Cross linker lto error: conflict llvm version.

[Wyvern]

rustc 1.91.0-nightly (f2824da98 2025-08-28)
build with -Zbuild-std got compile error like below:

error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "-Wl,-exported_symbols_list" "-Wl,/var/folders/x7/ch5v91h56_zbvbd1y2f600dm0000gn/T/rustcfEM3e0/list" "<1 object files omitted>" "/.../build-dir/aarch64-apple-ios/src/deps/libcompiler_builtins-75a2186d30a4b1be.rlib" "-liconv" "-lSystem" "-lc" "-lm" "-target" "arm64-apple-ios10.0.0" "-o" "/.../build-dir/aarch64-apple-ios/src/deps/Img-c7767a3ba0b3d1d4" "-Wl,-dead_strip" "-nodefaultlibs" "-Wl,-no_uuid" "-Wl,-S" "-Wl,-dead_strip" "-Wl,-dead_strip_dylibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: ld: could not parse bitcode object file /.../build-dir/aarch64-apple-ios/src/deps/libcompiler_builtins-75a2186d30a4b1be.rlib[3](compiler_builtins-75a2186d30a4b1be.compiler_builtins.ab41fbc527b53a2f-cgu.0.rcgu.o): 'Invalid attribute group entry (Producer: 'LLVM21.1.0-rust-1.91.0-nightly' Reader: 'LLVM APPLE_1_1600.0.26.3_0')', using libLTO version 'LLVM version 16.0.0' in '/.../build-dir/aarch64-apple-ios/src/deps/libcompiler_builtins-75a2186d30a4b1be.rlib[3](compiler_builtins-75a2186d30a4b1be.compiler_builtins.ab41fbc527b53a2f-cgu.0.rcgu.o)'
          clang: error: linker command failed with exit code 1 (use -v to see invocation)

Invalid attribute group entry (Producer: 'LLVM21.1.0-rust-1.91.0-nightly' Reader: 'LLVM APPLE_1_1600.0.26.3_0')

Similar errors occurred on other targets too,

such as unix
Invalid attribute group entry (Producer: 'LLVM21.1.0-rust-1.91.0-nightly' Reader: 'LLVM 18.1.3'),

or Android
Unknown attribute kind (103) (Producer: 'LLVM21.1.0-rust-1.91.0-nightly' Reader: 'LLVM 19.0.1')

Add "-Clinker-plugin-lto=no" as workaround can fix this error temporarily.

It affects all cross build targets except windows targets.

[bjorn3]

Linker plugin LTO requires everyone to agree on the LLVM version. On macOS I'm not sure the XCode linker is able to use any LLVM version other than the Apple fork of LLVM, which is too old for rustc. Which linker are you using when linking for Linux? If you are using lld but not the lld version shipped with rustc (rust-lld) try using that one. Lld doesn't support linker plugins either and links against a single LLVM version, which if you got lld from your distro is going to be too old too. You can also use ld.bfd instead of lld. ld.bfd does actually support linker plugins and as such should work with the LLVM LTO linker plugin that rustc ships with.

[Wyvern]

The problem is: before rustc 1.91.0-nightly (f2824da98 2025-08-28) everything works normally, and I didn't have "-Clinker-plugin-lto=yes" option in my config.toml.

After daily toolchain update in CI the problem occurred, through error analysis I add "-Clinker-plugin-lto=no" as a workaround to prevent it.

By the way, I didn't use some other weird linkers, only on linux targets use rust builtin lld, other platforms use default linker as is.

[bjorn3]

I see. I assumed you did use -Clinker-plugin=lto=yes. Would you mind bisecting the regression? https://rust-lang.github.io/cargo-bisect-rustc/ may be helpful.

[Wyvern]

Through quick review of last day merge list, I found CFI: Make lto and linker-plugin-lto work the same for compiler_builtins #145368

Ref it as a hint.

[bjorn3]

cc @rcvalle