f test-ocamlrun*
 
 SCRUB_ENV = \
   CAML_LD_LIBRARY_PATH OCAMLLIB CAMLLIB OCAMLPARAM OCAMLRUNPARAM CAMLRUNPARAM
diff --git a/testsuite/in_prefix/README.md b/testsuite/in_prefix/README.md
index da889954b1d0..a7a063652a10 100644
--- a/testsuite/in_prefix/README.md
+++ b/testsuite/in_prefix/README.md
@@ -46,7 +46,8 @@ fifth test are re-run and then the entire battery is executed a second time.
 During this second execution, the test harness does whatever is physically
 possible to allow these tests to proceed:
 - Environment variables `CAML_LD_LIBRARY_PATH` and `OCAMLLIB` are manipulated to
-  allow the compiler to operate
+  allow the compiler to operate (unless the compiler has been configured with
+  `--with-relative-libdir`)
 - Bytecode executables which will no longer be able to find `ocamlrun` are
   explicitly passed to `ocamlrun`. The harness always verifies that this step is
   required by first executing the binary and ensuring that it fails and then
@@ -70,11 +71,11 @@ Exercises:
 
 Shims:
 - On Unix, the bytecode toplevel contains the absolute location of `ocamlrun`,
-  so must be explicitly invoked via `ocamlrun`
+  so must be explicitly invoked via `ocamlrun`, unless the compiler is
+  configured with `--enable-runtime-search`
 - Both toplevels contain the absolute location of the Standard Library,
-  requiring `OCAMLLIB` to be set
-- `ld.conf` contains the absolute location of the `stublibs` directory,
-  requiring `CAML_LD_LIBRARY_PATH` to be adjusted
+  requiring `OCAMLLIB` to be set, unless the compiler was configured with
+  `--with-relative-libdir`
 
 ### Loading archives/plugins (.cma / .cmxs) with `Dynlink`
 
@@ -84,14 +85,13 @@ Shims:
 - For a bytecode-only build, `ocamlc` contains the absolute location of
   `ocamlrun`, so must be explicitly invoked via `ocamlrun` (if the native
   compiler is available, then both `ocamlc` and `ocamlopt` will be native
-  executables)
+  executables), unless the compiler is configured with `--enable-runtime-search`
 - Both compilers contain the absolute location of the Standard Library,
-  requiring `OCAMLLIB` to be set
+  requiring `OCAMLLIB` to be set, unless the comnpiler was configured with
+  `--with-relative-libdir`
 - The executable created by `ocamlc` contains the absolute location of
-  `ocamlrun`, so must be both explicitly invoked via `ocamlrun` and also have
-  `CAML_LD_LIBRARY_PATH` adjusted, as that `ocamlrun` will either not load
-  `ld.conf` or (with `OCAMLLIB` set) will be pointed to an `ld.conf` containing
-  the absolute location of the `stublibs` directory
+  `ocamlrun`, so must be explicitly invoked via `ocamlrun`, unless the
+  compiler is configured with `--enable-runtime-search-target`
 
 ### Executing installed bytecode binaries with `-vnum`
 
@@ -101,10 +101,10 @@ program is executed with `-vnum`.
 
 Additionally, for native Windows, executables are additionally called with `-M`
 as an argument, both with and without the `.exe`. This exercises a known bug in
-the hand-off between the executable launcher (`stdlib/headernt.c`) and
-`ocamlrun` where, for example, `ocamlc.byte` when resolved in `PATH` just runs
-as though it were `ocamlrun`. The test works on the basis that `-M` is only a
-valid argument for `ocamlrun` (returning the magic number).
+the hand-off between the executable launcher (`stdlib/header.c`) and `ocamlrun`
+where, for example, `ocamlc.byte` when resolved in `PATH` just runs as though it
+were `ocamlrun`. The test works on the basis that `-M` is only a valid argument
+for `ocamlrun` (returning the magic number).
 
 Exercises:
 - Bytecode executable header and logic in `ocamlc` for computing the "shebang"
@@ -113,7 +113,8 @@ Exercises:
 
 Shims:
 - On builds with shared library support, all the executables will contain the
-  absolute location of `ocamlrun` and will fail to execute
+  absolute location of `ocamlrun` and will fail to execute, unless the compiler
+  was configured with `--enable-runtime-search`
 - On builds without shared library support, executables using libraries with
   C stubs (in particular, `ocamldebug` and `ocamldoc`) are compiled with
   `-custom` and do succeed
@@ -151,6 +152,8 @@ Exercises:
 
 Shims:
 - As with the `Dynlink` test, on bytecode-only builds the compiler must be
-  explicitly invoked via `ocamlrun`
+  explicitly invoked via `ocamlrun`, unless the compiler was configured with
+  `--enable-runtime-search`
 - The executable produced by `ocamlc` by default contains the absolute location
-  of `ocamlrun` and so has to be run explicitly via `ocamlrun`
+  of `ocamlrun` and so has to be run explicitly via `ocamlrun`, unless the
+  compiler was configured with `--enable-runtime-search-target`
diff --git a/testsuite/tests/tool-debugger/find-artifacts/debuggee.ml b/testsuite/tests/tool-debugger/find-artifacts/debuggee.ml
index 37544574d91a..eafe82261272 100644
--- a/testsuite/tests/tool-debugger/find-artifacts/debuggee.ml
+++ b/testsuite/tests/tool-debugger/find-artifacts/debuggee.ml
@@ -1,4 +1,5 @@
 (* TEST
+ unset BUILD_PATH_PREFIX_MAP;
  ocamldebug_script = "${test_source_directory}/input_script";
  debugger;
  shared-libraries;
diff --git a/testsuite/tools/cmdline.ml b/testsuite/tools/cmdline.ml
index 874d259692da..b091f9c83177 100644
--- a/testsuite/tools/cmdline.ml
+++ b/testsuite/tools/cmdline.ml
@@ -104,10 +104,10 @@ let parse argv =
   in
   let config =
     ref {has_ocamlnat = false; has_ocamlopt = false; has_relative_libdir = None;
-         has_runtime_search = None; launcher_searches_for_ocamlrun = false;
+         has_runtime_search = Disable; launcher_searches_for_ocamlrun = false;
          target_launcher_searches_for_ocamlrun = false;
          bytecode_shebangs_by_default = false; shebangscripts = false;
-         libraries = []}
+         filename_mangling = false; libraries = []}
   in
   let error fmt = Printf.ksprintf (fun s -> raise (Arg.Bad s)) fmt in
   let check_tree () =
@@ -163,23 +163,22 @@ let parse argv =
     config := {!config with shebangscripts}
   in
   let parse_search = function
-  | "enable" -> true
-  | "always" -> false
+  | Some "fallback" -> Config.Fallback
+  | Some "enable" -> Config.Enable
+  | None -> Config.Disable
   | _ ->
       raise (Arg.Bad
-        "--with-runtime-search: argument should be either enable or always")
+        "--with-runtime-search: argument should be either fallback or enable")
   in
   let has_runtime_search arg =
-    let has_runtime_search = Option.map parse_search arg in
-    if has_runtime_search <> None then
-      error "--with-runtime-search is not implemented!";
+    let has_runtime_search = parse_search arg in
     config := {!config with has_runtime_search}
   in
   let args = Arg.align [
     "--pwd", Arg.Set_string pwd, "<pwd>\tCurrent working directory to use";
     "--bindir", Arg.String (check_exists ~absolute:true bindir), "\
 <bindir>\tDirectory containing programs (must share a prefix with --libdir)";
-    "--libdir", Arg.String (check_exists ~absolute:true libdir), "\
+    "--libdir", Arg.String (check_exists ~absolute:false libdir), "\
 <libdir>\tDirectory containing stdlib.cma (must share a prefix with --bindir)";
     "--summary", Arg.Set summary, "";
     "--verbose", Arg.Set verbose, "";
diff --git a/testsuite/tools/dump_load_path.c b/testsuite/tools/dump_load_path.c
index 45c70ffc3347..f38a75859b9e 100644
--- a/testsuite/tools/dump_load_path.c
+++ b/testsuite/tools/dump_load_path.c
@@ -22,7 +22,13 @@
 #include <caml/dynlink.h>
 #include <caml/misc.h>
 #include <caml/osdeps.h>
+#include <build_config.h>
 
+extern const char_os *caml_runtime_standard_library_default;
+extern const char_os *caml_runtime_standard_library_effective;
+CAMLextern char_os *caml_locate_standard_library (const char_os *exe_name,
+                                                  const char_os *stdlib_default,
+                                                  char_os **dirname);
 int main_os(int argc, char_os **argv)
 {
   const char_os *dir;
@@ -30,7 +36,11 @@ int main_os(int argc, char_os **argv)
   caml_ext_table_init(&caml_shared_libs_path, 8);
   caml_decompose_path(&caml_shared_libs_path,
                       caml_secure_getenv(T("CAML_LD_LIBRARY_PATH")));
-  caml_parse_ld_conf();
+  caml_runtime_standard_library_effective =
+    caml_locate_standard_library(argv[0],
+                                 caml_runtime_standard_library_default, NULL);
+  caml_parse_ld_conf(caml_runtime_standard_library_effective,
+                     &caml_shared_libs_path);
   for (int i = 0; i < caml_shared_libs_path.size; i++) {
     dir = caml_shared_libs_path.contents[i];
     if (dir[0] == 0)
diff --git a/testsuite/tools/environment.ml b/testsuite/tools/environment.ml
index 8f867887a8ae..108f14860c45 100644
--- a/testsuite/tools/environment.ml
+++ b/testsuite/tools/environment.ml
@@ -46,7 +46,7 @@ let libdir_suffix {libdir_suffix; _} = libdir_suffix
 
 (* Derived properties *)
 
-let is_renamed {phase; _} = (phase = Renamed)
+let is_renamed {phase; _} = (phase <> Original)
 
 let bindir {prefix; bindir_suffix; _} =
   Filename.concat prefix bindir_suffix
@@ -67,19 +67,6 @@ let in_libdir env path =
 let in_test_root {test_root; _} path =
   Filename.concat test_root path
 
-(* Reverse the quoting of single quotes done by Filename.quote on Unix (which is
-   used for the runtime name when embedded in sh-scripts. Any single quote
-   characters are transformed to "'\\''". If the string is split on the single
-   quote characters, the sequence ["\\"; ""] is a single quote character in the
-   unescaped version. *)
-let dequote s =
-  let[@tail_mod_cons] rec loop = function
-  | "\\" :: "" :: rest -> "'" :: loop rest
-  | chunk :: rest -> chunk :: loop rest
-  | [] -> []
-  in
-  String.concat "" (loop (String.split_on_char '\'' s))
-
 (* [classify_executable file] determines if [file] is :
    - Tendered bytecode with an executable header
    - Scripted bytecode invoking ocamlrun with a #! header
@@ -91,49 +78,18 @@ let classify_executable file =
   try
     In_channel.with_open_bin file (fun ic ->
       let start = really_input_string ic 2 in
-      let is_RNTM = function
-      | Bytesections.{name = Name.RNTM; _} -> true
-      | _ -> false
-      in
+      let toc = Bytesections.read_toc ic in
+      let sections = Bytesections.all toc in
       let is_DLLS = function
       | Bytesections.{name = Name.DLLS; len} when len > 0 -> true
       | _ -> false
       in
-      let toc = Bytesections.read_toc ic in
-      let sections = Bytesections.all toc in
-      if start = "#!" then
-        let runtime =
-          seek_in ic 2;
-          let shebang = String.trim (input_line ic) in
-          if Filename.basename shebang = "sh" then
-            let exec_line = input_line ic in
-            if String.starts_with ~prefix:"exec '" exec_line
-               && String.ends_with ~suffix:"' \"$0\" \"$@\"" exec_line then
-              (* When the path to the runtime can't be directly used in a
-                 shebang, the shell is used instead, the next line is then:
-                   exec '<runtime>' "$0" "$@" *)
-              dequote (String.sub exec_line 6 (String.length exec_line - 17))
-            else
-              Harness.fail_because "%s contains an unexpected exec line: %S"
-                                   file exec_line
-          else
-            shebang
-        in
-        Tendered {header = Header_shebang;
-                  dlls = List.exists is_DLLS sections;
-                  runtime}
-      else if List.exists is_RNTM sections then
-        let rntm =
-          Bytesections.read_section_string toc ic Bytesections.Name.RNTM in
-        let len = String.length rntm in
-        if len = 0 || rntm.[len - 1] <> '\000' then
-          Harness.fail_because "%s contains corrupt RNTM: %S" file rntm;
-        let runtime = String.sub rntm 0 (len - 1) in
-        Tendered {header = Header_exe;
-                  dlls = List.exists is_DLLS sections;
-                  runtime}
-      else
-        Custom)
+      let tendered (runtime, id, search) =
+        let header = if start = "#!" then Header_shebang else Header_exe in
+        let dlls = List.exists is_DLLS sections in
+        Tendered {header; dlls; runtime; id; search}
+      in
+      Option.fold ~none:Custom ~some:tendered (Byterntm.read_runtime toc ic))
   with End_of_file | Bytesections.Bad_magic_number ->
     Vanilla
 
@@ -224,7 +180,7 @@ let make pp_path ~verbose ~test_root ~test_root_logical
     let value =
       String.sub binding (equals + 1) (String.length binding - equals - 1)
     in
-    if is_path_env name then
+    if phase <> Execution && is_path_env name then
       if Sys.win32 then
         if String.index_opt bindir ';' <> None then
           Printf.sprintf "%s=\"%s\";%s" name bindir value
@@ -270,7 +226,7 @@ let string_of_process_status = function
    highlighted. If argv0 is specified, then the original program executable is
    also shown. *)
 let display_execution level status pid ~runtime program argv0 args
-                      ({pp_path; verbose; serial; _} as env) =
+                      ({pp_path; verbose; serial; phase; _} as env) =
   let pp_program style program f = function
   | Some argv0 ->
       Format.fprintf f "@{<%s>%s (from %a)@}"
@@ -313,9 +269,11 @@ let display_execution level status pid ~runtime program argv0 args
   if serial <> !last_environment then begin
     last_environment := serial;
     Format.printf "\
-      @{<inline_code>> @}@{<loc>Environment@}\n\
-      @{<inline_code>> @}  @{<loc>PATH=%a:$PATH@}\n"
-      pp_path (bindir env);
+      @{<inline_code>> @}@{<loc>Environment@}\n";
+    if phase <> Execution then
+      Format.printf "\
+        @{<inline_code>> @}  @{<loc>PATH=%a:$PATH@}\n"
+        pp_path (bindir env);
     if not Sys.win32 then
       Format.printf "\
         @{<inline_code>> @}  @{<loc>%s=%a:$%s@}\n"
@@ -472,9 +430,9 @@ let run_process ?(runtime = false) ?(stubs = false) ?(stdlib = false)
       (* The tests are easier to write with the assumption that shims are
          simply ignored in the Original phase (otherwise they all begin
          [Env.is_renamed env && (* ... *)] *)
-      let runtime = runtime && phase = Renamed in
+      let runtime = runtime && phase <> Original in
       let env =
-        if phase = Renamed && (stubs || stdlib) then
+        if phase <> Original && (stubs || stdlib) then
           apply_shims ~stubs ~stdlib env
         else
           env
@@ -493,7 +451,7 @@ let run_process ?(runtime = false) ?(stubs = false) ?(stdlib = false)
        fails without each shim in turn. The final entry in the strategy must be
        the request itself. *)
     let test_without cond shim strategy =
-      if phase = Renamed && cond then
+      if phase <> Original && cond then
         shim env :: strategy
       else
         strategy
diff --git a/testsuite/tools/environment.mli b/testsuite/tools/environment.mli
index 192718ee3594..217b98f6d56d 100644
--- a/testsuite/tools/environment.mli
+++ b/testsuite/tools/environment.mli
@@ -37,7 +37,7 @@ val make : (Format.formatter -> string -> unit) -> verbose:bool
     with [LD_LIBRARY_PATH] / [DYLD_LIBRARY_PATH] set or updated). *)
 
 val is_renamed : t -> bool
-(** [is_renamed t] if [~phase = Renamed] *)
+(** [is_renamed t] if [~phase <> Original] *)
 
 val test_root : t -> string
 (** Retrieves the [~test_root] passed to {!make}. *)
diff --git a/testsuite/tools/harness.ml b/testsuite/tools/harness.ml
index 6cac18613f36..f57f8e7e1c1d 100644
--- a/testsuite/tools/harness.ml
+++ b/testsuite/tools/harness.ml
@@ -82,11 +82,15 @@ module Import = struct
   type launch_mode = Header_exe | Header_shebang
 
   type executable =
-  | Tendered of {header: launch_mode; dlls: bool; runtime: string}
+  | Tendered of {header: launch_mode;
+                 dlls: bool;
+                 runtime: string;
+                 id: Misc.RuntimeID.t option;
+                 search: Byterntm.search_method}
   | Custom
   | Vanilla
 
-  type phase = Original | Renamed
+  type phase = Original | Execution | Renamed
 
   type mode = Bytecode | Native
 
@@ -94,11 +98,12 @@ module Import = struct
     has_ocamlnat: bool;
     has_ocamlopt: bool;
     has_relative_libdir: string option;
-    has_runtime_search: bool option;
+    has_runtime_search: Config.search_method;
     launcher_searches_for_ocamlrun: bool;
     target_launcher_searches_for_ocamlrun: bool;
     bytecode_shebangs_by_default: bool;
     shebangscripts: bool;
+    filename_mangling: bool;
     libraries: string list list
   }
 
@@ -151,7 +156,7 @@ let files_for ?(source_and_cmi = true) mode name files =
   |> add_if source_and_cmi (name ^ ".ml")
 
 let fail_because fmt =
-  Format.ksprintf (fun s -> prerr_endline s; exit 1) fmt
+  Format.ksprintf (fun s -> flush stdout; prerr_endline s; exit 1) fmt
 
 (* ocamlc cannot be directly executed after renaming the prefix if native
    compilation is disabled (because ocamlc will be ocamlc.byte, since ocamlc.opt
diff --git a/testsuite/tools/harness.mli b/testsuite/tools/harness.mli
index 67d8336026cf..3cdc335fd082 100644
--- a/testsuite/tools/harness.mli
+++ b/testsuite/tools/harness.mli
@@ -23,7 +23,11 @@ module Import : sig
 
   (** Kinds of executable *)
   type executable =
-  | Tendered of {header: launch_mode; dlls: bool; runtime: string}
+  | Tendered of {header: launch_mode;
+                 dlls: bool;
+                 runtime: string;
+                 id: Misc.RuntimeID.t option;
+                 search: Byterntm.search_method}
       (** Tendered bytecode image. Executable uses the given mechanism to locate
           a suitable runtime to execute the image. [dlls] is [true] if the
           bytecode image requires additional C libraries to be loaded. [runtime]
@@ -36,8 +40,11 @@ module Import : sig
 
   (** Test harness phases. *)
   type phase =
-  | Original (* Compiler installed in its original configured prefix. *)
-  | Renamed  (* Compiler moved to a different prefix from its configuration. *)
+  | Original  (* Compiler installed in its original configured prefix. *)
+  | Execution (* Executing programs built by the compiler installed in its
+                 original prefix after the compiler has been moved to a
+                 different prefix. *)
+  | Renamed   (* Compiler moved to a different prefix from its configuration. *)
 
