lto?: Wild runs out of file descriptors when building WebKit (`wild: error: Failed to open input file "..." Caused by: No file descriptors available (os error 24)`)

[zyxhere]

When compiling WebKitGTK with LTO and using wild as the linker, the final linking failed:

[8434/8453] : && /usr/lib/ccache/bin/x86_64-pc-linux-musl-clang++ \
-fPIC -fdiagnostics-color=always -fcolor-diagnostics -Wextra -Wall -Werror=undefined-internal -Werror=undefined-inline -pipe \
-Wno-noexcept-type -Wno-psabi -Wno-misleading-indentation -Wno-parentheses-equality -Qunused-arguments -Wundef -Wpointer-arith -Wmissing-format-attribute \
-Wformat-security -Wcast-align -Wno-tautological-compare -fasynchronous-unwind-tables -fdebug-types-section \
-march=native -O2 -pipe -flto=thin -fno-semantic-interposition -ftrivial-auto-var-init=zero -Werror=format-security -g1 \
-fno-strict-aliasing -fno-exceptions -fno-rtti -fcoroutines -ffunction-sections -fdata-sections  -shared -Wl,--no-undefined \
-Wl,-O1,--as-needed,--sort-common,--gc-sections,-Bsymbolic-functions,--build-id=sha1,-z,pack-relative-relocs,-z,relro,-z,now -flto -fuse-ld=wild \
-Wl,--gc-sections -Wl,--disable-new-dtags  -Wl,--version-script,/var/tmp/portage/net-libs/webkit-gtk-2.50.5-r600/work/webkitgtk-2.50.5/Source/WebKit/webkitglib-symbols.map \
-Wl,-soname,libwebkitgtk-6.0.so.4 -o lib/libwebkitgtk-6.0.so.4.13.8 @CMakeFiles/WebKit.rsp && :
ninja: job failed: : && /usr/lib/ccache/bin/x86_64-pc-linux-musl-clang++ \
-fPIC -fdiagnostics-color=always -fcolor-diagnostics -Wextra -Wall -Werror=undefined-internal -Werror=undefined-inline -pipe \
-Wno-noexcept-type -Wno-psabi -Wno-misleading-indentation -Wno-parentheses-equality -Qunused-arguments -Wundef -Wpointer-arith -Wmissing-format-attribute -Wformat-security -Wcast-align -Wno-tautological-compare -fasynchronous-unwind-tables -fdebug-types-section \
-march=native -O2 -pipe -flto=thin -fno-semantic-interposition -ftrivial-auto-var-init=zero -Werror=format-security -g1 \
-fno-strict-aliasing -fno-exceptions -fno-rtti -fcoroutines -ffunction-sections -fdata-sections  -shared -Wl,--no-undefined \
-Wl,-O1,--as-needed,--sort-common,--gc-sections,-Bsymbolic-functions,--build-id=sha1,-z,pack-relative-relocs,-z,relro,-z,now -flto -fuse-ld=wild \
-Wl,--gc-sections -Wl,--disable-new-dtags  -Wl,--version-script,/var/tmp/portage/net-libs/webkit-gtk-2.50.5-r600/work/webkitgtk-2.50.5/Source/WebKit/webkitglib-symbols.map \
-Wl,-soname,libwebkitgtk-6.0.so.4 -o lib/libwebkitgtk-6.0.so.4.13.8 @CMakeFiles/WebKit.rsp && :
WARNING: wild: -z pack-relative-relocs is not yet supported
wild: error: Failed to open input file `Source/WebCore/CMakeFiles/WebCore.dir/./page/scrolling/coordinated/ScrollingTreeFixedNodeCoordinated.cpp.o`
  Caused by:
    No file descriptors available (os error 24)

x86_64-pc-linux-musl-clang++: error: linker command failed with exit code 255 (use -v to see invocation)
ninja: subcommand failed

I thinks its a similar situation to the one with mold where it also ran out of file descriptors when using LTO with clang rui314/mold#1362
I'll check later (probably this weekend) if this happens without LTO and/or with GCC but WebKit takes forever to compile (and loads of RAM) so will take a while to test for that.

[mati865]

It does not happen without LTO, I've built webkitgtk like a dozen times with fairly recent Wild version (~2-3 weeks old).

[zyxhere]

On Thu, 2026-02-19 at 11:37 -0800, Mateusz Mikuła wrote: mati865 left a comment (wild-linker/wild#1572) It does not happen without LTO, I've built webkit like a dozen times with fairly recent Wild version (~2-3 weeks old).

So its rui314/mold#1362 but for wild then

[mati865]

Not necessarily, unless I missed something I don't see the leak.

However, Wild keeps FD after mmaping the file, but it's unnecessary: https://stackoverflow.com/a/17490185/5940067
I don't know how hard it would be to stop doing that.

[davidlattimore]

Wild normally closes files after it has mmapped them. However, if the file is an LTO input, then it keeps it open since the plugin API needs to be provided the file descriptor. There is a somewhat more recent addition to the plugin API (GetView) that allows the plugin to get access to the mmapped file, but that API is only used by the LLVM plugin, not GCC. Also, even when the API is used, you still pass the file descriptor to the plugin initially.

My guess as to a fix is to increase the file descriptor limit, which I believe can be done with setrlimit.

[zyxhere]

Only happens when using LTO indeed. Another thing I noticed in this new build is this message:

Linker plugin message: LLVM gold plugin: %s
Linker plugin warning: LLVM gold plugin: %s

They're lots of it in this new build but not the original. Attaching the build logs

log.gz

Also heres the first build where wild also ran out of file descriptors but didn't output those LLVM gold plugin: %s messages

build.log.gz

[davidlattimore]

Unfortunately the linker plugin API relies on varargs for printing messages. Rust's support for implementing C varargs functions isn't stable (feature c_variadic). We want to be able to compile wild on stable rust. I guess we could detect if we're building on nightly and use the feature there to get the full message. Either that or we could compile a small bit of C code that converts to a full string and passes that through to the rust code.

[mati865]

Technically, it's doable with inline assembly, but that sounds even worse than having to deal with C compiler.