bootstrap: add an rpath to LLVM library for LLVM tools

[danieljhkim]

Closes #164063 by adding rpath to the LLVM tool executables on both Linux and macOS, using the same approach as Lld::run.

This PR is now written by a human, resubmitting #164064 which was diagnosed and written by Claude.

Validation:

macOS

❯ otool -l ~/workspace/repos/rust/build/aarch64-apple-darwin/llvm/bin/llvm-objcopy | grep -A2 LC_RPATH
          cmd LC_RPATH
      cmdsize 40
         path @loader_path/../../../ (offset 12)
--
          cmd LC_RPATH
      cmdsize 32
         path @loader_path/../lib (offset 12)

❯ otool -L build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib
build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib:
        @rpath/libLLVM.dylib (compatibility version 1.0.0, current version 23.1.3)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1359.0.0)
        /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.12)
        /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 2200.27.0)

linux

readelf -d build/x86_64-unknown-linux-gnu/llvm/bin/llvm-objcopy | grep RUNPATH
 0x000000000000001d (RUNPATH)            Library runpath: [$ORIGIN/../../../:$ORIGIN/../lib:$ORIGIN/../lib/x86_64-unknown-linux-gnu]

[rustbot]

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

[rustbot]

Thanks for the pull request, and welcome! The Rust Project has assigned @Mark-Simulacrum (or someone else) to review your changes, you should hear from them (or someone else) within the next two weeks.

Please see the contribution instructions and our LLM policy for more information.

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: bootstrap
• bootstrap expanded to 6 candidates
• Random selection from Mark-Simulacrum, clubby789, jieyouxu

[Kobzol]

r? kobzol

Thanks for the PR. Two remarks:

• We now have the same logic duplicated on three places (OmpOffload, Lld and Llvm). Could you please extract it to a shared function that takes a builderand atarget`? The function should only be called if we link LLVM dynamically.
• Won't the linker flags be also applied to libLLVM.so itself? Have you tried building it on Linux and running lld on it - if yes, what does it print?

[danieljhkim]

r? kobzol

Thanks for the PR. Two remarks:

• We now have the same logic duplicated on three places (OmpOffload, Lld and Llvm). Could you please extract it to a shared function that takes a builderand atarget`? The function should only be called if we link LLVM dynamically.
• Won't the linker flags be also applied to libLLVM.so itself? Have you tried building it on Linux and running lld on it - if yes, what does it print?

@Kobzol thanks for the review.

I have updated the PR to use a common helper (llvm_lib_rpath) as requested.

The fix pushes rpath into ldflags.exe, which only applies when linking executables, and libLLVM.so is linked with the shared-library flags. Below are verifications I ran on linux.

$ readelf -d build/x86_64-unknown-linux-gnu/llvm/bin/llvm-objcopy | grep RUNPATH
 0x000000000000001d (RUNPATH)            Library runpath: [$ORIGIN/../../../:$ORIGIN/../lib:$ORIGIN/../lib/x86_64-unknown-linux-gnu]

$ readelf -d build/x86_64-unknown-linux-gnu/llvm/lib/libLLVM.so | grep RUNPATH
 0x000000000000001d (RUNPATH)            Library runpath: [$ORIGIN/../lib:$ORIGIN/../lib/x86_64-unknown-linux-gnu]

$ ldd build/x86_64-unknown-linux-gnu/llvm/lib/libLLVM.so
        linux-vdso.so.1 (0x000072d83e4ea000)
        libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x000072d834200000)
        libm.so.6 => /usr/lib/x86_64-linux-gnu/libm.so.6 (0x000072d8344da000)
        libgcc_s.so.1 => /usr/lib/x86_64-linux-gnu/libgcc_s.so.1 (0x000072d8344ac000)
        libc.so.6 => /usr/lib/x86_64-linux-gnu/libc.so.6 (0x000072d833e00000)
        /lib64/ld-linux-x86-64.so.2 (0x000072d83e4ec000)

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[Kobzol]

Thanks!

@bors r+

[rust-bors]

📌 Commit 46395c5 has been approved by Kobzol

It is now in the queue for this repository.