   (* Tooling modes. *)
   type mode =
@@ -53,23 +60,26 @@ module Import : sig
     has_ocamlopt: bool;
       (** {v [$(NATIVE_COMPILER)] v} - {v Makefile.config v} *)
     has_relative_libdir: string option;
-      (** Not implemented; always None. *)
-    has_runtime_search: bool option;
-      (** Not implemented; always None. *)
+      (** {v $(TARGET_LIBDIR_IS_RELATIVE) v} and {v $(TARGET_LIBDIR) v} -
+          {v Makefile.build_config v} *)
+    has_runtime_search: Config.search_method;
+      (** {v $(RUNTIME_SEARCH) v} - {v Makefile.build_config v} *)
     launcher_searches_for_ocamlrun: bool;
       (** Indicates whether bytecode executables in the compiler distribution
-          use a launcher that is capable of searching PATH to find ocamlrun. At
-          present, only native Windows has this behaviour. *)
+          use a launcher that is capable of searching PATH to find ocamlrun.
+          This used to be the behaviour for native Windows. *)
     target_launcher_searches_for_ocamlrun: bool;
       (** Indicates whether the executable launcher used by ocamlc is capable of
-          searching PATH to find ocamlrun. At present, only native Windows has
-          this behaviour. *)
+          searching PATH to find ocamlrun. This used to be the behaviour for
+          native Windows. *)
     bytecode_shebangs_by_default: bool;
       (** True if ocamlc uses a shebang-style header rather than an executable
           header for tendered bytecode executables. *)
     shebangscripts: bool;
       (** {v $(SHEBANGSCRIPTS) v} - {v Makefile.config v} *)
-    libraries: string list list
+    filename_mangling: bool;
+      (** True if the Runtime ID is being used for filename mangling. *)
+    libraries: string list list;
       (** Sorted list of basenames of libraries to test.
           Derived from {v [$(OTHERLIBRARIES)] v} - {v Makefile.config v} *)
   }
diff --git a/testsuite/tools/poisonedruntime.c b/testsuite/tools/poisonedruntime.c
new file mode 100644
index 000000000000..ef5f5be95ea0
--- /dev/null
+++ b/testsuite/tools/poisonedruntime.c
@@ -0,0 +1,27 @@
+/**************************************************************************/
+/*                                                                        */
+/*                                 OCaml                                  */
+/*                                                                        */
+/*            David Allsopp, University of Cambridge & Tarides            */
+/*                                                                        */
+/*   Copyright 2025 David Allsopp Ltd.                                    */
+/*                                                                        */
+/*   All rights reserved.  This file is distributed under the terms of    */
+/*   the GNU Lesser General Public License version 2.1, with the          */
+/*   special exception on linking described in the file LICENSE.          */
+/*                                                                        */
+/**************************************************************************/
+
+/* Micro-program used to sit in PATH to test local path search for bytecode
+   executables. */
+
+#define CAML_INTERNALS
+#include <caml/callback.h>
+#include <stdio.h>
+
+int main_os(int argc, char_os **argv)
+{
+  printf("The poisoned runtime has been invoked!\n"
+         "This suggests something is wrong in stdlib/header.c\n");
+  return 1;
+}
diff --git a/testsuite/tools/testBytecodeBinaries.ml b/testsuite/tools/testBytecodeBinaries.ml
index 536483369ffa..5bc4a97cc0f3 100644
--- a/testsuite/tools/testBytecodeBinaries.ml
+++ b/testsuite/tools/testBytecodeBinaries.ml
@@ -35,126 +35,184 @@ let run config env =
   let exec_magic =
     Environment.run_process env ocamlrun ["-M"]
   in
-  let test_binary binary =
+  let test_binary failed binary =
     if String.starts_with ~prefix:"ocaml" binary
-    || String.starts_with ~prefix:"flexlink" binary then
-    let program = Filename.concat bindir binary in
-    if is_executable program then
-      let classification = Environment.classify_executable program in
-      if classification <> Vanilla then
-        let fails =
-          (* After the prefix has been renamed, bytecode executables compiled
-             with -custom will still work. Otherwise, only executables where the
-             header can search for ocamlrun and which do not require any C stubs
-             to be loaded will still work. *)
-          Environment.is_renamed env
-          && match classification with
-             | Tendered {dlls; _} ->
-                 not config.launcher_searches_for_ocamlrun || dlls
-             | _ ->
-                 false
-        in
-        match Environment.run_process ~fails env program ["-vnum"] with
-        | (0, ((output::rest) as all_output)) when not fails ->
-            if rest <> [] then begin
-              Environment.display_output all_output;
-              Harness.fail_because "%s: expected only one line of output"
-                                   program
-            end;
-            let runtime =
-              let compiled_by_boot_ocamlc =
-                let name =
-                  if Filename.extension binary = ".exe" then
-                    Filename.remove_extension binary
-                  else
-                    binary
-                in
-                name <> "ocamldoc" && name <> "ocamldebug"
-              in
-              match classification with
-              | Vanilla -> assert false
-              | Custom ->
-                  if Config.supports_shared_libraries
-                     || compiled_by_boot_ocamlc then
-                    Harness.fail_because "%s: unexpected -custom runtime"
-                                         program
-                  else
-                    "compiled with -custom"
-              | Tendered {runtime; header; _} ->
-                  let is_expected_runtime =
-                    if Sys.win32 then
-                      runtime = "ocamlrun"
-                    else
-                      runtime = ocamlrun
-                  in
-                  let expected_launch_mode =
-                    if config.shebangscripts then
-                      Header_shebang
+       || String.starts_with ~prefix:"flexlink" binary then
+      let program = Filename.concat bindir binary in
+      if is_executable program then
+        let classification = Environment.classify_executable program in
+        if classification <> Vanilla then
+          let fails =
+            (* After the prefix has been renamed, bytecode executables compiled
+               with -custom will still work. Otherwise, the header needs to be
+               able to search for ocamlrun and, if applicable, ocamlrun needs to
+               be able to load C stubs (which will only happen if the runtime
+               locates the Standard Library using a relative directory, so that
+               it can find ld.conf) *)
+            Environment.is_renamed env
+            && match classification with
+               | Tendered {dlls; _} ->
+                   not config.launcher_searches_for_ocamlrun
+                   || dlls && config.has_relative_libdir = None
+               | _ ->
+                   false
+          in
+          match Environment.run_process ~fails env program ["-vnum"] with
+          | (0, ((output::rest) as all_output)) when not fails ->
+              if rest <> [] then begin
+                Environment.display_output all_output;
+                Harness.fail_because "%s: expected only one line of output"
+                                     program
+              end;
+              let failed, runtime =
+                let compiled_by_boot_ocamlc =
+                  let name =
+                    if Filename.extension binary = ".exe" then
+                      Filename.remove_extension binary
                     else
-                      Header_exe
+                      binary
                   in
-                  if is_expected_runtime then
-                    if header = expected_launch_mode then
-                      runtime
-                    else
-                      Harness.fail_because "%s: unexpected launch mode" program
-                  else
-                    Harness.fail_because "%s: unexpected runtime %S"
-                                         program runtime
-            in
-            Printf.printf "  Runtime: %s\n  Output: %s\n" runtime output;
-            if Sys.win32 && Filename.extension binary = ".exe" then
-              (* This additional part of the test ensures that the executable
-                 launcher on Windows can correctly hand-over to ocamlrun on
-                 Windows. The check is that a binary named ocamlc.byte.exe
-                 can be invoked as ocamlc.byte. -M is used as a previous bug
-                 caused ocamlc.byte to act solely as ocamlrun, the test being
-                 that ocamlrun -M returning the runtime's magic number would
-                 be likely distinct from the behaviour of any of the
-                 distribution's tools when called with -M. *)
-              let without_exe = Filename.remove_extension binary in
-              let (this_exit_code, _) as this =
-                let fails =
-                  without_exe <> "ocamlmklib"
-                  && not (String.contains without_exe '.')
+                  name <> "ocamldoc" && name <> "ocamldebug"
                 in
-                Environment.run_process
-                  ~fails env program ~argv0:without_exe ["-M"]
+                match classification with
+                | Vanilla -> assert false
+                | Custom ->
+                    if Config.supports_shared_libraries
+                       || compiled_by_boot_ocamlc then
+                      Harness.fail_because "%s: unexpected -custom runtime"
+                                           program
+                    else
+                      failed, "compiled with -custom"
+                | Tendered {runtime; id; header; search; _} ->
+                    let reported_runtime, search =
+                      let id =
+                        Option.map
+                          (fun t -> "-" ^ Misc.RuntimeID.to_string t) id
+                        |> Option.value ~default:""
+                      in
+                      match search with
+                      | Disable dir ->
+                          dir ^ runtime ^ id, Config.Disable
+                      | Fallback dir ->
+                          Printf.sprintf "[%s]%s%s" dir runtime id,
+                          Config.Fallback
+                      | Enable ->
+                          runtime ^ id, Config.Enable
+                    in
+                    let expected_id =
+                      if config.filename_mangling then
+                        Some (Misc.RuntimeID.make_zinc ())
+                      else
+                        None
+                    in
+                    let expected_launch_mode =
+                      if config.shebangscripts then
+                        Header_shebang
+                      else
+                        Header_exe
+                    in
+                    let pp_runtime_id f = function
+                    | None ->
+                        Format.pp_print_string f "<NONE>"
+                    | Some id ->
+                        Format.pp_print_string f (Misc.RuntimeID.to_string id)
+                    in
+                    let pp_search f = function
+                    | Config.Disable ->
+                        Format.pp_print_string f "disable"
+                    | Config.Fallback ->
+                        Format.pp_print_string f "fallback"
+                    | Config.Enable ->
+                        Format.pp_print_string f "enable"
+                    in
+                    let pp_launch f = function
+                    | Header_shebang -> Format.pp_print_string f "shebang"
+                    | Header_exe -> Format.pp_print_string f "executable"
+                    in
+                    let check expected actual description print failed =
+                      if expected = actual then
+                        failed
+                      else
+                        Format.kfprintf (Fun.const true) Format.err_formatter
+                          "  *** Unexpected %s (Expected: %a; got %a)\n%!"
+                          description print expected print actual
+                    in
+                    let failed =
+                      failed
+                      |> check config.has_runtime_search search
+                               "search mechanism" pp_search
+                      |> check expected_id id
+                               "runtime ID" pp_runtime_id
+                      |> check "ocamlrun" runtime
+                               "runtime" Format.pp_print_string
+                      |> check expected_launch_mode header
+                               "launch mode" pp_launch
+                    in
+                    failed, reported_runtime
               in
-              if this_exit_code = 0 then
-                if this = exec_magic then
-                  let (that_exit_code, _) as that =
-                    let fails = without_exe <> "ocamlmklib" in
-                    Environment.run_process
-                      ~fails env program ~argv0:binary ["-M"]
-                  in
-                  if this = that then
-                    Harness.fail_because
-                      "Neither %s nor %s seem to load the bytecode image"
-                      without_exe binary
-                  else if that_exit_code = 0 then
-                    Harness.fail_because
-                      "%s is not expected to return with exit code 0"
-                      binary
-                  else if not (String.contains without_exe '.') then
+              Printf.printf "  Runtime: %s\n  Output: %s\n" runtime output;
+              if Sys.win32 && Filename.extension binary = ".exe" then begin
+                (* This additional part of the test ensures that the executable
+                   launcher on Windows can correctly hand-over to ocamlrun on
+                   Windows. The check is that a binary named ocamlc.byte.exe
+                   can be invoked as ocamlc.byte. -M is used as a previous bug
+                   caused ocamlc.byte to act solely as ocamlrun, the test being
+                   that ocamlrun -M returning the runtime's magic number would
+                   be likely distinct from the behaviour of any of the
+                   distribution's tools when called with -M. *)
+                let without_exe = Filename.remove_extension binary in
+                let (this_exit_code, _) as this =
+                  let fails =
+                    without_exe <> "ocamlmklib"
+                    && not (String.contains without_exe '.') in
+                  Environment.run_process
+                    ~fails env program ~argv0:without_exe ["-M"]
+                in
+                if this_exit_code = 0 then
+                  if this = exec_magic then
+                    let (that_exit_code, _) as that =
+                      let fails = without_exe <> "ocamlmklib" in
+                      Environment.run_process
+                        ~fails env program ~argv0:binary ["-M"]
+                    in
+                    if this = that then
+                      Harness.fail_because
+                        "Neither %s nor %s seem to load the bytecode image"
+                        without_exe binary
+                    else if that_exit_code = 0 then
+                      Harness.fail_because
+                        "%s is not expected to return with exit code 0"
+                        binary
+                    else if not (String.contains without_exe '.') then
+                      Harness.fail_because
+                        "%s is not expected to return the exec magic number!"
+                        without_exe
+                    else () (* Expected outcome was the exec magic number *)
+                  else if without_exe <> "ocamlmklib" then
                     Harness.fail_because
-                      "%s is not expected to return the exec magic number!"
+                      "%s is expected to return with a non-zero exit code"
                       without_exe
-                  else () (* Expected outcome was the exec magic number *)
-                else if without_exe <> "ocamlmklib" then
+                  else () (* Expected outcome is a zero exit code *)
+                else if without_exe = "ocamlmklib" then
                   Harness.fail_because
-                    "%s is expected to return with a non-zero exit code"
+                    "%s is expected to return with exit code 0"
                     without_exe
-                else () (* Expected outcome is a zero exit code *)
-              else if without_exe = "ocamlmklib" then
-                Harness.fail_because
-                  "%s is expected to return with exit code 0"
-                  without_exe
-              else () (* Expected outcome is a non-zero exit code *)
-        | _ ->
-            if not fails then
-              Harness.fail_because "%s: not expected to have failed" program
+                else () (* Expected outcome is a non-zero exit code *)
+              end;
+              failed
+          | _ ->
+              if not fails then
+                Harness.fail_because "%s: not expected to have failed" program
+              else
+                failed
+        else
+          failed
+      else
+        failed
+    else
+      failed
   in
   let binaries = Sys.readdir bindir in
   Array.sort String.compare binaries;
-  Array.iter test_binary binaries
+  if Array.fold_left test_binary false binaries then
+    Harness.fail_because "Binaries didn't all match expectation"
diff --git a/testsuite/tools/testDynlink.ml b/testsuite/tools/testDynlink.ml
index d34563ff88e8..ad6611eff343 100644
--- a/testsuite/tools/testDynlink.ml
+++ b/testsuite/tools/testDynlink.ml
@@ -48,14 +48,25 @@ let () =
     let compile ?(custom = false) () =
       if Sys.file_exists test_program then
         Harness.erase_file test_program;
-      let args = if custom then "-custom" :: args else args in
+      let args =
+        if custom then
+          "-custom" :: args
+        else
+          (* Hardening to ensure that Bytecode Dynlink is using the runtime's
+             search path, not compiler's (i.e. unix.cma should be located using
+             Config.standard_library_default but dllunixbyt.so should be located
+             using caml_runtime_standard_library_default) *)
+          "-set-runtime-default" :: "standard_library_default=/does-not-exist"
+          :: args
+      in
       (* In the Renamed phase for a bytecode-only build, ocamlc will be
          ocamlc.byte and will need to be called via ocamlrun *)
       let runtime =
         mode = Bytecode && Harness.ocamlc_fails_after_rename config in
       (* In the Renamed phase, Config.standard_library will still point to the
-         Original location *)
-      let stdlib = true in
+         Original location, unless the compiler has been configured with a
+         relative libdir *)
+      let stdlib = (config.has_relative_libdir = None) in
       let (_, output) =
         Environment.run_process ~runtime ~stdlib env compiler args in
       Environment.display_output output
@@ -78,12 +89,15 @@ let () =
       mode = Bytecode
       && expected_exit_code = None
       && not config.target_launcher_searches_for_ocamlrun
+      && config.has_relative_libdir = None
     in
     (* If the library needs C stubs to be loaded dynamically, then the runtime
        will need CAML_LD_LIBRARY_PATH set in the Renamed phase. *)
     let stubs =
       has_c_stubs
       && expected_exit_code = None
+      && Config.supports_shared_libraries
+      && config.has_relative_libdir = None
     in
     let expected_exit_code =
       match expected_exit_code with
@@ -126,11 +140,16 @@ let () =
   let not_dynlink l = not (List.mem "dynlink" l) in
   let files, re_compile = compile_test_program () in
   let expected_exit_code =
-    (* Bytecode executables launched using the executable header require
-       caml_executable_name to know where the runtime is. As the Standard
-       Library is only stored as an absolute path, this doesn't affect the
-       execution of the test driver (yet). *)
-    None in
+    (* Relocatable OCaml bytecode executables launched using the executable
+       header require caml_executable_name, or they end up being accidentally
+       relative, since the exec call leaves argv[0] as being the bytecode image
+       itself. *)
+    if mode = Bytecode && config.has_relative_libdir <> None
+       && Harness.no_caml_executable_name
+       && Environment.launched_via_stub test_program then
+      Some 2
+    else
+      None in
   let libraries = List.filter not_dynlink config.libraries in
   let () =
     List.iter (test_libraries_in_prog ?expected_exit_code env) libraries;
diff --git a/testsuite/tools/testLinkModes.ml b/testsuite/tools/testLinkModes.ml
index a7c4d0be1fb5..7fbfbf1afdc4 100644
--- a/testsuite/tools/testLinkModes.ml
+++ b/testsuite/tools/testLinkModes.ml
@@ -125,7 +125,7 @@ let () =
    around some problems with shared runtimes on s390x and riscv which don't
    reliably fail.
 *)
-let run_program env _config =
+let run_program env config =
   let prefix = Environment.prefix env in
   let libdir_suffix = Environment.libdir_suffix env in
   let prefix, libdir_suffix =
@@ -142,7 +142,7 @@ let run_program env _config =
       if Environment.is_renamed env then
         stdlib_exists_when_renamed
       else
-        true in
+        config.has_relative_libdir <> None in
     let args = [string_of_bool stdlib_exists; prefix; libdir_suffix] in
     let argv0 =
       if argv0 = test_program then
@@ -270,7 +270,7 @@ type outcome =
    - Sys.argv.(0) doesn't equal Sys.argv.(3)
    - Config.standard_library exists when it shouldn't (or vice versa) *)
 let test_runs usr_bin_sh test_program_path test_program
-              _config env ~via_ocamlrun =
+              config env ~via_ocamlrun =
   let tests =
     let test_program_relative =
       Filename.concat Filename.current_dir_name test_program
@@ -313,7 +313,7 @@ let test_runs usr_bin_sh test_program_path test_program
         | Tendered {header = Header_exe; _} ->
             if argv0_not_ocaml then
               if Sys.win32 then
-                (* stdlib/headernt.c will find ocamlrun (because it effectively
+                (* stdlib/header.c will find ocamlrun (because it effectively
                    uses caml_executable_name) but fails to hand off the bytecode
                    image, which causes ocamlrun to exit with code 127 *)
                 Fail 127
@@ -324,10 +324,16 @@ let test_runs usr_bin_sh test_program_path test_program
                    executable. Somewhat confusingly, it exits with code 2 *)
                 Fail 2
             else if Sys.win32 then
-              (* stdlib/headernt.c correctly preserves argv[0] *)
+              (* stdlib/header.c correctly preserves argv[0] for Windows *)
               Success {executable_name = test_program_path; argv0}
+            else if Harness.no_caml_executable_name
+                    && config.has_relative_libdir <> None then
+              (* Without caml_executable_name, ocamlrun will be forced to
+                 interpret the relative standard library relative to argv[0],
+                 which will fail. *)
+              Fail 134
             else
-              (* stdlib/header.c does not preserve argv[0] *)
+              (* stdlib/header.c does not preserve argv[0] for Unix *)
               Success {executable_name = argv0_resolved;
                        argv0 = argv0_resolved}
         | Custom ->
@@ -340,12 +346,8 @@ let test_runs usr_bin_sh test_program_path test_program
               else
                 Success {executable_name = argv0_resolved; argv0}
             else
-              if Sys.win32 || argv0_not_ocaml then
-                (* SearchPath will resolve the relative/implicit arguments to
-                   absolute paths *)
-                Success {executable_name = test_program_path; argv0}
-              else
-                Success {executable_name = argv0_resolved; argv0}
+              (* -custom executables use caml_executable_name *)
+              Success {executable_name = test_program_path; argv0}
         | Vanilla ->
             if Harness.no_caml_executable_name then
               Success {executable_name = argv0_resolved; argv0}
@@ -366,23 +368,53 @@ let test_runs usr_bin_sh test_program_path test_program
    run in the Renamed phase for other reasons. *)
 let make_test_runner ~stdlib_exists_when_renamed ~may_segfault ~with_unix
                      ~tendered ~target_launcher_searches_for_ocamlrun usr_bin_sh
-                     test_program_path test_program config _env =
-  (* Bytecode executables with absolute headers will need to be
-     invoked via ocamlrun after the prefix has been renamed. *)
+                     test_program_path test_program config env =
+  (* Bytecode executables with absolute headers will need to be invoked via
+     ocamlrun after the prefix has been renamed. *)
   let via_ocamlrun =
     tendered && not target_launcher_searches_for_ocamlrun
+    && (config.has_relative_libdir = None || not (Environment.is_renamed env))
   in
-  let rec run env =
+  let rec run ~re_executing env =
     let runs =
       test_runs usr_bin_sh test_program_path test_program
                 config env ~via_ocamlrun in
     let execute ({argv0; prefix_path_with_cwd}, outcome) =
       let expected_executable_name, expected_exit_code, expected_argv0 =
         match outcome with
-        | Fail code -> "", code, ""
-        | Success {executable_name; argv0} -> executable_name, 0, argv0
+        | Fail code ->
+            "", code, ""
+        | Success {executable_name; argv0} ->
+            (* Systems which don't have caml_executable_name get particularly
+               fiddly here, because they can fail for multiple reasons in this
+               test! Any tendered executable which was expected to succeed is
+               set to fail here, since the shim for CAML_LD_LIBRARY_PATH will
+               not be applied. *)
+            if tendered && with_unix && Harness.no_caml_executable_name
+               (* Passing the executable directly to ocamlrun will fail if
+                  ocamlrun isn't configured with a relative libdir *)
+               && (not via_ocamlrun || config.has_relative_libdir = None)
+               && (re_executing || Environment.is_renamed env
+                                   && config.has_relative_libdir = None) then
+              "", 134, ""
+            else
+              executable_name, 0, argv0
+      in
+      let stubs =
+        tendered && with_unix
+        (* The programs compiled before the prefix is renamed are intentionally
+           run without the runtime in PATH in order to test the bytecode
+           launcher's searching in the image directory before PATH. A side
+           effect of this is that ld.conf then can't be found, because the
+           runtime copied to the testsuite directory doesn't have ld.conf in the
+           correct place. The shim is skipped for systems which don't have
+           caml_executable_name because otherwise we'd have a test which fails
+           in the Original phase and succeeds in the Execution phase, which is a
+           special case too far! *)
+        && (not Harness.no_caml_executable_name
+            && (config.has_relative_libdir = None
+                || not via_ocamlrun && re_executing))
       in
-      let stubs = tendered && with_unix in
       run_program
         env config ~runtime:via_ocamlrun ~stubs
         test_program_path ~prefix_path_with_cwd expected_executable_name
@@ -394,14 +426,14 @@ let make_test_runner ~stdlib_exists_when_renamed ~may_segfault ~with_unix
     if Environment.is_renamed env then
       (Harness.erase_file test_program_path; `None)
     else
-      `Some run
+      `Some (run ~re_executing:true)
   in
-  `Some run
+  `Some (run ~re_executing:false)
 
