Linking Android Chrome for arm64 gives: Unsupported relocation type Unknown aarch64 relocation type 0x13a

[agrieve]

Repro steps:

1. Checkout chrome: https://chromium.googlesource.com/chromium/src/+/main/docs/android_build_instructions.md#Get-the-code
2. Write out/Debug/args.gn:

target_os = "android"
treat_warnings_as_errors = false
experimental_linker_path = "PATH_TO/wild"
arm_control_flow_integrity = "none"
is_component_build=false

3. autoninja -C out/Debug libchrome.so

This gives:

stdout:
WARNING: wild: --fix-cortex-a53-843419 is not yet supported
WARNING: wild: --use-android-relr-tags is not yet supported
WARNING: wild: --pack-dyn-relocs=relr is not yet supported
stderr:

thread '<unnamed>' (2081826) panicked at libwild/src/elf_aarch64.rs:135:79:
called `Result::unwrap()` on an `Err` value: Unsupported relocation type Unknown aarch64 relocation type 0x13a
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
...

You can also repro on a vastly smaller target:

autoninja -C out/Debug libchrome_crashpad_handler.so

It seems mold has the same issue, and provides the source paths of the unrecognized relocations. Filed rui314/mold#1561

• If it's easier to use a llvm --reproduce tarball, I've attached that here: https://crbug.com/40208899#comment26 (for libchrome_crashpad_handler.so)

[marxin]

The missing relocation is this one:

wild/linker-utils/src/aarch64.rs

Lines 177 to 178 in 8f3f4df

	// TODO: missing in upstream header file (as well as in Object crate):
	// object::elf::R_AARCH64_PLT32

and I can prepare a fix later today.

[mati865]

Judging by Mold errors you will also need to implement

wild/linker-utils/src/aarch64.rs

Line 474 in 8f3f4df

// object::elf::R_AARCH64_GOTPCREL32

I guess Wild just reported the first missing one.

[marxin]

I guess Wild just reported the first missing one.

Good point, I've just opened a PR adding the constants: gimli-rs/object#865.

[marxin]

@agrieve can you test if the provided PR resolves your issue?

[agrieve]

It didn't seem to, but I'm new to rust, and just used gemini to guide me through this, so lmk if I've done something wrong...

Patch to wild:

diff --git a/Cargo.lock b/Cargo.lock
index 582a42d..ecb10e6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1238,7 +1238,6 @@ dependencies = [
 [[package]]
 name = "object"
 version = "0.38.1"
-source = "git+https://github.com/gimli-rs/object?rev=ae958b9f2c8a3a56fe19bb4b380144a32eebb770#ae958b9f2c8a3a56fe19bb4b380144a32eebb770"
 dependencies = [
  "memchr",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 7370e49..16ec69f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -239,3 +239,6 @@ needless_pass_by_ref_mut = "warn"
 # We do a bit of hashing, especially in the integration tests. Optimising this speeds up tests.
 [profile.dev.package."foldhash"]
 opt-level = 2
+
+[patch."https://github.com/gimli-rs/object"]
+object = { path = "external/object" }
diff --git a/linker-utils/src/aarch64.rs b/linker-utils/src/aarch64.rs
index 658976c..cfbc202 100644
--- a/linker-utils/src/aarch64.rs
+++ b/linker-utils/src/aarch64.rs
@@ -168,9 +168,13 @@ pub const fn relocation_type_from_raw(r_type: u32) -> Option<RelocationKindInfo>
             AllowedRange::new(-(2i64.pow(15)), 2i64.pow(16)),
             1,
         ),
-
-        // TODO: missing in upstream header file (as well as in Object crate):
-        // object::elf::R_AARCH64_PLT32
+        object::elf::R_AARCH64_PLT32 => (
+            RelocationKind::PltRelative,
+            RelocationSize::ByteSize(4),
+            None,
+            AllowedRange::new(-(2i64.pow(31)), 2i64.pow(32)),
+            1,
+        ),

         // 5.7.6   Static AArch64 relocations
         // Group relocations to create a 16-, 32-, 48-, or 64-bit unsigned data value or address
@@ -465,8 +469,13 @@ pub const fn relocation_type_from_raw(r_type: u32) -> Option<RelocationKindInfo>
             AllowedRange::new(-(2i64.pow(31)), 2i64.pow(31)),
             1,
         ),
-        // TODO: missing in upstream header file (as well as in Object crate)
-        // object::elf::R_AARCH64_GOTPCREL32
+        object::elf::R_AARCH64_GOTPCREL32 => (
+            RelocationKind::GotRelative,
+            RelocationSize::ByteSize(4),
+            None,
+            AllowedRange::new(-(2i64.pow(31)), 2i64.pow(31)),
+            1,
+        ),
         object::elf::R_AARCH64_GOT_LD_PREL19 => (
             RelocationKind::GotRelative,
             RelocationSize::bit_mask_aarch64(2, 21, AArch64Instruction::LdSt),

And then in external/object, I applied the gimli patch.

I then built with:

RUSTFLAGS="-C target-feature=+crt-static" cargo +nightly build --release --target "x86_64-unknown-linux-gnu" --bin wild

The resulting binary yielded:

WARNING: wild: --fix-cortex-a53-843419 is not yet supported
WARNING: wild: --use-android-relr-tags is not yet supported
WARNING: wild: --pack-dyn-relocs=relr is not yet supported
stderr:
wild: error: Failed copying from obj/third_party/angle/libANGLE_no_vulkan/validationES.o (3840 (15/0)) to output file
  Caused by:
    Failed to apply relocations in section `.text` of obj/third_party/angle/libANGLE_no_vulkan/validationES.o
    Failed to apply relocation of type R_AARCH64_CALL26 to symbol `std::__Cr::basic_ostream<char, std::__Cr::char_traits<char> >::operator<<(int)` (358500 local=657) in file #3840 (15/0) (obj/third_party/angle/libANGLE_no_vulkan/validationES.o) defined as 12162586 in file #121117 (473/29) (obj/buildtools/third_party/libc++/libc++/ios.instantiations.o) (ABSOLUTE) at offset 0x84c
    Relocation 236201992 outside of bounds [-134217728, 134217728)

With only the change to gimli, I get the original failure message.

[marxin]

Well, you can just checkout this PR and build wild from it. Anyways, it's leading to a different error:

    Failed to apply relocation of type R_AARCH64_CALL26 to symbol `std::__Cr::basic_ostream<char, std::__Cr::char_traits<char> >::operator<<(int)` (358500 local=657) in file #3840 (15/0) (obj/third_party/angle/libANGLE_no_vulkan/validationES.o) defined as 12162586 in file #121117 (473/29) (obj/buildtools/third_party/libc++/libc++/ios.instantiations.o) (ABSOLUTE) at offset 0x84c
    Relocation 236201992 outside of bounds [-134217728, 134217728)

which is a situation where we cannot apply the relocation as it's out of range. Based on the spec, our validation is correct:

R_<CLS>_CALL26	S+A-P	Set a CALL immediate field to bits [27:2] of X; check that -227 <= X < 227

am curious if other linkers can build the Chromium on the given platform?

[mati865]

Looks very much like llvm/llvm-project#52767 (albeit the platform is different) and they are using range extension thunks to solve the problem.
Since this is a 225 MiB jump, Wild would also need to implement that.