 (* Describe the various ways in which executables can be produced by our two
    compilers... *)
 type linkage =
-| Default_ocamlc of launch_mode
+| Default_ocamlc of launch_mode * Config.search_method
 | Default_ocamlopt
 | Custom_runtime of runtime_mode
 | Output_obj of compiler * runtime_mode
@@ -470,8 +502,34 @@ let compile_test usr_bin_sh config env test test_program description =
           0
       in
       match test with
-      | Default_ocamlc _launch_method ->
-          f ~tendered:true []
+      | Default_ocamlc(launch_method, search_method) ->
+          let args =
+            match launch_method with
+            | Header_exe when config.bytecode_shebangs_by_default ->
+                ["-launch-method"; "exe"]
+            | Header_shebang when not config.bytecode_shebangs_by_default ->
+                ["-launch-method"; "sh"]
+            | _ ->
+                [] in
+          let target_launcher_searches_for_ocamlrun =
+            if search_method = Config.search_method then
+              None
+            else
+              Some (search_method <> Config.Disable)
+          in
+          let param =
+            match search_method with
+            | Disable -> "disable"
+            | Fallback -> "fallback"
+            | Enable -> "enable"
+          in
+          let args =
+            if search_method = Config.search_method then
+              args
+            else
+              "-runtime-search" :: param :: args
+          in
+          f ?target_launcher_searches_for_ocamlrun ~tendered:true args
       | Default_ocamlopt ->
           f ~mode:Native []
       | Custom_runtime Static ->
@@ -493,7 +551,7 @@ let compile_test usr_bin_sh config env test test_program description =
       | Output_obj(C_ocamlopt, Static) ->
           f ~mode:Native
             ~clibs:["-lcomprmarsh"; "-lunixnat";
-                    Toolchain.compression_c_libraries]
+                    Config.compression_c_libraries]
             ["-output-obj"]
       | Output_obj(C_ocamlopt, Shared) ->
           (* cf. ocaml/ocaml#13693 - on Fedora/RHEL, this executable
@@ -504,7 +562,7 @@ let compile_test usr_bin_sh config env test test_program description =
           let linker_exit_code = fails_if (Sys.win32 || Sys.cygwin) in
           f ~mode:Native ~use_shared_runtime:true ~may_segfault
             ~clibs:["-lcomprmarsh"; "-lunixnat";
-                    Toolchain.compression_c_libraries]
+                    Config.compression_c_libraries]
             ~linker_exit_code ["-output-obj"]
       | Output_complete_obj(C_ocamlc, Static) ->
           (* At the moment, the partial linker will pass -lws2_32 and -ladvapi32
@@ -534,15 +592,16 @@ let compile_test usr_bin_sh config env test test_program description =
           (* At the moment, the partial linker will pass -lzstd to ld -r which
              will (normally) fail). Until this is done, pass the libraries
              manually, using -noautolink. *)
-          f ~mode:Native ~clibs:[Toolchain.compression_c_libraries]
+          f ~mode:Native ~clibs:[Config.compression_c_libraries]
             ~linker_exit_code
             ["-output-complete-obj"; "-noautolink"; "-cclib"; "-lunixnat";
                                                     "-cclib"; "-lcomprmarsh"]
       | Output_complete_obj(C_ocamlopt, Shared) ->
-          (* ocamlopt doesn't correctly implement -runtime-variant _shared *)
-          let compilation_exit_code = fails_if true in
+          (* ocamlopt allows the .so to be passed to the partial linker which
+             fails with GNU ld, but not with the macOS linker *)
+          let compilation_exit_code = fails_if (Config.system <> "macosx") in
           f ~mode:Native ~use_shared_runtime:true
-            ~compilation_exit_code ~clibs:[Toolchain.compression_c_libraries]
+            ~compilation_exit_code ~clibs:[Config.compression_c_libraries]
             ["-output-complete-obj"; "-noautolink"; "-cclib"; "-lunixnat";
                                                     "-cclib"; "-lcomprmarsh"]
       | Output_complete_exe Static ->
@@ -579,6 +638,21 @@ let compile_test usr_bin_sh config env test test_program description =
         else
           options
       in
+      let options =
+        if Environment.is_renamed env || config.has_relative_libdir <> None then
+          options
+        else
+          let new_libdir =
+            Filename.concat (Environment.prefix env ^ ".new")
+                            (Environment.libdir_suffix env) in
+          let stdlib_default = "standard_library_default=" ^ new_libdir in
+          let options = "-set-runtime-default" :: stdlib_default :: options in
+          if tendered then
+            let libdir = Environment.libdir env in
+            "-dllpath" :: (Filename.concat libdir "stublibs") :: options
+          else
+            options
+      in
       let args =
         "-o" :: output ::
         "test_install_script.ml" :: options
@@ -605,14 +679,11 @@ let compile_test usr_bin_sh config env test test_program description =
              need to be invoked via ocamlrun in the Renamed phase *)
           let runtime =
             mode = Bytecode && Harness.ocamlc_fails_after_rename config in
-          (* If shared libraries are being used, ocamlc will need to be able to
-             load the stub libraries to check the primitives table *)
-          let stubs = with_unix && tendered in
           (* In the Renamed phase, Config.standard_library will still point to
-             the Original location *)
-          let stdlib = true in
-          Environment.run_process
-            ~fails ~runtime ~stubs ~stdlib env compiler args
+             the Original location, unless the compiler has been configured
+             with a relative libdir *)
+          let stdlib = (config.has_relative_libdir = None) in
+          Environment.run_process ~fails ~runtime ~stdlib env compiler args
         in
         Environment.display_output output;
         exit_code
@@ -639,9 +710,21 @@ let compile_test usr_bin_sh config env test test_program description =
           `None
         else
           let stdlib_exists_when_renamed =
-            (* Config.standard_library is an absolute path, and therefore will
-               always point to the Original location in the Renamed phase. *)
-            false
+            if config.has_relative_libdir = None then
+              (* In the Original phase, for a compiler with an absolute libdir,
+                 -set-runtime-default is used to set standard_library_default to
+                 the Renamed phase's location. When the tests are recompiled in
+                 the Renamed phase, this is not done. The effect is that if any
+                 test is being run in the Renamed phase, Config.standard_library
+                 will be correct. *)
+              not (Environment.is_renamed env)
+            else
+              (* When the compiler has a relative libdir, -set-runtime-default
+                 is implicitly being tested by the build process, and we wish to
+                 test the opposite in the harness - thus the test programs
+                 compiled in the Original phase will _not_ be able to find the
+                 Standard Library in the Renamed phase. *)
+              Environment.is_renamed env
           in
           make_test_runner ~stdlib_exists_when_renamed ~may_segfault ~with_unix
                            ~tendered ~target_launcher_searches_for_ocamlrun
@@ -673,15 +756,13 @@ let run ~sh config env =
   Format.printf "ocamlc -where: %a\nocamlopt -where: %a\n%!"
                 pp_path ocamlc_where pp_path ocamlopt_where;
   let compile_test = compile_test sh config env in
-  let launch_method =
-    if config.bytecode_shebangs_by_default then
-      Header_shebang
-    else
-      Header_exe
-  in
   let tests = [
-    compile_test (Default_ocamlc launch_method)
-      "byt_default" "with tender";
+    compile_test (Default_ocamlc(Header_exe, Disable))
+      "byt_default_exe_disable" "with absolute tender";
+    compile_test (Default_ocamlc(Header_exe, Fallback))
+      "byt_default_exe_fallback" "with fallback tender";
+    compile_test (Default_ocamlc(Header_exe, Enable))
+      "byt_default_exe_enable" "with relocatable tender";
     compile_test (Custom_runtime Static)
       "custom_static" "-custom static runtime";
     compile_test (Custom_runtime Shared)
@@ -709,5 +790,16 @@ let run ~sh config env =
     compile_test (Output_complete_obj(C_ocamlopt, Shared))
       "nat_complete_obj_shared" "-output-complete-obj shared runtime";
   ] in
+  let tests =
+    if config.shebangscripts then
+      (compile_test (Default_ocamlc(Header_shebang, Disable))
+        "byt_default_sh_disable" "with absolute #!") ::
+      (compile_test (Default_ocamlc(Header_shebang, Fallback))
+        "byt_default_sh_fallback" "with fallback #!") ::
+      (compile_test (Default_ocamlc(Header_shebang, Enable))
+        "byt_default_sh_enable" "with relocatable #!") ::
+      tests
+    else
+      tests in
   Printf.printf "Running programs\n%!";
   List.map (function `Some f -> f env | `None -> `None) tests
diff --git a/testsuite/tools/testRelocation.ml b/testsuite/tools/testRelocation.ml
index aa3439d9228f..6a2ff3ce6c42 100644
--- a/testsuite/tools/testRelocation.ml
+++ b/testsuite/tools/testRelocation.ml
@@ -27,12 +27,17 @@ module LocationMap = Map.Make(Location)
 (* Augment toolchain properties with information from the configuration (this
    essentially goes from "is foo capable of doing bar" to "foo does bar in this
    context". *)
-let effective_toolchain _config =
+let effective_toolchain config =
   let c_compiler_debug_paths_are_absolute =
     Toolchain.c_compiler_debug_paths_can_be_absolute
+    && (not Config.c_has_debug_prefix_map || config.has_relative_libdir = None)
   in
   let assembler_embeds_build_path =
     Toolchain.assembler_embeds_build_path
+    && (not Config.as_has_debug_prefix_map
+        || Config.architecture = "riscv"
+        || Toolchain.as_is_cc
+        || config.has_relative_libdir = None)
   in
   c_compiler_debug_paths_are_absolute, assembler_embeds_build_path
 
@@ -62,18 +67,20 @@ let bindir_rules config file =
     (* Determine if the installation prefix should be found in this file *)
     let prefix =
       let code_embeds_stdlib_location =
-        (* The runtime binaries all contain OCAML_STDLIB_DIR and everything
-           except flexlink and ocamllex link with the Config module, either
-           directly or via ocamlcommon *)
-        not (List.mem basename ["flexlink.byte"; "flexlink.opt"; "flexlink";
-                                "ocamllex.byte"; "ocamllex.opt"; "ocamllex";
-                                "ocamlyacc"])
+        (* If the compiler is configured with an absolute libdir, the runtime
+           binaries all contain OCAML_STDLIB_DIR and everything except flexlink
+           and ocamllex link with the Config module, either directly or via
+           ocamlcommon *)
+        config.has_relative_libdir = None
+        && not (List.mem basename ["flexlink.byte"; "flexlink.opt"; "flexlink";
+                                   "ocamllex.byte"; "ocamllex.opt"; "ocamllex";
+                                   "ocamlyacc"])
       in
       let linker_embeds_stdlib_location =
         (* If the launcher doesn't search for ocamlrun, then either the #! stub
            will include the absolute path or the RNTM section will *)
         match classification with
-        | Tendered _ when not config.launcher_searches_for_ocamlrun -> true
+        | Tendered _ when config.has_runtime_search <> Config.Enable -> true
         | _ -> false
       in
       if code_embeds_stdlib_location || linker_embeds_stdlib_location then
@@ -107,7 +114,7 @@ let bindir_rules config file =
       else
         (* Bytecode runtimes and ocamlyacc of which only ocamlrund is linked
            with -g *)
-        `Other, (basename = "ocamlrund")
+        `Other, (List.mem "ocamlrund" (String.split_on_char '-' basename))
     in
     (* Combine this with the properties of the platform to determine whether the
        executable will contain the build path. *)
@@ -127,7 +134,7 @@ let bindir_rules config file =
              stripped. However, since the C objects in libcamlrun are compiled
              with -g, this will still result in debug information for -custom
              runtime executables. *)
-          linked_with_debug
+          linked_with_debug && config.has_relative_libdir = None
           || (classification = Custom
               && Toolchain.linker_propagates_debug_information
               && c_compiler_debug_paths_are_absolute)
@@ -161,18 +168,20 @@ let libdir_rules config file =
        - contains objects which have been created by the assembler *)
     let (embeds_stdlib_location, has_ocaml_debug_info, has_c_debug_info,
          contains_assembled_objects) =
-      if List.mem basename ["Makefile.config";
-                            "ld.conf";
-                            "runtime-launch-info"] then
-        (* These files all embed the Standard Library location *)
+      if basename = "Makefile.config" then
+        (* Embeds the Standard Library location *)
         (true, false, false, false)
       else if basename = "config.cmx" then
         (* config.cmx contains Config.standard_library for inlining *)
-        (true, false, false, false)
+        let stdlib =
+          config.has_relative_libdir = None && not Config.flambda in
+        (stdlib, false, false, false)
       else if List.mem ext [".cma"; ".cmo"; ".cmt"; ".cmti"] then
         let stdlib = (* via Config.standard_library *)
-          List.mem basename ["config.cmt"; "config_main.cmt";
-                             "ocamlcommon.cma"] in
+          config.has_relative_libdir = None
+          && List.mem basename ["config.cmt"; "config_main.cmt";
+                                "ocamlcommon.cma"] in
+        (* The compiler's artefacts are all compiled with -g *)
         (stdlib, true, false, false)
       else if ext = ".cmxs" then
         (* All the .cmxs files built by the distribution at present include C
@@ -188,16 +197,6 @@ let libdir_rules config file =
           not (is_ocaml || String.starts_with ~prefix:"flexdll_" basename) in
         (false, false, c_debug, is_ocaml)
       else if ext = Config.ext_lib || ext = Config.ext_dll then
-        (* Based on the filename, is this one of the bytecode runtime libraries
-           (libcamlrun.a, libcamlrund.a, libcamlrun_shared.so, etc.
-           Note that these properties are _not_ used for libasmrun* (see
-           below) *)
-        let is_camlrun =
-          let dir = Filename.basename (Filename.dirname file) in
-          dir <> "stublibs"
-            && String.starts_with ~prefix:"libcamlrun" basename
-            && not (String.starts_with ~prefix:"libcamlruntime" basename)
-        in
         if ext = Config.ext_lib then
           (* Any archive produced by ocamlopt will have a .cmxa file with it *)
           let is_ocaml =
@@ -205,14 +204,13 @@ let libdir_rules config file =
           (* Config.standard_library is in ocamlcommon and the bytecode runtime
              embeds the Standard Library location *)
           let stdlib =
-            is_camlrun
-            || Filename.remove_extension basename = "ocamlcommon"
-          in
+            config.has_relative_libdir = None
+            && Filename.remove_extension basename = "ocamlcommon" in
           (stdlib, false, (not is_ocaml), is_ocaml)
         else
           (* DLLs are either the shared versions of the runtime libraries or
              C stubs. All of these are compiled with -g *)
-          (is_camlrun, false, true, false)
+          (false, false, true, false)
       else
         (false, false, false, false)
     in
@@ -230,7 +228,7 @@ let libdir_rules config file =
              || Toolchain.linker_embeds_build_path) then
         Toolchain.linker_embeds_build_path
       else
-        has_ocaml_debug_info
+        has_ocaml_debug_info && config.has_relative_libdir = None
         || has_c_debug_info && c_compiler_debug_paths_are_absolute
         || contains_assembled_objects && assembler_embeds_build_path
         || ext = Config.ext_obj
@@ -242,8 +240,29 @@ let libdir_rules config file =
       else
         LocationMap.empty
     in
+    let prefix =
+      if config.has_relative_libdir <> None
+         && basename = "Makefile.config" then
+        LocationMap.add Relative false prefix
+      else
+        prefix
+    in
     if contains_build_path then
       LocationMap.add Build false prefix
+    (* Prior to #13828 (OCaml 5.4.0), .cmt and .cmti embed the absolute location
+       of the compiler without using BUILD_PATH_PREFIX_MAP. However, this
+       embedding is not entirely predictable, because it only happens when
+       ocamlc.opt or ocamlopt.opt is used for compilation, rather than when the
+       bytecode version of the tool is passed is explicitly to ocamlrun (in this
+       case, Sys.argv.(0) always retains the relative path used in the build
+       system). For this reason, when configured relatively, on Windows, with
+       native compilation available, accept that the Build directory may appear
+       in .cmt/.cmti files. *)
+    else if config.has_relative_libdir <> None
+            && Sys.win32
+            && config.has_ocamlopt
+            && (ext = ".cmt" || ext = ".cmti") then
+      LocationMap.add Build true prefix
     else
       prefix
 
@@ -288,18 +307,8 @@ let rec contains content content_len tests i seen =
         seen, i in
     contains content content_len tests (i + 1) seen
 
-let rec to_utf_8_seq b i () =
-  if i >= Bytes.length b then
-    Seq.Nil
-  else
-    let next = Bytes.get_utf_8_uchar b i in
-    let u = Uchar.utf_decode_uchar next in
-    Seq.Cons(u, to_utf_8_seq b (i + Uchar.utf_decode_length next))
-
-let to_utf_8_seq s = to_utf_8_seq (Bytes.unsafe_of_string s) 0
-
 let utf_16le_of_utf_8 s =
-  let s = to_utf_8_seq s in
+  let s = Bytelink.to_utf_8_seq s in
   let utf_16le_length =
     Seq.fold_left (fun acc u -> acc + Uchar.utf_16_byte_length u) 0 s in
   let b = Bytes.create utf_16le_length in
@@ -503,17 +512,6 @@ let run ~reproducible config env =
     |> scan Environment.libdir "$libdir" libdir_rules
   in
   flush stderr;
-  (* Abort the harness if there are files which didn't match a ruleset *)
-  let () =
-    if results_are_reproducible && not consistent then
-      Harness.fail_because
-        "Internal error: bindir_rules and libdir_rules disagree with \
-         reproducible_rules"
-    else if results_are_reproducible <> reproducible then
-      Harness.fail_because
-        "The build is %sexpected to be reproducible"
-        (if not reproducible then "not " else "")
-  in
   (* Summarise the results, using wildcards to bring them to a readable
      length *)
   let sections =
@@ -632,7 +630,15 @@ let run ~reproducible config env =
     let pp_results = Format.(pp_print_list ~pp_sep pp_print_string) in
     Format.printf "@[<hov 4>  %a@]@." pp_results results
   in
+  (* Abort the harness if there are files which didn't match a ruleset *)
   if failed then
-    Harness.fail_because "Installed files don't match expectation"
-  else
-  List.iter display sections
+    Harness.fail_because "Installed files don't match expectation";
+  List.iter display sections;
+  if results_are_reproducible && not consistent then
+    Harness.fail_because
+      "Internal error: bindir_rules and libdir_rules disagree with \
+       reproducible_rules"
+  else if results_are_reproducible <> reproducible then
+    Harness.fail_because
+      "The build is %sexpected to be reproducible"
+      (if not reproducible then "not " else "")
diff --git a/testsuite/tools/testToplevel.ml b/testsuite/tools/testToplevel.ml
index 665371261129..699ead0dd8b5 100644
--- a/testsuite/tools/testToplevel.ml
+++ b/testsuite/tools/testToplevel.ml
@@ -97,8 +97,7 @@ let run config env mode =
       Environment.run_process
         ~fails:(expected_exit_code <> 0)
         ~runtime:(mode = Bytecode && not config.launcher_searches_for_ocamlrun)
-        ~stubs:(mode = Bytecode && has_c_stubs)
-        ~stdlib:true env toplevel args
+        ~stdlib:(config.has_relative_libdir = None) env toplevel args
     in
     Environment.display_output output;
     if exit_code <> expected_exit_code then
diff --git a/testsuite/tools/test_in_prefix.ml b/testsuite/tools/test_in_prefix.ml
index 743ea1996505..4764b185d2fa 100644
--- a/testsuite/tools/test_in_prefix.ml
+++ b/testsuite/tools/test_in_prefix.ml
@@ -49,13 +49,13 @@ let print_summary config header_size ~prefix ~bindir_suffix ~libdir_suffix
     \    @{<hint>libdir@} = [$prefix/]%s\n\
     \  - C compiler is %s [%s] for %s\n\
     \  - OCaml is %a%a; target binaries by default are %a\n\
-    \  - Executable header size is %.2fKiB (%d bytes)\n\
+    \  - Executable header size is %.2fKiB (%Ld bytes)\n\
     \  - Testing %s\n@?"
        prefix bindir_suffix libdir_suffix
        Config.c_compiler Toolchain.c_compiler_vendor Config.target
        pp_relocatable relocatable pp_reproducible reproducible
        pp_relocatable target_relocatable
-       (float_of_int header_size /. 1024.0) header_size summary
+       (Int64.to_float header_size /. 1024.0) header_size summary
 
 let run_tests ~sh config env =
   TestDynlink.run config env Bytecode;
@@ -68,41 +68,9 @@ let run_tests ~sh config env =
   TestBytecodeBinaries.run config env;
   TestLinkModes.run ~sh config env
 
-type launch_method =
-| Shebang_bin_sh of string
-| Executable
-
-type runtime_launch_info = {
-  buffer : string;
-  launcher : launch_method;
-  executable_offset : int
-}
-
-let read_runtime_launch_info file =
-  let buffer =
-    try
-      In_channel.with_open_bin file In_channel.input_all
-    with Sys_error msg -> Harness.fail_because "%s: %s" file msg
-  in
-  try
-    let bindir_start = String.index buffer '\n' + 1 in
-    let bindir_end = String.index_from buffer bindir_start '\000' in
-    let executable_offset = bindir_end + 2 in
-    let launcher =
-      let kind = String.sub buffer 0 (bindir_start - 1) in
-      if kind = "exe" then
-        Executable
-      else if kind <> "" && (kind.[0] = '/' || kind = "sh") then
-        Shebang_bin_sh kind
-      else
-        raise Not_found in
-    if String.length buffer < executable_offset
-       || buffer.[executable_offset - 1] <> '\n' then
-      raise Not_found
-    else
-      {launcher; buffer; executable_offset}
-  with Not_found ->
-    Harness.fail_because "%s: corrupt header" file
+let rename_exe_in_test_root env from_base to_base =
+  Sys.rename (Environment.in_test_root env (Harness.exe from_base))
+             (Environment.in_test_root env (Harness.exe to_base))
 
 let () =
   let config, pwd, prefix, _, bindir_suffix, libdir, libdir_suffix,
@@ -151,21 +119,23 @@ let () =
     in
     List.map add_dependencies libraries
   in
-  let runtime_launch_info =
+  let header_size, filename_mangling =
     let file = Filename.concat libdir "runtime-launch-info" in
-    read_runtime_launch_info file in
-  let header_size =
-    let {buffer; executable_offset; _} = runtime_launch_info in
-    String.length buffer - executable_offset in
+    In_channel.with_open_bin file @@ fun ic ->
+      In_channel.length ic, (input_char ic <> '\000')
+  in
   let bytecode_shebangs_by_default =
-    runtime_launch_info.launcher <> Executable in
-  let launcher_searches_for_ocamlrun = Sys.win32 in
-  let target_launcher_searches_for_ocamlrun = Sys.win32 in
+    Config.launch_method <> Config.Executable in
+  let launcher_searches_for_ocamlrun =
+    (config.has_runtime_search <> Config.Disable) in
+  let target_launcher_searches_for_ocamlrun =
+    (Config.search_method <> Config.Disable) in
   let config =
     {config with libraries;
                  launcher_searches_for_ocamlrun;
                  target_launcher_searches_for_ocamlrun;
-                 bytecode_shebangs_by_default}
+                 bytecode_shebangs_by_default;
+                 filename_mangling}
   in
   (* A compiler distribution is _Relocatable_ if its build, for a given system,
      satisfies the following three properties:
@@ -180,20 +150,31 @@ let () =
 
      For the compiler's files to be reproducible, the compiler needs to be both
      relocatable and also required support from the assembler and C compiler. *)
-  let relocatable = false in
+  let relocatable =
+    config.has_relative_libdir <> None
+    && config.has_runtime_search <> Config.Disable
+  in
   let reproducible =
     relocatable
-    (* At present, the compiler build doesn't actually take advantage of this
-       configuration, but this does not matter because the compiler cannot yet
-       be relocatable! *)
     && (not config.has_ocamlopt
         || not Toolchain.assembler_embeds_build_path
         || Config.as_has_debug_prefix_map && Config.architecture <> "riscv")
     && not Toolchain.linker_embeds_build_path
     && (not Toolchain.c_compiler_always_embeds_build_path
         || not Toolchain.c_compiler_debug_paths_can_be_absolute)
+    (* Prior to #13828 (OCaml 5.4.0), .cmt and .cmti embed the absolute location
+       of the compiler without using BUILD_PATH_PREFIX_MAP. However, this
+       embedding is not entirely predictable, because it only happens when
+       ocamlc.opt or ocamlopt.opt is used for compilation, rather than when the
+       bytecode version of the tool is passed is explicitly to ocamlrun (in this
+       case, Sys.argv.(0) always retains the relative path used in the build
+       system). For this reason, when configured relatively, on Windows, with
+       native compilation available, accept that the Build directory may appear
+       in .cmt/.cmti files, and therefore that the output may not be
+       reproducible. *)
+    && (not Sys.win32 || not config.has_ocamlopt)
   in
-  let target_relocatable = false in
+  let target_relocatable = (Config.search_method <> Config.Disable) in
   (* Use Harness.pp_path unless --verbose was specified *)
   let pp_path =
     if verbose then
@@ -255,11 +236,26 @@ let () =
                                          pp_path prefix;
     Sys.rename new_prefix prefix);
   let env =
-    make_env ~phase:Renamed ~prefix:new_prefix ~bindir_suffix ~libdir_suffix in
+    make_env ~phase:Execution ~prefix:new_prefix ~bindir_suffix ~libdir_suffix
+  in
   (* 3. Re-run the test programs compiled with the normal prefix *)
   Printf.printf "Re-running test programs\n%!";
-  List.iter
-    (function `Some f -> assert (f env = `None) | `None -> ()) programs;
+  (* Verify that the searching runtimes are searching the directory containing
+     the program itself first. *)
+  let runtime =
+    if config.filename_mangling then
+      Misc.RuntimeID.(ocamlrun "" (make_zinc ()))
+    else
+      "ocamlrun"
+  in
+  rename_exe_in_test_root env ("test-" ^ runtime) runtime;
+  Fun.protect
+    ~finally:(fun () -> rename_exe_in_test_root env runtime ("test-" ^ runtime))
+    (fun () ->
+      List.iter
+        (function `Some f -> assert (f env = `None) | `None -> ()) programs);
+  let env =
+    make_env ~phase:Renamed ~prefix:new_prefix ~bindir_suffix ~libdir_suffix in
   (* 4. Finally re-run the main test battery in the new prefix *)
   Compmisc.reinit_path ~standard_library:libdir ();
   let programs = run_tests env in
diff --git a/testsuite/tools/test_ld_conf.ml b/testsuite/tools/test_ld_conf.ml
index c866dde4ca58..9a74ae529bba 100644
--- a/testsuite/tools/test_ld_conf.ml
+++ b/testsuite/tools/test_ld_conf.ml
@@ -39,12 +39,13 @@ type ld_conf_test = {
 and var_setting = Unset | Empty | Set of string list
 
 (* Set of tests to run in a given environment *)
-let tests _config env =
+let tests config env =
   (* Convenience function - [if_ld_conf_found outcome] returns the empty list in
      the Renamed phase. *)
   let if_ld_conf_found outcome =
-    (* ocamlrun can't find ld.conf after the prefix has been renamed *)
-    if Environment.is_renamed env then
+    (* ocamlrun can only find ld.conf after the prefix has been renamed if it's
+       configured with --with-relative-libdir *)
+    if Environment.is_renamed env && config.has_relative_libdir = None then
       []
     else
       outcome
@@ -63,22 +64,29 @@ let tests _config env =
           Environment.libdir env
         else
           Config.standard_library in
+      let libdir =
+        if config.has_relative_libdir = None then
+          libdir
+        else
+          (* Unix.realpath raises Invalid_argument if it's not available *)
+          try Unix.realpath libdir
+          with Invalid_argument _ -> libdir in
       let (/) = Filename.concat in
       let data = [
         (* Root directory (both forms) preserved *)
         "/", "/", None;
         "//", "//", None;
         (* Current and Parent directory names *)
-        ".", ".", None;
-        "..", "..", None;
+        ".", libdir, None;
+        "..", libdir / "..", None;
         (* Current and Parent directory names with OS-default trailing separator
            (i.e. ./ and ../ on Unix and .\ and ..\ on Windows) *)
-        "." / "", "." / "", None;
-        ".." / "", ".." / "", None;
+        "." / "", libdir / "", None;
+        ".." / "", libdir / ".." / "", None;
         (* "stublibs" relative to the Current and Parent directory (using OS-
            default separator) *)
-        "." / "stublibs", "." / "stublibs", None;
-        ".." / "stublibs", ".." / "stublibs", None;
+        "." / "stublibs", libdir / "stublibs", None;
+        ".." / "stublibs", libdir / ".." / "stublibs", None;
         (* Other cases - implicit and absolute entries, and entries beginning
            with the Current and Parent directory names *)
         "stublibs", "stublibs", None;
@@ -88,15 +96,7 @@ let tests _config env =
         "/lib/ocaml", "/lib/ocaml", Some "/lib/ocaml\r";
       ] in
       let fold (main, main_outcome, main_outcome_cr) (line, outcome, cr) =
-        let cr = match cr with
-        | Some cr -> cr
-        | None ->
-            (* Windows opens ld.conf in text mode, so the \r are stripped *)
-            if Sys.win32 then
-              outcome
-            else
-              outcome ^ "\r"
-        in
+        let cr = Option.value ~default:outcome cr in
         line::main, outcome::main_outcome, cr::main_outcome_cr
       in
       List.fold_left fold ([], [], []) (List.rev data)
@@ -185,12 +185,12 @@ let tests _config env =
     let tests =
       (* As first, but with a CR at the end of each line *)
       let outcome =
-        (* Windows opens ld.conf in text mode, so the line with just \r is
-           read as an empty string and consequently stripped *)
+        (* Known issue: Windows strips out the blank entries in the search
+           path (somewhat counterintuitively!) *)
         if Sys.win32 then
           main_outcome_cr
         else
-          "\r" :: main_outcome_cr
+          "." :: main_outcome_cr
       in
       {base with description = "Base ld.conf with CRLF endings";
                  stdlib = List.map (Fun.flip (^) "\r") ("" :: main);
@@ -227,27 +227,28 @@ let tests _config env =
             stdlib = ["ld.conf"];
             outcome = outcome_caml_ld_library_path
                         @ if_ld_conf_found ["ld.conf"]} :: tests in
+    let ld_conf_outcome = if_ld_conf_found ["masked-stdlib"] in
     let tests =
-      (* An empty CAMLLIB should cause ld.conf in the Standard Library to be
-         ignored, but not CAML_LD_LIBRARY PATH *)
+      (* An empty CAMLLIB shouldn't hide ld.conf in the Standard Library *)
       {base with description = "Empty CAMLLIB";
                  caml_ld_library_path = Set ["env"];
                  camllib = Empty;
                  stdlib = ["masked-stdlib"];
-                 outcome = ["env"]} :: tests in
+                 outcome = "env" :: ld_conf_outcome} :: tests in
     let tests =
-      (* An empty OCAMLLIB should cause ld.conf in both the Standard Library and
-         CAMLLIB to be ignored, but not CAML_LD_LIBRARY_PATH *)
+      (* An empty OCAMLLIB shouldn't hide ld.conf in either the Standard Library
+         or CAMLLIB\ld.conf *)
       {description = "Empty OCAMLLIB";
        caml_ld_library_path = Set ["env"];
        ocamllib = Empty;
        camllib = Set ["masked-camllib"];
        stdlib = ["masked-stdlib"];
-       outcome = ["env"]} :: tests in
+       outcome = ["env"; "masked-camllib"] @ ld_conf_outcome} :: tests in
     tests
   in
   (* Batch 3: load priority, embedded NUL characters, EOL-at-EOF, etc. *)
   let tests =
+    let ld_conf_outcome = if_ld_conf_found ["libdir"] in
     let tests =
       (* OCAMLLIB should have priority over CAMLLIB and the Standard Library *)
       {description = "$OCAMLLIB/ld.conf";
@@ -255,19 +256,19 @@ let tests _config env =
        ocamllib = Set ["ocamllib\000"; "hidden"];
        camllib = Set ["camllib\000"; "hidden"];
        stdlib = ["libdir"];
-       outcome = ["env"; "ocamllib"]} :: tests in
+       outcome = ["env"; "ocamllib"; "camllib"] @ ld_conf_outcome} :: tests in
     let tests =
       (* CAMLLIB should have priority over the Standard Library *)
       {base with description = "$CAMLLIB/ld.conf";
                  caml_ld_library_path = Set ["env"];
                  camllib = Set ["camllib\000"; "hidden"];
                  stdlib = ["libdir"];
-                 outcome = ["env"; "camllib"]} :: tests in
+                 outcome = ["env"; "camllib"] @ ld_conf_outcome} :: tests in
     let tests =
       (* EOL-at-EOF should not add a blank entry to the search path *)
       {base with description = "EOF-at-EOF";
             stdlib = (if Sys.win32 then ["libdir\r\n"] else ["libdir\n"]);
-            outcome = if_ld_conf_found ["libdir"]} :: tests in
+            outcome = ld_conf_outcome} :: tests in
     tests
   in
   tests
@@ -333,8 +334,9 @@ let () =
     let runtime =
       mode = Bytecode && Harness.ocamlc_fails_after_rename config in
     (* In the Renamed phase, Config.standard_library will still point to the
-       Original location *)
-    let stdlib = true in
+       Original location, unless the compiler has been configured with a
+       relative libdir *)
+    let stdlib = (config.has_relative_libdir = None) in
     let (_, output) =
       Environment.run_process ~runtime ~stdlib env compiler args in
     Environment.display_output output;
@@ -349,104 +351,32 @@ let () =
     in
     (* In the Renamed phase, the test driver will need to be launched with
        ocamlrun, unless executables produced by the compiler are capable of
-       searching for the runtime (as the Windows executable launcher does) *)
+       searching for the runtime (as the Windows executable launcher does) or
+       the compiler has been configured with a relative libdir (as in this mode
+       the bytecode header will have the correct location) *)
     let runtime =
       mode = Bytecode
-      && not config.target_launcher_searches_for_ocamlrun in
+      && not config.target_launcher_searches_for_ocamlrun
+      && config.has_relative_libdir = None in
     let run run_process test =
       let code, lines =
         run_process ?argv0:None ~runtime test_program []
       in
       if code = 0 then
         let lines =
-          (* Known issue: Sys.getenv processes blank environment variables
-             differently from _wgetenv which in the tests will cause it load
-             ld.conf files. The tests have been written to allow for this by
-             having the lines which are _not_ expected to appear on Unix be
-             prefixed with "masked-". *)
-          if Sys.win32 then
-            if ((test.camllib = Empty
-                   && not (Environment.is_renamed env))
-                || test.ocamllib = Empty) then
-              let unmask s = not (String.starts_with ~prefix:"masked-" s) in
-              let lines' = List.filter unmask lines in
-              (* If Windows behaviour has been harmonised, then the filtered
-                 list of lines would be the same as the unfiltered list. If this
-                 happens, insert an extra line to "poison" the test output to
-                 prevent this behaviour from being silently fixed. *)
-              if lines = lines' then
-                "poisoned"::lines
-              else
-                lines'
-            else
-              lines
-          else
-            lines
-        in
-        let lines =
-          (* Known issue: ocamlc opens ld.conf in text mode on Cygwin but
-             ocamlrun opens it in binary mode (the default). This means that
-             ocamlrun will return lines ending with \r, but ocamlc will both
-             strip the \r and ignore a line consisting of just \r (because that
-             appears blank in text mode). This is mitigated by ensuring that the
-             \r line is always first in the test, and then adding back the \r to
-             the output on Cygwin. This will clearly fail if the behaviour of
-             ocamlrun and ocamlc is harmonised. *)
-          match test.stdlib with
-          | "\r" :: _ when Sys.cygwin && lines <> [] ->
-              "\r" :: List.map (Fun.flip (^) "\r") (List.tl lines)
-          | _ ->
-              lines
-        in
-        let lines =
-          (* Known issue: Misc.split_path_contents ignores empty strings where
-             caml_decompose_path does not. Mitigate it by detecting the
-             environment setting and simulating the line. *)
-          if test.caml_ld_library_path = Set []
-             || test.caml_ld_library_path = Empty then
+          (* Known issues:
+             - Misc.split_path_contents ignores empty strings where
+               caml_decompose_path does not
+             - Sys.getenv can't return empty environment variables on Windows,
+               but _wgetenv can
+             - Windows strips out the blank entries in the search path
+               (somewhat counterintuitively!) *)
+          if not Sys.win32 && (test.caml_ld_library_path = Set []
+                               || test.caml_ld_library_path = Empty) then
             "." :: lines
           else
             lines
         in
-        (* Known issue: Windows strips out the blank entries in the search path
-           (somewhat counterintuitively!) *)
-        let lines =
-          if not Sys.win32 then
-            lines
-          else
-            List.drop_while (String.equal ".") lines
-        in
-        let lines =
-          (* Known issue: Dll.ld_conf_contents preserves NUL characters in lines
-             where caml_parse_ld_conf terminates processing. This is mitigated
-             in the test by putting a single line "hidden" after the line with
-             an embedded NUL. *)
-          let includes_nulls =
-            let includes_nulls = function
-            | Unset | Empty -> false
-            | Set l -> List.exists (Fun.flip String.contains '\000') l
-            in
-            includes_nulls test.ocamllib || includes_nulls test.camllib
-          in
-          if includes_nulls then
-            let strip_null s =
-              match String.index s '\000' with
-              | index ->
-                  String.sub s 0 index
-              | exception Not_found ->
-                  s
-            in
-            let lines' = List.map strip_null lines in
-            if lines <> lines' then
-              List.filter ((<>) "hidden") lines'
-            else
-              (* As with empty environment variables above, if this behaviour
-                 appears to have been fixed, poison the output of the test so
-                 that doesn't happen silently. *)
-              "poisoned" :: lines
-          else
-            lines
-        in
         description :: lines
       else
         Harness.fail_because "%s is expected to exit with code 0"
diff --git a/testsuite/tools/toolchain.ml.in b/testsuite/tools/toolchain.ml.in
index e976fe59b46a..7c8e7a456269 100644
--- a/testsuite/tools/toolchain.ml.in
+++ b/testsuite/tools/toolchain.ml.in
@@ -15,7 +15,7 @@
 open Harness.Import
 
 let c_compiler_vendor = {@QS@|@ocaml_cc_vendor@|@QS@}
-let compression_c_libraries = {@QS@|@zstd_libs@|@QS@}
+let as_is_cc = @as_is_cc@
 
 (* cf. OCAML_CC_VENDOR in aclocal.m4 and utils.config.mli *)
 let is_clang =
diff --git a/testsuite/tools/toolchain.mli b/testsuite/tools/toolchain.mli
index ca5a71948cfa..625bdf5057c4 100644
--- a/testsuite/tools/toolchain.mli
+++ b/testsuite/tools/toolchain.mli
@@ -50,5 +50,6 @@ val c_compiler_vendor : string
 (** The vendor and version of the C compiler, as determined by configure.ac
     (see Config.c_compiler_vendor in OCaml 5.5) *)
 
-val compression_c_libraries : string
-(** The C libraries needed with -lcomprmarsh *)
+val as_is_cc : bool
+(** Whether the assembler is actually an assembler, or whether we are really
+    assembling files via the C compiler (see Config.as_is_cc in OCaml 5.5) *)
diff --git a/tools/byterntm.mli b/tools/byterntm.mli
new file mode 100644
index 000000000000..4a9c206c4eed
--- /dev/null
+++ b/tools/byterntm.mli
@@ -0,0 +1,33 @@
+(**************************************************************************)
+(*                                                                        *)
+(*                                 OCaml                                  *)
+(*                                                                        *)
+(*            David Allsopp, University of Cambridge & Tarides            *)
+(*                                                                        *)
+(*   Copyright 2025 David Allsopp Ltd.                                    *)
+(*                                                                        *)
+(*   All rights reserved.  This file is distributed under the terms of    *)
+(*   the GNU Lesser General Public License version 2.1, with the          *)
+(*   special exception on linking described in the file LICENSE.          *)
+(*                                                                        *)
+(**************************************************************************)
+
+(** Parser for RNTM in bytecode executables. Parses both the RNTM section and
+    the shebang launcher produced by {!Bytelink}. *)
+
+(** Search methods used by a tendered bytecode image to find a runtime. *)
+type search_method =
+| Disable of string
+    (** Check fixed location only *)
+| Fallback of string
+    (** Check given location first then fallback to searching for the
+        interpreter *)
+| Enable
+    (** Always search for the interpreter *)
+
+val read_runtime :
+  Bytesections.section_table -> in_channel
+  -> (string * Misc.RuntimeID.t option * search_method) option
+(** Returns the runtime used by this tendered/standalone image. If the runtime
+    used cannot be parsed, or the image was linked using -without-runtime, then
+    [None] is returned. *)
diff --git a/tools/byterntm.mll b/tools/byterntm.mll
new file mode 100644
index 000000000000..43b43c1806b1
--- /dev/null
+++ b/tools/byterntm.mll
@@ -0,0 +1,123 @@
+(**************************************************************************)
+(*                                                                        *)
+(*                                 OCaml                                  *)
+(*                                                                        *)
+(*            David Allsopp, University of Cambridge & Tarides            *)
+(*                                                                        *)
+(*   Copyright 2025 David Allsopp Ltd.                                    *)
+(*                                                                        *)
+(*   All rights reserved.  This file is distributed under the terms of    *)
+(*   the GNU Lesser General Public License version 2.1, with the          *)
+(*   special exception on linking described in the file LICENSE.          *)
+(*                                                                        *)
+(**************************************************************************)
+
+{
+type search_method =
+| Disable of string
+| Fallback of string
+| Enable
+
+(* First word of the current line being analysed - [exec ...], [r=...], or
+   [c=...] *)
+type state = Exec | R | C of string
+
+let cut_runtime_id search name =
+  let len = String.length name in
+  let id =
+    if len < 6 || name.[len - 5] <> '-' then
+      None
+    else
+      Misc.RuntimeID.of_string (String.sub name (len - 4) 4)
+  in
+  let name =
+    if id = None then
+      name
+    else
+      String.sub name 0 (len - 5)
+  in
+  Some (name, id, search)
+}
+
+rule analyze = parse
+(* RNTM section for -runtime-search absolute or shebang directly to the
+   runtime *)
+  | "#!" ([^ ' ' '\n']* as dir) ('/' as sep) ([^ '/' ' ' '\n']+ as runtime) '\n'
+  | ([^ '\000']* as dir) (['/' '\\' '\000'] as sep) (* Directory portion *)
+    ([^ '\\' '/' '\000']+ as runtime) eof           (* Runtime portion *)
+      { if sep = '\000' then
+          if dir = "" then
+            cut_runtime_id Enable runtime
+          else
+            let dir = Filename.concat dir "" in
+            cut_runtime_id (Fallback dir) runtime
+        else
+          let dir = dir ^ String.make 1 sep in
+          cut_runtime_id (Disable dir) runtime }
+
+(* Shell script launcher (if it matches, this always matches more than the above
+   regexp) *)
+  | "#!" [^ ' ' '\n']+ "/sh\n" (("exec '" | "r='") as next)
+      { let state = if next.[0] = 'r' then R else Exec in
+        analyze_sh_launcher state (Buffer.create 1024) lexbuf }
+
+  | _ | eof
+      { None }
+
+and analyze_sh_launcher state b = parse
+(* An embedded single quote *)
+  | "'\\''"
+      { analyze_sh_launcher state (Buffer.add_char b '\''; b) lexbuf }
+
+  | [^ '\'' ]+ as s
+      { analyze_sh_launcher state (Buffer.add_string b s; b) lexbuf }
+
+(* exec line for -runtime-search disable *)
+  | "' \"$0\" \"$@\"\n"
+      { if state = Exec then
+          let name = Buffer.contents b in
+          let runtime = Filename.basename name in
+          let dir =
+            String.sub name 0 (String.length name - String.length runtime)
+          in
+          cut_runtime_id (Disable dir) runtime
+        else
+          None }
+
+(* r= line for -runtime-search {fallback,enable} *)
+  | "'\n" ("c='" as c)?
+      { if state = R then
+          let runtime = Buffer.contents b in
+          if c = None then
+            cut_runtime_id Enable runtime
+          else
+            analyze_sh_launcher (C runtime) (Buffer.clear b; b) lexbuf
+        else
+          None }
+
+(* c= line for -runtime-search fallback *)
+  | "'\"$r\"\n"
+      { match state with
+        | C runtime ->
+            cut_runtime_id (Fallback (Buffer.contents b)) runtime
+        | _ ->
+            None }
+
+  | _ | eof
+      { None }
+
+{
+let read_runtime t ic =
+  seek_in ic 0;
+  let lexbuf =
+    try
+      if really_input_string ic 2 = "#!" then
+        let () = seek_in ic 0 in
+        Some (Lexing.from_channel ic)
+      else
+        let rntm = Bytesections.(read_section_string t ic Name.RNTM) in
+        Some (Lexing.from_string rntm)
+    with End_of_file | Not_found -> None
+  in
+  Option.bind lexbuf analyze
+}
diff --git a/tools/ci/actions/runner.sh b/tools/ci/actions/runner.sh
index 512e57d23829..05805ae7e20c 100755
--- a/tools/ci/actions/runner.sh
+++ b/tools/ci/actions/runner.sh
@@ -16,7 +16,8 @@
 
 set -xe
 
-PREFIX=~/local
+# The prefix is designed to be usable as an opam local switch
+PREFIX=~/local/_opam
 
 MAKE="make $MAKE_ARG"
 SHELL=dash
@@ -56,11 +57,12 @@ EOF
   # $CONFIG_ARG also appears last to allow settings specified here to be
   # overridden by the workflows.
   call-configure --prefix="$PREFIX" \
+                 --docdir="$PREFIX/doc/ocaml" \
                  --enable-flambda-invariants \
                  --enable-ocamltest \
                  --enable-native-toplevel \
                  --disable-dependency-generation \
-                 $CONFIG_ARG
+                 -C $CONFIG_ARG
 }
 
 Build () {
@@ -125,13 +127,116 @@ API_Docs () {
 }
 
 Install () {
-  $MAKE install
+  $MAKE INSTALL_MODE=list install | grep '^->' | sort | uniq -d > duplicates
+  if [ -s duplicates ]; then
+    echo "The installation duplicates targets:"
+    cat duplicates
+    exit 1
+  fi
+  rm duplicates
+  $MAKE DESTDIR="$PWD/install" install
+  find $PWD/install -name _opam -type d
+  $MAKE INSTALL_MODE=clone install
+  ret="$PWD"
+  script="$PWD/ocaml-compiler-clone.sh"
+  cd "$(find $PWD/install -name _opam -type d)"
+  mkdir -p "share/ocaml"
+  cp "$ret/config.status" "$ret/config.cache" "share/ocaml"
+  cp "$ret/ocaml-compiler-clone.sh" "share/ocaml/clone"
+  sh $script "$PWD" ~/local/_opam
+  cd "$ret"
+  rm -rf install
+  rm ocaml-compiler-clone.sh
 }
 
+target_libdir_is_relative='^ *TARGET_LIBDIR_IS_RELATIVE *= *false'
+
 Test-In-Prefix () {
+  { set +x
+    echo 'Checking that compilers invoked with alternate runtimes use their'
+    echo "configured location, not the alternate runtime's"
+    expected1="$(realpath "$PREFIX/lib/ocaml")"
+  } 2>/dev/null
+  if [[ ! -d "$PREFIX.new" ]]; then
+    # In Re-Test-In-Prefix, $PREFIX is the original compiler built by the
+    # workflow and then $PREFIX.new is the "alternate configuration". The first
+    # time round, we clone whichever compiler has just been built for this test.
+    cp -a "$PREFIX" "$PREFIX.new"
+    remove="$PREFIX.new"
+    if grep -q "$target_libdir_is_relative" Makefile.build_config; then
+      # Compiler configured absolutely - both should return the same answer
+      expected2="$expected1"
+    else
+      # Compiler configured relatively
+      expected2="$(realpath "$PREFIX").new/lib/ocaml"
+    fi
+  else
+    # The alternate configuration path should be returned, regardless of whether
+    # the runtime invoking it is an absolute or a relative one from another
+    # location.
+    expected2="$(realpath "$PREFIX").new/lib/ocaml-lib"
+    remove=''
+  fi
+  { set +x
+    lib1="$($PREFIX.new/bin/ocamlrun $PREFIX/bin/ocamlc.byte -where)"
+    lib2="$($PREFIX/bin/ocamlrun $PREFIX.new/bin/ocamlc.byte -where)"
+    echo "$PREFIX/bin/ocamlc.byte OSLD: $($PREFIX/bin/ocamlrun \
+      $PREFIX/bin/ocamlobjinfo.byte $PREFIX/bin/ocamlc.byte \
+        | sed -ne 's/^caml_standard_library_default: //p')"
+    echo -n "$PREFIX.new/bin/ocamlrun standard_library_default: "
+    $PREFIX.new/bin/ocamlrun -config | sed -ne 's/standard_library_default: //p'
+    echo "$PREFIX.new/bin/ocamlrun $PREFIX/bin/ocamlc.byte -where: $lib1"
+    if [[ $lib1 != $expected1 ]]; then
+      echo -e '  \e[31mEXPECTED\e[0m:' "$expected1"
+    fi
+    echo
+    echo "$PREFIX.new/bin/ocamlc.byte OSLD: $($PREFIX.new/bin/ocamlrun \
+      $PREFIX.new/bin/ocamlobjinfo.byte $PREFIX.new/bin/ocamlc.byte \
+        | sed -ne 's/^caml_standard_library_default: //p')"
+    echo -n "$PREFIX/bin/ocamlrun standard_library_default: "
+    $PREFIX/bin/ocamlrun -config | sed -ne 's/standard_library_default: //p'
+    echo "$PREFIX/bin/ocamlrun $PREFIX.new/bin/ocamlc.byte -where: $lib2"
+    if [[ $lib2 != $expected2 ]]; then
+      echo -e '  \e[31mEXPECTED\e[0m:' "$expected2"
+    fi
+    [[ $lib1 = $expected1 && $lib2 = $expected2 ]] && echo 'Correct.' || exit 1
+  } 2>/dev/null
+  [[ -z $remove ]] || rm -rf "$remove"
   $MAKE -C testsuite/in_prefix -f Makefile.test test-in-prefix
 }
 
+Re-Test-In-Prefix () {
+  mkdir -p bak
+  mv Makefile.config Makefile.build_config config.status bak
+  git clean -dfX &>/dev/null
+  mv bak/Makefile.config bak/Makefile.build_config bak/config.status .
+  rmdir bak
+  # The libdir is configured to be $PREFIX.new/lib/ocaml-lib in order to
+  # "poison" the cross-runtime test (otherwise if $PREFIX/bin/ocamlc.byte is
+  # missing OSLD, then $PREFIX.new/bin/ocamlrun would still supply the correct
+  # ../lib/ocaml. This way, it supplies ../lib/ocaml-lib and the test correctly
+  # fails)
+  if grep -q "$target_libdir_is_relative" Makefile.build_config; then
+    # Compiler configured absolutely - reconfigure relatively
+    echo '::group::Re-building the compiler with a relative libdir'
+    $MAKE COMPUTE_DEPS=false reconfigure \
+          'ADDITIONAL_CONFIGURE_ARGS=--with-relative-libdir=../lib/ocaml-lib \
+--enable-runtime-search --enable-runtime-search-target=fallback \
+--prefix='"$PREFIX"'.new'
+  else
+    # Compiler configured relatively - reconfigure absolutely
+    echo '::group::Re-building the compiler with an absolute libdir'
+    $MAKE COMPUTE_DEPS=false reconfigure \
+          'ADDITIONAL_CONFIGURE_ARGS=--without-relative-libdir \
+--disable-runtime-search --disable-runtime-search-target \
+--prefix='"$PREFIX"'.new --libdir='"$PREFIX"'.new/lib/ocaml-lib'
+  fi
+  $MAKE
+  $MAKE install
+  echo '::endgroup::'
+  Test-In-Prefix
+}
+
 Checks () {
   if fgrep 'SUPPORTS_SHARED_LIBRARIES=true' Makefile.config &>/dev/null ; then
     echo Check the code examples in the manual
@@ -141,7 +246,7 @@ Checks () {
   # we would need to redo (small parts of) world.opt afterwards to
   # use the compiler again
   $MAKE check_all_arches
-  # Ensure that .gitignore is up-to-date - this will fail if any untreacked or
+  # Ensure that .gitignore is up-to-date - this will fail if any untracked or
   # altered files exist.
   test -z "$(git status --porcelain)"
   # check that the 'clean' target also works
@@ -150,7 +255,9 @@ Checks () {
   $MAKE -C manual distclean
   # check that the `distclean` target definitely cleans the tree
   $MAKE distclean
-  # Check the working tree is clean
+  # Check the working tree is clean - config.cache is intentionally not deleted
+  # by any of the clean targets
+  rm config.cache
   test -z "$(git status --porcelain)"
   # Check that there are no ignored files
   test -z "$(git ls-files --others -i --exclude-standard)"
@@ -214,6 +321,24 @@ BasicCompiler () {
   ReportBuildStatus 0
 }
 
+CreateSwitch () {
+  # This can be switched to use the Ubuntu package when Ubuntu 26.04 is deployed
+  # (opam 2.1.5 in Ubuntu 24.04 is too old)
+  curl -Lo opam \
+ 'https://github.com/ocaml/opam/releases/download/2.4.1/opam-2.4.1-x86_64-linux'
+  chmod +x opam
+  ./opam init --cli=2.4 --bare --disable-sandboxing --yes --auto-setup
+  # This is intentionally done before the switch is created - if the install
+  # target creates _opam then the switch creation will fail.
+  $MAKE INSTALL_MODE=opam OPAM_PACKAGE_NAME=ocaml-variants install
+  # These commands intentionally run using opam's "default" CLI
+  ./opam switch create ~/local --empty
+  ./opam switch --switch ~/local set-invariant --no-action ocaml-option-flambda
+  ./opam pin add --switch ~/local --no-action --kind=path ocaml-variants .
+  ./opam install --switch ~/local --yes --assume-built ocaml-variants
+  ./opam exec --switch ~/local -- ocamlopt -v
+}
+
 case $1 in
 configure) Configure;;
 build) Build;;
@@ -223,9 +348,11 @@ test_prefix) TestPrefix $2;;
 api-docs) API_Docs;;
 install) Install;;
 test-in-prefix) Test-In-Prefix;;
+re-test-in-prefix) Re-Test-In-Prefix;;
 manual) BuildManual;;
 other-checks) Checks;;
 basic-compiler) BasicCompiler;;
+opam) CreateSwitch;;
 *) echo "Unknown CI instruction: $1"
    exit 1;;
 esac
diff --git a/tools/ci/appveyor/appveyor_build.cmd b/tools/ci/appveyor/appveyor_build.cmd
index 5f18b1cffed2..aaf6f929791a 100644
--- a/tools/ci/appveyor/appveyor_build.cmd
+++ b/tools/ci/appveyor/appveyor_build.cmd
@@ -22,7 +22,7 @@
 
 chcp 65001 > nul
 set BUILD_PREFIX=🐫реализация
-set OCAMLROOT=%PROGRAMFILES%\Бактріан🐫
+set OCAMLROOT=C:\Бактріан🐫
 
 if "%1" neq "install" goto %1
 setlocal enabledelayedexpansion
@@ -69,7 +69,13 @@ if %CYGWIN_UPGRADE_REQUIRED% equ 1 (
   )
 )
 if "%CYGWIN_INSTALL_PACKAGES%" neq "" "%CYG_ROOT%\setup-x86_64.exe" --quiet-mode --no-shortcuts --no-startmenu --no-desktop --only-site --root "%CYG_ROOT%" --site "%CYG_MIRROR%" --local-package-dir "%CYG_CACHE%" %CYGWIN_FLAGS% --packages %CYGWIN_INSTALL_PACKAGES:~1%
-for %%P in (%CYGWIN_COMMANDS%) do "%CYG_ROOT%\bin\%%P.exe" --version 2> nul > nul || set CYGWIN_UPGRADE_REQUIRED=1
+for %%P in (%CYGWIN_COMMANDS%) do (
+  if %%P equ unzip (
+    "%CYG_ROOT%\bin\%%P.exe" -v 2> nul > nul || set CYGWIN_UPGRADE_REQUIRED=1
+  ) else (
+    "%CYG_ROOT%\bin\%%P.exe" --version 2> nul > nul || set CYGWIN_UPGRADE_REQUIRED=1
+  )
+)
 "%CYG_ROOT%\bin\bash.exe" -lc "cygcheck -dc %CYGWIN_PACKAGES%"
 if %CYGWIN_UPGRADE_REQUIRED% equ 1 (
   echo Cygwin package upgrade required - please go and drink coffee
@@ -87,6 +93,11 @@ if not defined SDK (
   if "%PORT%" equ "mingw32" set SDK=call "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars32.bat"
 )
 %SDK%
+rem The environment block becomes very large on AppVeyor, which can cause
+rem problems for xargs in Cygwin. These two environment variables from the SDK
+rem infrastructure can be safely junked to reduce the size of the block.
+set __VSCMD_PREINIT_PATH=
+set EXTERNAL_INCLUDE=
 goto :EOF
 
 :install
@@ -103,6 +114,9 @@ if "%BOOTSTRAP_FLEXDLL%" equ "true" (
 cd "%APPVEYOR_BUILD_FOLDER%"
 appveyor DownloadFile "https://github.com/ocaml/flexdll/archive/%FLEXDLL_VERSION%.tar.gz" -FileName "flexdll.tar.gz" || exit /b 1
 appveyor DownloadFile "https://github.com/ocaml/flexdll/releases/download/%FLEXDLL_VERSION%/flexdll-bin-%FLEXDLL_VERSION%.zip" -FileName "flexdll.zip" || exit /b 1
+appveyor DownloadFile "https://github.com/ocaml/opam/releases/download/2.4.1/opam-2.4.1-x86_64-windows.exe" -FileName "opam.exe" || exit /b 1
+md "%PROGRAMFILES%\flexdll"
+move opam.exe "%PROGRAMFILES%\flexdll"
 rem flexdll.zip is processed here, rather than in appveyor_build.sh because the
 rem unzip command comes from MSYS2 (via Git for Windows) and it has to be
 rem invoked via cmd /c in a bash script which is weird(er).
@@ -115,8 +129,8 @@ rem in the list just so that the Cygwin version is always displayed on the log).
 rem CYGWIN_COMMANDS is a corresponding command to run with --version to test
 rem whether the package works. This is used to verify whether the installation
 rem needs upgrading.
-set CYGWIN_PACKAGES=cygwin make diffutils
-set CYGWIN_COMMANDS=cygcheck make diff
+set CYGWIN_PACKAGES=cygwin make diffutils unzip
+set CYGWIN_COMMANDS=cygcheck make diff unzip
 if "%PORT%" equ "mingw32" (
   rem mingw64-i686-runtime does not need explicitly installing, but it's useful
   rem to have the version reported.
diff --git a/tools/ci/appveyor/appveyor_build.sh b/tools/ci/appveyor/appveyor_build.sh
index 5d29916eaf9d..3d0f21981996 100755
--- a/tools/ci/appveyor/appveyor_build.sh
+++ b/tools/ci/appveyor/appveyor_build.sh
@@ -70,7 +70,10 @@ function set_configuration {
   CACHE_FILE_PREFIX="$CACHE_DIRECTORY/config.cache-$1"
   CACHE_FILE="$CACHE_FILE_PREFIX-$CACHE_KEY"
 
-  args=('--cache-file' "$CACHE_FILE" '--prefix' "$2" '--enable-ocamltest')
+  args=('--cache-file' "$CACHE_FILE" \
+        '--prefix' "$2/_opam" \
+        '--docdir' "$2/_opam/doc/ocaml" \
+        '--enable-ocamltest')
 
   case "$1" in
     cygwin*)
@@ -87,6 +90,10 @@ function set_configuration {
       args+=('--host=x86_64-pc-windows' '--enable-dependency-generation' \
              '--enable-native-toplevel');;
   esac
+  if [[ $RELOCATABLE = 'true' ]]; then
+    args+=('--with-relative-libdir' \
+           '--enable-runtime-search' '--enable-runtime-search-target=fallback')
+  fi
 
   # Remove old configure cache if the configure script or the OS
   # have changed
@@ -103,6 +110,8 @@ function set_configuration {
     if ((failed)) ; then cat config.log ; exit $failed ; fi
   fi
 
+  cp "$CACHE_FILE" config.cache
+
 #  FILE=$(pwd | cygpath -f - -m)/Makefile.config
 #  run "Content of $FILE" cat Makefile.config
 }
@@ -110,7 +119,7 @@ function set_configuration {
 PARALLEL_URL='https://git.savannah.gnu.org/cgit/parallel.git/plain/src/parallel'
 APPVEYOR_BUILD_FOLDER=$(echo "$APPVEYOR_BUILD_FOLDER" | cygpath -f -)
 FLEXDLLROOT="$PROGRAMFILES/flexdll"
-OCAMLROOT=$(echo "$OCAMLROOT" | cygpath -f - -m)
+export OPAMSWITCH="$OCAMLROOT"
 
 if [[ $BOOTSTRAP_FLEXDLL = 'false' ]] ; then
   case "$PORT" in
@@ -195,6 +204,39 @@ case "$1" in
           make -C "$FULL_BUILD_PREFIX-$PORT/testsuite" SHOW_TIMINGS=1 all
     fi
     run "install $PORT" $MAKE -C "$FULL_BUILD_PREFIX-$PORT" install
+    make -C "$FULL_BUILD_PREFIX-$PORT" INSTALL_MODE=clone install
+    (
+      cd "$OCAMLROOT"
+      mv _opam destdir
+      #ret="$PWD"
+      #script="$PWD/ocaml-compiler-clone.sh"
+      #cd "$(find $PWD/install -name _opam -type d)"
+      mkdir -p "destdir/share/ocaml"
+      cp "$FULL_BUILD_PREFIX-$PORT/config."{cache,status} 'destdir/share/ocaml/'
+      cp "$FULL_BUILD_PREFIX-$PORT/ocaml-compiler-clone.sh" \
+           'destdir/share/ocaml/clone'
+      cd destdir
+      sh "$FULL_BUILD_PREFIX-$PORT/ocaml-compiler-clone.sh" "$PWD" \
+                                                            "$OCAMLROOT/_opam"
+    )
+    rm -rf "$OCAMLROOT"
+    $MAKE -C "$FULL_BUILD_PREFIX-$PORT" OPAM_PACKAGE_NAME=ocaml-variants \
+      INSTALL_MODE=opam install
+    (
+      cd "$FULL_BUILD_PREFIX-$PORT"
+      export PATH="$FLEXDLLROOT:$PATH"
+      opam init --cli=2.4 --bare --yes --disable-sandboxing --auto-setup \
+                --cygwin-local-install
+      # These commands intentionally run using opam's "default" CLI
+      opam switch create "$OPAMSWITCH" --empty
+      opam pin add --no-action --kind=path ocaml-variants .
+      opam pin add --no-action flexdll flexdll
+      opam install --yes flexdll winpthreads
+      opam install --yes --assume-built ocaml-variants
+      git checkout -- ocaml-variants.install
+      rm -f config.cache ocaml-variants-fixup.sh ocaml-compiler-clone.sh
+      opam exec -- ocamlc -v
+    )
     run "test $PORT in prefix" \
       $MAKE -f Makefile.test -C "$FULL_BUILD_PREFIX-$PORT/testsuite/in_prefix" \
             test-in-prefix
diff --git a/tools/objinfo.ml b/tools/objinfo.ml
index 83e36593141b..8096e581cac7 100644
--- a/tools/objinfo.ml
+++ b/tools/objinfo.ml
@@ -35,6 +35,8 @@ let uid_deps = ref false
 
 module Magic_number = Misc.Magic_number
 
+let yesno_of_bool oc b = output_string oc (if b then "YES" else "no")
+
 let dummy_crc = String.make 32 '-'
 let null_crc = String.make 32 '0'
 
@@ -67,13 +69,19 @@ let print_cmo_infos cu =
         printf "YES\n";
         printf "Primitives declared in this module:\n";
         List.iter print_line l);
-  printf "Force link: %s\n" (if cu.cu_force_link then "YES" else "no")
+  printf "Force link: %a\n" yesno_of_bool cu.cu_force_link
 
 let print_spaced_string s =
   printf " %s" s
 
-let print_cma_infos (lib : Cmo_format.library) =
-  printf "Force custom: %s\n" (if lib.lib_custom then "YES" else "no");
+let dllib (suffixed, name) =
+  if suffixed then
+    Printf.sprintf "%s-<target>-<bytecode-runtime-id>" name
+  else
+    name
+
+let print_cma_infos (lib : Cmo_format.library) lib_dllibs =
+  printf "Force custom: %a\n" yesno_of_bool lib.lib_custom;
   printf "Extra C object files:";
   (* PR#4949: print in linking order *)
   List.iter print_spaced_string (List.rev lib.lib_ccobjs);
@@ -81,7 +89,7 @@ let print_cma_infos (lib : Cmo_format.library) =
   List.iter print_spaced_string (List.rev lib.lib_ccopts);
   printf "\n";
   print_string "Extra dynamically-loaded libraries:";
-  List.iter print_spaced_string (List.rev lib.lib_dllibs);
+  List.iter print_spaced_string (List.rev_map dllib lib_dllibs);
   printf "\n";
   List.iter print_cmo_infos lib.lib_units
 
@@ -249,11 +257,14 @@ let print_cmx_infos (ui, crc) =
   printf "Currying functions:%a\n" pr_funs ui.ui_curry_fun;
   printf "Apply functions:%a\n" pr_funs ui.ui_apply_fun;
   printf "Send functions:%a\n" pr_funs ui.ui_send_fun;
-  printf "Force link: %s\n" (if ui.ui_force_link then "YES" else "no");
+  printf "Force link: %a\n" yesno_of_bool ui.ui_force_link;
   printf "For pack: %s\n"
     (match ui.ui_for_pack with
      | None -> "no"
-     | Some pack -> "YES: " ^ pack)
+     | Some pack -> "YES: " ^ pack);
+  printf
+    "Requires caml_standard_library_nat: %a\n"
+    yesno_of_bool (Compilenv.needs_stdlib_location ui)
 
 let print_cmxa_infos (lib : Cmx_format.library_infos) =
   printf "Extra C object files:";
@@ -288,9 +299,57 @@ let p_list title print = function
       p_title title;
       List.iter print l
 
+let p_runtime_id ({Misc.RuntimeID.dev; release; no_flat_float_array; fp; tsan;
+                   int31; static; no_compression; ansi; reserved} as t) =
+  let version =
+    if release > Config.release_number then
+      ""
+    else
+      if release = 0 then
+        " (Objective Caml 3.12)"
+      else if release < 16 then
+        Printf.sprintf " (OCaml 4.%02d)" (release - 1)
+      else
+        Printf.sprintf " (OCaml 5.%d)" (release - 16)
+  in
+  printf "\t%s = Release %d%s%s\n"
+    (Misc.RuntimeID.to_string t)
+    release version (if dev then " - development/altered version" else "");
+  if reserved > 0 then
+    printf "\t  - %d reserved header bit%s\n"
+      reserved (if reserved = 1 then "" else "s");
+  if no_flat_float_array then
+    printf "\t  - Flat float array representation disabled\n";
+  if fp then
+    printf "\t  - Frame pointers enabled\n";
+  if tsan then
+    printf "\t  - TSAN enabled\n";
+  if int31 then
+    printf "\t  - Compiled without 64-bit support\n";
+  if static then
+    printf "\t  - Compiled without support dynamic loading\n";
+  if no_compression then
+    printf "\t  - Compiled without support for compressed marshalling\n";
+  if ansi then
+    printf "\t  - Windows Unicode support disabled\n"
+
+let p_runtime (runtime, id, search) =
+  let runtime =
+    let some id = runtime ^ "-" ^ Misc.RuntimeID.to_string id in
+    Option.fold ~none:runtime ~some id
+  in
+  let runtime =
+    match search with
+    | Byterntm.Enable -> runtime
+    | Byterntm.Disable dir -> dir ^ runtime
+    | Byterntm.Fallback dir -> Printf.sprintf "[%s]%s" dir runtime
+  in
+  printf "Runtime:\n\t%s\n" runtime;
+  Option.iter p_runtime_id id
+
 let dump_byte ic =
   let toc = Bytesections.read_toc ic in
-  let all = Bytesections.all toc in
+  Option.iter p_runtime (Byterntm.read_runtime toc ic);
   List.iter
     (fun {Bytesections.name = section; len; _} ->
        try
@@ -317,10 +376,15 @@ let dump_byte ic =
            | SYMB ->
                let symb = Bytesections.read_section_struct toc ic section in
                print_global_table symb
+           | OSLD ->
+               let caml_standard_library_default =
+                 Bytesections.read_section_string toc ic section in
+               printf "caml_standard_library_default: %s\n"
+                      caml_standard_library_default
            | _ -> ()
        with _ -> ()
     )
-    all
+    (Bytesections.all toc)
 
 let find_dyn_offset filename =
   match Binutils.read filename with
@@ -361,8 +425,9 @@ let dump_obj_by_kind filename ic obj_kind =
        let toc_pos = input_binary_int ic in
        seek_in ic toc_pos;
        let toc = (input_value ic : library) in
+       let lib_dllibs = Dll.read_suffixed_dllibs_from_channel ic toc in
        close_in ic;
-       print_cma_infos toc
+       print_cma_infos toc lib_dllibs
     | Cmi | Cmt ->
        close_in ic;
        let cmi, cmt = Cmt_format.read filename in
diff --git a/tools/ocamlmklib.ml b/tools/ocamlmklib.ml
index f6b2a2d16ec9..398d62e6ba64 100644
--- a/tools/ocamlmklib.ml
+++ b/tools/ocamlmklib.ml
@@ -25,10 +25,8 @@ let mklib out files opts =
   Printf.sprintf "link -lib -nologo %s-out:%s %s %s" machine out opts files
   else Printf.sprintf "%s rcs %s %s %s" Config.ar out opts files
 
-(* PR#4783: under Windows, don't use absolute paths because we do
-   not know where the binary distribution will be installed. *)
 let compiler_path name =
-  if Sys.os_type = "Win32" then name else Filename.concat Config.bindir name
+  Filename.concat Config.bindir name
 
 let bytecode_objs = ref []  (* .cmo,.cma,.ml,.mli files to pass to ocamlc *)
 and native_objs = ref []    (* .cmx,.ml,.mli files to pass to ocamlopt *)
@@ -51,6 +49,7 @@ and output_c = ref ""       (* Output name for C part of library *)
 and rpath = ref []          (* rpath options *)
 and debug = ref false       (* -g option *)
 and verbose = ref false
+and suffixed = ref false    (* -suffixed option *)
 
 let starts_with s pref =
   String.length s >= String.length pref &&
@@ -164,6 +163,10 @@ let parse_arguments argv =
       c_opts := s :: !c_opts
     else if s = "-framework" then
       (let a = next_arg s in c_opts := a :: s :: !c_opts)
+    else if s = "-suffixed" then
+      suffixed := true
+    else if s = "-no-suffixed" then
+      suffixed := false
     else if starts_with s "-" then
       prerr_endline ("Unknown option " ^ s)
     else
@@ -210,6 +213,9 @@ Options are:
   -oc <name>     Generated C library is named dll<name>.so or lib<name>.a
   -rpath <dir>   Same as -dllpath <dir>
   -R<dir>        Same as -rpath
+  -suffixed      Append runtime ID to any generated shared libraries
+  -no-suffixed   Do not append runtime ID to any generated shared libraries
+                 (default)
   -verbose       Print commands before executing them
   -v             same as -verbose
   -version       Print version and exit
@@ -286,11 +292,17 @@ let flexdll_dirs =
 let build_libs () =
   if !c_objs <> [] then begin
     if !dynlink then begin
+      let dllname =
+        if !suffixed then
+          Misc.RuntimeID.stubslib !output_c
+        else
+          !output_c
+      in
       let retcode = command
           (Printf.sprintf "%s %s -o %s %s %s %s %s %s %s"
              Config.mkdll
              (if !debug then "-g" else "")
-             (prepostfix "dll" !output_c Config.ext_dll)
+             (prepostfix "dll" dllname Config.ext_dll)
              (String.concat " " !c_objs)
              (String.concat " " !c_opts)
              (String.concat " " !ld_opts)
@@ -308,7 +320,7 @@ let build_libs () =
   end;
   if !bytecode_objs <> [] then
     scommand
-      (sprintf "%s -a %s %s %s -o %s.cma %s %s -dllib -l%s -cclib -l%s \
+      (sprintf "%s -a %s %s %s -o %s.cma %s %s -dllib%s -l%s -cclib -l%s \
                    %s %s %s %s"
                   (transl_path !ocamlc)
                   (if !debug then "-g" else "")
@@ -317,6 +329,7 @@ let build_libs () =
                   !output
                   (String.concat " " !caml_opts)
                   (String.concat " " !bytecode_objs)
+                  (if !suffixed then "-suffixed" else "")
                   (Filename.basename !output_c)
                   (Filename.basename !output_c)
                   (String.concat " " (prefix_list "-ccopt " !c_opts))
diff --git a/tools/ocamlsize b/tools/ocamlsize
index 783068067f78..dfcc0adbf8fb 100755
--- a/tools/ocamlsize
+++ b/tools/ocamlsize
@@ -19,12 +19,25 @@ foreach $f (@ARGV) {
     open(FILE, $f) || die("Cannot open $f");
     read(FILE, $header, 2);
     if ($header eq '#!') {
-      $path = <FILE>;
-      if ($path = '/bin/sh') {
-        # exec form of the shebang header
-        $path = <FILE>;
+      chomp($path = <FILE>);
+      if ($path =~ m/\/sh$/) {
+        # shell-script form of the shebang header
+        chomp($path = <FILE>);
+        # exec form - used for -runtime-search absolute when the path to the
+        # runtime isn't valid as a #! line.
         if ($path =~ s/^exec '(.*)' "\$0" "\$@\"$/$1/ > 0) {
           $path =~ s/'\\''/'/g;
+        # Both -runtime-search fallback and -runtime-search enable define a
+        # variable r with the name of the runtime (see bytecomp/bytelink.ml)
+        } elsif ($path =~ s/^r='(.*)'$/$1/ > 0) {
+          $path =~ s/'\\''/'/g;
+          chomp($dir = <FILE>);
+          # In -runtime-search fallback, there will also be a path to the
+          # runtime defined the variable c.
+          if ($dir =~ s/^c='(.*)'"\$r"$/$1/ > 0) {
+            $dir =~ s/'\\''/'/g;
+            $path = "[$dir]$path";
+          }
         } else {
           undef $path;
         }
@@ -45,10 +58,19 @@ foreach $f (@ARGV) {
     }
     print $f, ":\n" if ($#ARGV > 0);
     if (not defined $path) {
-      $path =
-          $length{'RNTM'} > 0 ?
-              substr(&read_section('RNTM'), 0, -1) :
-              "(custom runtime)";
+      if ($length{'RNTM'} > 0) {
+        $path = &read_section('RNTM');
+        # RNTM is "\0ocamlrun" for -runtime-search enable
+        if ($path !~ s/^\0//) {
+          # RNTM is "/path/to/ocamlrun" for -runtime-search disable and
+          # "/path/to\0ocamlrun" for -runtime-search fallback. Transform the
+          # embedded "\0" into a directory separator and display the directory
+          # in square brackets (as above for the sh-case)
+          $path =~ s/^([^\/\\]*)([\\\/])([^\0]*)\0(.*)$/[$1$2$3$2]$4/
+        }
+      } else {
+        $path = '(custom runtime)';
+      }
     };
     printf ("\tcode: %-7d data: %-7d symbols: %-7d debug: %-7d\n",
             $length{'CODE'}, $length{'DATA'},
diff --git a/tools/opam/generate.ml b/tools/opam/generate.ml
new file mode 100644
index 000000000000..5c8d78e69f24
--- /dev/null
+++ b/tools/opam/generate.ml
@@ -0,0 +1,237 @@
+(**************************************************************************)
+(*                                                                        *)
+(*                                 OCaml                                  *)
+(*                                                                        *)
+(*            David Allsopp, University of Cambridge & Tarides            *)
+(*                                                                        *)
+(*   Copyright 2025 David Allsopp Ltd.                                    *)
+(*                                                                        *)
+(*   All rights reserved.  This file is distributed under the terms of    *)
+(*   the GNU Lesser General Public License version 2.1, with the          *)
+(*   special exception on linking described in the file LICENSE.          *)
+(*                                                                        *)
+(**************************************************************************)
+
+(* This script is called from the root of the repository at the end of
+   `make INSTALL_MODE=<opam|clone> install` and is responsible for converting
+   the various files generated by the installation backend into final output.
+   Parameters are the following Makefile variables:
+     $1 = $(INSTALL_MODE) (opam or clone)
+     $2 = $(OPAM_PACKAGE_NAME)
+     $3 = $(LN) *)
+
+let exit_because fmt = Printf.ksprintf (fun s -> prerr_endline s; exit 1) fmt
+
+let () =
+  if Array.length Sys.argv <> 4
+     || Sys.argv.(1) <> "clone" && Sys.argv.(1) <> "opam" then begin
+    exit_because "Invalid command line arguments"
+  end
+
+let mode = Sys.argv.(1)
+let package = Sys.argv.(2)
+let ln_command = Sys.argv.(3)
+
+let output_endline oc = Printf.kfprintf (fun oc -> output_char oc '\n') oc
+
+let write_install_lines oc file =
+  In_channel.with_open_text file @@
+    In_channel.fold_lines (fun _ -> output_endline oc "  %s") ()
+
+let remove_file = Sys.remove
+
+let output_section oc section =
+  let file = "opam-" ^ section in
+  if Sys.file_exists file then begin
+    let section =
+      if section = "lib" || section = "libexec" then
+        section ^ "_root"
+      else
+        section
+    in
+    output_endline oc {|%s: [
+%a]|} section write_install_lines file;
+    remove_file file
+  end
+
+(* See note in Makefile.common *)
+let valid_in_path = function '\'' | '"' | '\\' -> false | _ -> true
+let valid_in_section c = c <> '@' && valid_in_path c
+let valid_path path =
+  if String.for_all valid_in_path path then
+    path
+  else
+    exit_because "%S contains characters invalid in a path" path
+let valid_section dir =
+  if String.for_all valid_in_section dir then
+    dir
+  else
+    exit_because "%S contains characters invalid in a section" dir
+
+(* [generate_install file] processes then erases opam-bin, opam-lib opam-libexec
+   and opam-man to produce [file] *)
+let generate_install file =
+  Out_channel.with_open_text file @@ fun oc ->
+    List.iter (output_section oc) ["bin"; "lib"; "libexec"; "man"];
+    output_endline oc {|share_root: [
+  "config.cache" {"ocaml/config.cache"}
+  "config.status" {"ocaml/config.status"}
+]|}
+
+(* [process_clone oc process] processes clone-* in the current directory,
+   emitting mkdir commands to [oc] and passing the directory name and a channel
+   set to the start of each clone file to [process]. The clone files are erased
+   after processing. [prefix] is the literal string to place in double-quotes
+   for the installation prefix (either ["$1"] or ["$2"]). *)
+let process_clone oc ~prefix process =
+  let process_file file =
+    if String.starts_with ~prefix:"clone-" file then begin
+      let dir =
+        String.map (function '@' -> '/' | c -> c)
+                   (String.sub file 6 (String.length file - 6))
+        |> valid_section
+      in
+      output_endline oc {|mkdir -p "%s"'/%s'|} prefix dir;
+      In_channel.with_open_text file @@ process oc dir;
+      remove_file file
+    end
+  in
+  let files = Sys.readdir Filename.current_dir_name in
+  Array.sort String.compare files;
+  Array.iter process_file files
+
+(* [process_symlinks oc ~mkdir ~prefix] processes create-symlinks, if it exists,
+   writing any required mkdir commands to [oc] if [mkdir = true] and also the
+   appropriate ln / mklink commands. create-symlinks is erased after
+   processing. [prefix] is the literal string to place in double-quotes for the
+   installation prefix (either ["$1"] or ["$2"]). *)
+let process_symlinks oc ~mkdir ~prefix =
+  let module StringSet = Set.Make(String) in
+  let file = "create-symlinks" in
+  if Sys.file_exists file then
+    let lines =
+      let parse acc line =
+        match String.split_on_char ' ' line with
+        | [dir; target; source] ->
+            (valid_section dir, valid_path target, valid_path source)::acc
+        | _ ->
+            exit_because "Invalid line encountered in create-symlinks"
+      in
+      In_channel.with_open_text file @@ fun ic ->
+        List.rev (In_channel.fold_lines parse [] ic)
+    in
+    output_endline oc {|cd "%s"|} prefix;
+    let _ =
+      let create_dir seen (dir, _, _) =
+        if not (StringSet.mem dir seen) && String.contains dir '/' then
+          output_endline oc {|mkdir -p '%s'|} dir;
+        StringSet.add dir seen
+      in
+      List.fold_left create_dir StringSet.empty (if mkdir then lines else [])
+    in
+    if not Sys.win32 then
+      let ln (dir, target, source) =
+        output_endline oc {|%s '%s' '%s/%s'|} ln_command target dir source
+      in
+      List.iter ln lines
+    else begin
+      let mklink (dir, target, source) =
+        (* Convert all slashes to _two_ backslashes *)
+        let to_backslashes oc s =
+          output_string oc (String.concat {|\\|} (String.split_on_char '/' s))
+        in
+        output_endline oc
+          {|  cmd /c "mklink %a\\%s %s"|} to_backslashes dir source target
+      and cp (dir, target, source) =
+        output_endline oc {|  $CP '%s/%s' '%s/%s'|} dir target dir source
+      in
+      output_endline oc {|cmd /c "mklink __ln_test mklink-test"|};
+      output_endline oc {|if test -L "%s/__ln_test"; then|} prefix;
+      List.iter mklink lines;
+      output_endline oc {|else|};
+      List.iter cp lines;
+      output_endline oc {|fi|};
+      output_endline oc {|rm -f __ln_test|}
+    end;
+    remove_file file
+
+let copy_files oc dir =
+  In_channel.fold_lines (fun _ line ->
+    match String.split_on_char ' ' line with
+    | [source; dest] ->
+        let source = valid_path source in
+        let dest = valid_path dest in
+        output_endline oc {|cp '%s' "$1"'/%s/%s'|} source dir dest
+    | _ ->
+        exit_because "Invalid line encountered in clone files") ()
+
+let clone_files oc dir ic =
+  output_endline oc
+    {|src="$1" dest="$2"'/%s' xargs sh "$2/clone-files" <<'EOF'|} dir;
+  In_channel.fold_lines (fun _ -> output_endline oc "%s") () ic;
+  output_endline oc {|EOF|}
+
+let () =
+  if mode = "opam" then begin
+    generate_install (package ^ ".install");
+    (* The script must be written with Unix line-endings on Windows *)
+    Out_channel.with_open_bin (package ^ "-fixup.sh") @@ fun oc ->
+      output_endline oc {|#!/bin/sh
+set -eu|};
+      process_clone oc ~prefix:"$1" copy_files;
+      process_symlinks oc ~mkdir:true ~prefix:"$1"
+  end else begin
+    (* Don't pass -p to cp on Windows - it's never going to be relevant (no
+       execute bit which needs preserving) and there are scenarios in which it's
+       more likely to fail than add anything useful (especially if copying from
+       a Cygwin-managed build directory to /cygdrive) *)
+    let preserve = if Sys.win32 then "" else "p" in
+    (* The script must be written with Unix line-endings on Windows *)
+    Out_channel.with_open_bin (package ^ "-clone.sh") @@ fun oc ->
+      output_endline oc {|#!/bin/sh
+set -eu
+mkdir -p "$2"
+rm -f "$2/__cp_test" "$2/__ln_test"
+if cp --reflink=always "$1/doc/ocaml/LICENSE" "$2/__cp_test" 2>/dev/null; then
+  rm -f "$2/__cp_test"
+  CP='cp --reflink=always -%sf'
+  if ! test -e "$2/clone-files"; then
+    echo 'cd "$src" && '"$CP"' "$@" "$dest/"' > "$2/clone-files"
+  fi
+else
+  CP='cp -%sf'
+  if ! test -e "$2/clone-files"; then
+    if ln -f "$1/doc/ocaml/LICENSE" "$2/__ln_test" 2>/dev/null; then
+      rm -f "$2/__ln_test"
+      echo 'cd "$src" && ln -f "$@" "$dest/"' > "$2/clone-files"
+    else
+      echo 'cd "$src" && '"$CP"' "$@" "$dest/"' > "$2/clone-files"
+    fi
+  fi
+fi|} preserve preserve;
+      Out_channel.with_open_text "clone-share@ocaml" (fun oc ->
+        output_endline oc "share/ocaml/clone";
+        if Sys.file_exists "config.cache" then
+          output_endline oc "share/ocaml/config.cache");
+      process_clone oc ~prefix:"$2" clone_files;
+      (*  ld.conf is a configuration file, so is always copied.
+          Makefile.config and config.status will both contain the original
+          prefix, which must be updated. *)
+      output_endline oc {|cp "$1/lib/ocaml/ld.conf" "$2/lib/ocaml/ld.conf"
+cat > "$2/prefix.awk" <<'ENDAWK'
+{
+  rest = $0
+  while ((p = index(rest, ENVIRON["O"]))) {
+    printf "%%s%%s", substr(rest, 1, p-1), ENVIRON["N"]
+    rest = substr(rest, p + length(ENVIRON["O"]))
+  }
+  print rest
+}
+ENDAWK
+prefix="$(sed -ne 's/^prefix *= *//p' "$1/lib/ocaml/Makefile.config")"
+for file in lib/ocaml/Makefile.config share/ocaml/config.status; do
+  O="$prefix" N="$2" awk -f "$2/prefix.awk" "$1/$file" > "$2/$file"
+done
+rm -f "$2/clone-files" "$2/prefix.awk"|};
+      process_symlinks oc ~mkdir:false ~prefix:"$2"
+  end
diff --git a/toplevel/byte/topeval.ml b/toplevel/byte/topeval.ml
index 14c605039d56..b3823bd1a985 100644
--- a/toplevel/byte/topeval.ml
+++ b/toplevel/byte/topeval.ml
@@ -301,7 +301,7 @@ and really_load_file recursive ppf name filename ic =
                 "Cannot load required shared library %s.@.Reason: %s.@."
                 name reason;
               raise Load_failed)
-          lib.lib_dllibs;
+          (Dll.read_suffixed_dllibs_from_channel ic lib);
         List.iter (load_compunit ic filename ppf) lib.lib_units;
         true
       end else begin
diff --git a/utils/ccomp.ml b/utils/ccomp.ml
index defe4d2a4b92..d6818ef093a5 100644
--- a/utils/ccomp.ml
+++ b/utils/ccomp.ml
@@ -90,7 +90,13 @@ let compile_file ?output ?(opt="") ?stable_name name =
       ("", "") in
   let debug_prefix_map =
     match stable_name with
-    | Some stable when Config.c_has_debug_prefix_map ->
+    | Some stable
+      when Config.c_has_debug_prefix_map
+           && not (String.starts_with ~prefix:"mingw" Config.system) ->
+      (* -fdebug-prefix-map exists on mingw-w64 but at present it is not used
+         for BUILD_PATH_PREFIX_MAP because there isn't yet a good story for how
+         to deal with Cygwin, where the paths are Cygwin-style paths and MSYS2,
+         where they are native Windows paths. *)
       Printf.sprintf " -fdebug-prefix-map=%s=%s" name stable
     | Some _ | None -> "" in
   let exit =
diff --git a/utils/clflags.ml b/utils/clflags.ml
index be10f2352219..ab48a33138d1 100644
--- a/utils/clflags.ml
+++ b/utils/clflags.ml
@@ -38,9 +38,11 @@ module Float_arg_helper = Arg_helper.Make (struct
   end
 end)
 
-let objfiles = ref ([] : string list)   (* .cmo and .cma files *)
-and ccobjs = ref ([] : string list)     (* .o, .a, .so and -cclib -lxxx *)
-and dllibs = ref ([] : string list)     (* .so and -dllib -lxxx *)
+let objfiles = ref ([] : string list)         (* .cmo and .cma files *)
+and ccobjs = ref ([] : string list)           (* .o, .a, .so and -cclib -lxxx *)
+and dllibs = ref ([] : (bool * string) list)
+                                              (* .so, -dllib -lxxx and
+                                                 -dllib-suffixed -lxxx *)
 
 let cmi_file = ref None
 
@@ -48,6 +50,7 @@ let compile_only = ref false            (* -c *)
 and output_name = ref (None : string option) (* -o *)
 and include_dirs = ref ([] : string list) (* -I *)
 and hidden_include_dirs = ref ([] : string list) (* -H *)
+and standard_library_default = ref None (* -set-runtime-default *)
 and no_std_include = ref false          (* -nostdlib *)
 and no_cwd = ref false                  (* -nocwd *)
 and print_types = ref false             (* -i *)
@@ -85,6 +88,12 @@ and noinit = ref false                  (* -noinit *)
 and open_modules = ref []               (* -open *)
 and use_prims = ref ""                  (* -use-prims ... *)
 and use_runtime = ref ""                (* -use-runtime ... *)
+and target_bindir =                     (* -launch-method ... *)
+  ref Config.target_bindir
+and launch_method =
+  ref Config.launch_method
+and search_method =                     (* -search-method ... *)
+  ref Config.search_method
 and plugin = ref false                  (* -plugin ... *)
 and principal = ref false               (* -principal *)
 and real_paths = ref true               (* -short-paths *)
diff --git a/utils/clflags.mli b/utils/clflags.mli
index 248a7d86e620..48fad440b062 100644
--- a/utils/clflags.mli
+++ b/utils/clflags.mli
@@ -70,12 +70,13 @@ val use_inlining_arguments_set : ?round:int -> inlining_arguments -> unit
 
 val objfiles : string list ref
 val ccobjs : string list ref
-val dllibs : string list ref
+val dllibs : (bool * string) list ref
 val cmi_file : string option ref
 val compile_only : bool ref
 val output_name : string option ref
 val include_dirs : string list ref
 val hidden_include_dirs : string list ref
+val standard_library_default : string option ref
 val no_std_include : bool ref
 val no_cwd : bool ref
 val print_types : bool ref
@@ -113,6 +114,9 @@ val noinit : bool ref
 val noversion : bool ref
 val use_prims : string ref
 val use_runtime : string ref
+val target_bindir : string ref
+val launch_method : Config.launch_method ref
+val search_method : Config.search_method ref
 val plugin : bool ref
 val principal : bool ref
 val real_paths : bool ref
diff --git a/utils/config.common.ml.in b/utils/config.common.ml.in
index 3603fe6c60c7..c5459b93efc0 100644
--- a/utils/config.common.ml.in
+++ b/utils/config.common.ml.in
@@ -20,6 +20,28 @@
 (* The main OCaml version string has moved to ../build-aux/ocaml_version.m4 *)
 let version = Sys.ocaml_version
 
+(* is_official_release and release_number are automatically updated autoconf
+   from values in ../build-aux/ocaml_version.m4 - do not edit these lines
+   directly. *)
+let is_official_release = false
+let release_number = 19
+
+external standard_library_default : unit -> string = "%standard_library_default"
+
+let standard_library_default_raw = standard_library_default ()
+
+external stdlib_dirs : string -> string * string option
+   = "caml_sys_get_stdlib_dirs"
+
+let standard_library_default, relative_root_dir =
+  stdlib_dirs standard_library_default_raw
+
+let standard_library_relative =
+  if relative_root_dir = None then
+    None
+  else
+    Some standard_library_default_raw
+
 let standard_library =
   try
     Sys.getenv "OCAMLLIB"
@@ -29,6 +51,13 @@ let standard_library =
   with Not_found ->
     standard_library_default
 
+let bindir = Option.value ~default:bindir relative_root_dir
+let target_bindir =
+  if target_bindir = Filename.current_dir_name then
+    Filename.dirname Sys.executable_name
+  else
+    target_bindir
+
 let exec_magic_number = {magic|@EXEC_MAGIC_NUMBER@|magic}
     (* exec_magic_number is duplicated in runtime/caml/exec.h *)
 and cmi_magic_number = {magic|@CMI_MAGIC_NUMBER@|magic}
@@ -46,6 +75,21 @@ let safe_string = true
 let default_safe_string = true
 let naked_pointers = false
 
+type launch_method = Executable | Shebang of string option
+type search_method = Disable | Fallback | Enable
+
+let launch_method =
+  match launch_method with
+  | "exe" -> Executable
+  | "sh" -> Shebang None
+  | _ -> Shebang (Some launch_method)
+
+let search_method =
+  match search_method with
+  | "enable" -> Enable
+  | "fallback" -> Fallback
+  | _ -> Disable
+
 let interface_suffix = ref ".mli"
 
 let max_tag = 243
@@ -71,9 +115,13 @@ let configuration_variables () =
   let p x v = (x, String v) in
   let p_int x v = (x, Int v) in
   let p_bool x v = (x, Bool v) in
+  let standard_library_relative =
+    Option.value ~default:"" standard_library_relative
+  in
 [
   p "version" version;
   p "standard_library_default" standard_library_default;
+  p "standard_library_relative" standard_library_relative;
   p "standard_library" standard_library;
   p "ccomp_type" ccomp_type;
   p "c_compiler" c_compiler;
@@ -110,6 +158,8 @@ let configuration_variables () =
   p_bool "systhread_supported" systhread_supported;
   p "host" host;
   p "target" target;
+  p "bytecode_runtime_id" bytecode_runtime_id;
+  p "native_runtime_id" native_runtime_id;
   p_bool "flambda" flambda;
   p_bool "safe_string" safe_string;
   p_bool "default_safe_string" default_safe_string;
diff --git a/utils/config.fixed.ml b/utils/config.fixed.ml
index 807b92935531..02894bc6b3b0 100644
--- a/utils/config.fixed.ml
+++ b/utils/config.fixed.ml
@@ -21,7 +21,7 @@
 let boot_cannot_call s = "/ The boot compiler should not call " ^ s
 
 let bindir = "/tmp"
-let standard_library_default = "/tmp"
+let target_bindir = bindir
 let ccomp_type = "n/a"
 let c_compiler = boot_cannot_call "the C compiler"
 let c_output_obj = ""
@@ -35,6 +35,7 @@ let bytecomp_c_libraries = ""
 let bytecomp_c_compiler = ""
 let native_c_compiler = c_compiler
 let native_c_libraries = ""
+let compression_c_libraries = ""
 let native_ldflags = ""
 let native_pack_linker = boot_cannot_call "the linker"
 let default_rpath = ""
@@ -52,6 +53,8 @@ let windows_unicode = false
 let flat_float_array = true
 let function_sections = false
 let afl_instrument = false
+let bytecode_runtime_id = ""
+let native_runtime_id = ""
 let native_compiler = false
 let tsan = false
 let architecture = "none"
@@ -71,3 +74,6 @@ let target = host
 let systhread_supported = false
 let flexdll_dirs = []
 let ar_supports_response_files = true
+let suffixing = false
+let launch_method = "sh"
+let search_method = "always"
diff --git a/utils/config.generated.ml.in b/utils/config.generated.ml.in
index aa0345540968..71093a1e5dbb 100644
--- a/utils/config.generated.ml.in
+++ b/utils/config.generated.ml.in
@@ -19,8 +19,7 @@
    than compiled on its own *)
 
 let bindir = {@QS@|@ocaml_bindir@|@QS@}
-
-let standard_library_default = {@QS@|@ocaml_libdir@|@QS@}
+let target_bindir = {@QS@|@TARGET_BINDIR@|@QS@}
 
 let ccomp_type = {@QS@|@ccomptype@|@QS@}
 let c_compiler = {@QS@|@CC@|@QS@}
@@ -44,6 +43,7 @@ let bytecomp_c_compiler =
 let native_c_compiler =
   c_compiler ^ " " ^ native_cflags ^ " " ^ native_cppflags
 let native_c_libraries = {@QS@|@cclibs@|@QS@}
+let compression_c_libraries = {@QS@|@zstd_libs@|@QS@}
 let native_ldflags = {@QS@|@native_ldflags@|@QS@}
 let native_pack_linker = {@QS@|@PACKLD@|@QS@}
 let default_rpath = {@QS@|@rpath@|@QS@}
@@ -65,6 +65,9 @@ let flat_float_array = @flat_float_array@
 let function_sections = @function_sections@
 let afl_instrument = @afl@
 
+let bytecode_runtime_id = {@QS@|@bytecode_runtime_id@|@QS@}
+let native_runtime_id = {@QS@|@native_runtime_id@|@QS@}
+
 let native_compiler = @native_compiler@
 
 let architecture = {@QS@|@arch@|@QS@}
@@ -92,3 +95,9 @@ let flexdll_dirs = [@flexdll_dir@]
 let ar_supports_response_files = @ar_supports_response_files@
 
 let tsan = @tsan@
+
+let suffixing = @suffixing@
+
+let launch_method = {@QS@|@launch_method_target@|@QS@}
+
+let search_method = {@QS@|@runtime_search_target@|@QS@}
diff --git a/utils/config.mli b/utils/config.mli
index 51e31a37294c..7ccbd70f80d4 100644
--- a/utils/config.mli
+++ b/utils/config.mli
@@ -23,11 +23,43 @@
 val version: string
 (** The current version number of the system *)
 
+val release_number: int
+(** The release number for the compiler
+
+    @since 5.4.2 *)
+
+val is_official_release: bool
+(** True if the compiler is an unmodified official OCaml release
+
+    @since 5.4.2 *)
+
 val bindir: string
-(** The directory containing the binary programs *)
+(** The directory containing the binary programs. If the compiler was configured
+    with [--with-relative-libdir] then this will be the directory containing the
+    currently executing runtime. *)
+
+val standard_library_relative: string option
+(** The explicit relative path from the compiler binaries to the standard
+    libraries directory if the compiler was configured with
+    [--with-relative-libdir], or [None] otherwise.
+
+    @since 5.3.2 *)
+
+val target_bindir: string
+(** The directory containing the runtime binaries on the target system
+
+    @since 5.4.2 *)
+
+val standard_library_default: string
+(** The effective value for the default directory containing the standard
+    libraries. This is always an absolute path, computed using
+    {!standard_library_relative} if necessary.
+
+    @since 5.3.2 *)
 
 val standard_library: string
-(** The directory containing the standard libraries *)
+(** The effective directory containing the standard libraries, taking CAMLLIB
+    and OCAMLLIB into account. *)
 
 val ccomp_type: string
 (** The "kind" of the C compiler, assembler and linker used: one of
@@ -65,6 +97,12 @@ val bytecomp_c_libraries: string
 val native_c_libraries: string
 (** The C libraries to link with native-code programs *)
 
+val compression_c_libraries: string
+(** The C libraries needed with -lcomprmarsh (should appear before
+    {!native_c_libraries} in a call to the C compiler)
+
+    @since 5.3.2 *)
+
 val native_ldflags : string
 (* Flags to pass to the system linker *)
 
@@ -253,6 +291,57 @@ val ar_supports_response_files: bool
 val tsan : bool
 (** Whether ThreadSanitizer instrumentation is enabled *)
 
+(** Launch mechanisms for bytecode executables
+
+    @since 5.4.2 *)
+type launch_method =
+| Executable
+    (** Use the executable launcher stub *)
+| Shebang of string option
+    (** Use a shebang-style launcher. Whenever possible, the interpreter will be
+        the runtime itself, but if the path to the runtime is not valid for a
+        shebang line, then a shell script is generated. When this is necessary,
+        the parameter in [Shebang (Some sh)] is the full path to [sh]; if the
+        parameter is [None], then the linker searches PATH for [sh]. *)
+
+val launch_method : launch_method
+(** Default launch mechanism for bytecode executables
+
+    @since 5.4.2 *)
+
+(** Mechanisms used by tendered bytecode executables to locate the interpreter
+
+    @since 5.4.2 *)
+type search_method =
+| Disable
+    (** Interpreter searching disabled - check fixed absolute location only *)
+| Fallback
+    (** Check fixed absolute location first, but fall back to a search if that
+        fails *)
+| Enable
+    (** Always search for the interpreter *)
+
+val search_method : search_method
+(** Default search mechanism for bytecode executables
+
+    @since 5.4.2 *)
+
+val suffixing : bool
+(** Whether the runtime executable and shared library filenames and C stub
+    library filenames are being mangled with Runtime IDs and the {!target}.
+
+    @since 5.4.2 *)
+
+val bytecode_runtime_id : string
+(** The Runtime ID for this build of the bytecode runtime system
+
+    @since 5.4.2 *)
+
+val native_runtime_id : string
+(** The Runtime ID for this build of the native runtime system
+
+    @since 5.4.2 *)
+
 (** Access to configuration values *)
 val print_config : out_channel -> unit
 
diff --git a/utils/misc.ml b/utils/misc.ml
index b3d75dbb8664..5d9afaa80bed 100644
--- a/utils/misc.ml
+++ b/utils/misc.ml
@@ -1390,3 +1390,130 @@ module Magic_number = struct
            | Error err -> Error (Unexpected_error err)
            | Ok () -> Ok info
 end
+
+module RuntimeID = struct
+  type t = {
+    dev: bool;
+    release: int;
+    reserved: int;
+    no_flat_float_array: bool;
+    fp: bool;
+    tsan: bool;
+    int31: bool;
+    static: bool;
+    no_compression: bool;
+    ansi: bool;
+  }
+
+  let make fn ?(dev = not Config.is_official_release)
+              ?(release = Config.release_number)
+              ?(reserved = Config.reserved_header_bits)
+              ?(no_flat_float_array = not Config.flat_float_array)
+              ?(fp = Config.with_frame_pointers)
+              ?(tsan = Config.tsan)
+              ?(int31 = (Sys.int_size = 31))
+              ?(static = not Config.supports_shared_libraries)
+              ?(no_compression = (Config.compression_c_libraries = ""))
+              ?(ansi = Sys.win32 && not Config.windows_unicode) () =
+    if release < 0 || release > 63 || reserved < 0 || reserved > 31 then
+      invalid_arg fn
+    else
+      {dev; release; reserved; no_flat_float_array; fp; tsan; int31; static;
+       no_compression; ansi}
+
+  let make_zinc =
+    make "Misc.RuntimeID.make_zinc"
+      ~reserved:0 ~fp:false ~tsan:false ~ansi:false
+
+  let make_bytecode =
+    make "Misc.RuntimeID.make_bytecode" ~fp:false ~tsan:false
+
+  let make_native = make "Misc.RuntimeID.make_native"
+
+  let is_zinc = function
+  | {dev = _; release = _; reserved = 0; no_flat_float_array = _; fp = false;
+     tsan = false; int31 = _; static = _; no_compression = _; ansi = false} ->
+      true
+  | _ ->
+      false
+
+  let is_bytecode = function
+  | {dev = _; release = _; reserved = _; no_flat_float_array = _; fp = false;
+     tsan = false; int31 = _; static = _; no_compression = _; ansi = _} -> true
+  | _ -> false
+
+  let is_native _ = true
+
+  let to_string t =
+    let alpha = "0123456789abcdefghijklmnopqrstuv" in
+    let bit bit cond = if cond then 1 lsl bit else 0 in
+    let q0 =
+      (bit 0 t.dev) lor
+      ((t.release lsl 1) land 0b11110) (* 4 bits *)
+    in
+    let q1 =
+      t.release lsr 4 lor               (* 2 bits *)
+      ((t.reserved lsl 2) land 0b11100) (* 3 bits *)
+    in
+    let q2 =
+      t.reserved lsr 3 lor (* 2 bits *)
+      bit 2 t.no_flat_float_array lor
+      bit 3 t.fp lor
+      bit 4 t.tsan
+    in
+    let q3 =
+      bit 0 t.int31 lor
+      bit 1 t.static lor
+      bit 2 t.no_compression lor
+      bit 3 t.ansi
+      (* bit 4 is unused *)
+    in
+    Printf.sprintf "%c%c%c%c" alpha.[q0] alpha.[q1] alpha.[q2] alpha.[q3]
+
+  let of_string s =
+    if String.length s <> 4 then
+      None
+    else
+      let convert c =
+        match c with
+        | '0'..'9' -> Char.code c - Char.code '0'
+        | 'a'..'v' -> Char.code c - Char.code 'a' + 10
+        | _ -> min_int
+      in
+      let set bit q = (q land (1 lsl bit) <> 0) in
+      let q0 = convert s.[0] in
+      let q1 = convert s.[1] in
+      let q2 = convert s.[2] in
+      let q3 = convert s.[3] in
+      if q0 + q1 + q2 + q3 >= 0 then
+        Some {dev = set 0 q0; release = ((q1 land 0b11) lsl 4) lor (q0 lsr 1);
+              reserved = ((q2 land 0b11) lsl 2) lor (q1 lsr 2);
+              no_flat_float_array = set 2 q2; fp = set 3 q2; tsan = set 4 q2;
+              int31 = set 0 q3; static = set 1 q3; no_compression = set 2 q3;
+              ansi = set 3 q3; (* bit 4 of q3 is unused *)}
+      else
+        None
+
+  let ocamlrun variant runtime_id =
+    if is_zinc runtime_id then
+      Printf.sprintf "ocamlrun%s-%s" variant (to_string runtime_id)
+    else
+      invalid_arg "Misc.RuntimeID.ocamlrun"
+
+  let shared_runtime ?runtime_id ?(host = Config.target) ?(prefix = "-l")
+                     backend_type =
+    match backend_type with
+    | Sys.Native ->
+        let runtime_id = Option.value ~default:(make_native ()) runtime_id in
+        Printf.sprintf "%sasmrun-%s-%s" prefix host (to_string runtime_id)
+    | Sys.Bytecode ->
+        let runtime_id = Option.value ~default:(make_bytecode ()) runtime_id in
+        Printf.sprintf "%scamlrun-%s-%s" prefix host (to_string runtime_id)
+    | Sys.Other _ ->
+        invalid_arg "Misc.RuntimeID.shared_runtime"
+
+  let stubslib ?(runtime_id = make_bytecode ())
+               ?(host = Config.target)
+               name =
+    Printf.sprintf "%s-%s-%s" name host (to_string runtime_id)
+end
diff --git a/utils/misc.mli b/utils/misc.mli
index 54354eba56ab..8bf42334eed9 100644
--- a/utils/misc.mli
+++ b/utils/misc.mli
@@ -823,6 +823,106 @@ module Utf8_lexeme: sig
       are not checked. *)
 end
 
+module RuntimeID : sig
+  (** Manipulation of the Runtime ID values used to mangle the filenames of
+      shared libraries and the bytecode interpreters.
+
+      @since 5.3.2 *)
+
+  (** Runtime IDs *)
+  type t = private {
+    dev: bool;
+      (** [true] if this not an unaltered official release of OCaml *)
+    release: int;
+      (** Release number (OCaml 5.5 is release 21) *)
+    reserved: int;
+      (** The number of reserved bits (0-31) in the {v value v} header *)
+    no_flat_float_array: bool;
+      (** [true] if float arrays must be boxed (i.e. configured with
+          {v --disable-flat-float-array v}) *)
+    fp: bool;
+      (** [true] if frame pointers are required (i.e. configured with
+          {v --enable-frame-pointers v} *)
+    tsan: bool;
+      (** [true] if ThreadSanitizer (TSAN) is required (i.e. configured with
+          {v --enable-tsan v}) *)
+    int31: bool;
+      (** [true] if the platform has 31-bit [int]s (i.e. 32-bit systems) *)
+    static: bool;
+      (** [true] if dynamic loading of libraries is not supported *)
+    no_compression: bool;
+      (** [true] if compressed marshalling is not supported *)
+    ansi: bool;
+      (** [true] if Unicode support on Windows is disabled *)
+  }
+
+  val make_zinc: ?dev:bool -> ?release:int
+    -> ?no_flat_float_array:bool
+    -> ?int31:bool -> ?static:bool -> ?no_compression:bool
+    -> unit -> t
+  (** Returns the Zinc Runtime ID for the given parameters (using default values
+      from {!Config} and {!Sys} as necessary) *)
+
+  val make_bytecode: ?dev:bool -> ?release:int
+    -> ?reserved:int -> ?no_flat_float_array:bool
+    -> ?int31:bool -> ?static:bool -> ?no_compression:bool
+    -> ?ansi:bool
+    -> unit -> t
+  (** Returns the Bytecode Runtime ID for the given parameters (using default
+      values from {!Config} and {!Sys} as necessary) *)
+
+  val make_native: ?dev:bool -> ?release:int
+    -> ?reserved:int -> ?no_flat_float_array:bool -> ?fp:bool -> ?tsan:bool
+    -> ?int31:bool -> ?static:bool -> ?no_compression:bool
+    -> ?ansi:bool
+    -> unit -> t
+  (** Returns the Native Runtime ID for the given parameters (using default
+      values from {!Config} and {!Sys} as necessary) *)
+
+  val is_zinc: t -> bool
+  (** [is_zinc t] is true if [t] can be used as a Zinc Runtime ID *)
+
+  val is_bytecode: t -> bool
+  (** [is_bytecode t] is true if [t] can be used as a Bytecode Runtime ID *)
+
+  val is_native: t -> bool
+  (** [is_native t] is true if [t] can be used as a Native Runtime ID *)
+
+  val to_string: t -> string
+  (** Returns the 4-character representation of a {!t} *)
+
+  val of_string: string -> t option
+  (** Converts the 4-character representation back to a {!t} *)
+
+  val ocamlrun: string -> t -> string
+  (** [ocamlrun variant runtime_id] returns the name for the runtime for the
+      given Zinc Runtime ID. *)
+
+  val shared_runtime: ?runtime_id:t -> ?host:string
+    -> ?prefix:string -> Sys.backend_type -> string
+  (** [shared_runtime ?runtime_id ?host ?prefix backend] returns the name of the
+      shared runtime for the given [backend]. [runtime_id] defaults to
+      {!make_bytecode} if [backend = Sys.Bytecode] and {!make_native} if
+      [backend = Sys.Native] and [host] to {!Config.target}. [prefix] defaults
+      to ["-l"] and the function does not append {!Config.ext_dll}.
+
+      e.g. [shared_runtime ~host:"x86_64-pc-linux-gnu" Native
+              = "-lasmrun-x86_64-pc-linux-gnu-b100"] for a default OCaml 5.5
+           build on a 64-bit system with shared library support and compressed
+           marshalling. *)
+
+  val stubslib: ?runtime_id:t -> ?host:string -> string -> string
+  (** [stublibs ?runtime_id ?host dllname] returns the name for the given DLL
+      basename. [dllname] should not include {!Config.ext_dll} (and the result
+      does not include it either). [host] and [runtime_id] default to
+      {!Config.target} and {!make_bytecode} respectively.
+
+      e.g. [stubslib ~host:"x86_64-pc-linux-gnu" "dllunixbyt"
+              = "dllunixbyt-x86_64-pc-linux-gnu-001b"] for a default OCaml 5.5
+           build on a 64-bit system with shared library support and compressed
+           marshalling. *)
+end
+
 (** {1 Miscellaneous type aliases} *)
 
 type filepath = string