Skip to content

musl staticlib builds include all of the musl symbols #65760

Closed
Closed
musl staticlib builds include all of the musl symbols#65760
Labels
A-linkageArea: linking into static, shared libraries and binariesC-bugCategory: This is a bug.O-muslTarget: The musl libcT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

Description

@Twey
Twey
opened on Oct 24, 2019

Observed Behaviour

If I produce a simple staticlib crate for the x86_64-unknown-linux-musl target, I get a .a file that includes all the symbols from musl, including standard libc symbols like (for example) readlink. This makes it impossible to link this library into a C program that links against libc itself (or another Rust staticlib) as the linker will fail with duplicate symbol errors.

Reproduction

A test repository is at https://github.com/Twey/musl-staticlib-test, along with a Nix description of the relevant build environment for those so inclined. You can execute rustc -omusl-staticlib-test.a --target=x86_64-unknown-linux-musl --crate-type=staticlib lib.rs to get a library, and use a tool such as nm to view the symbols in the resulting binary. For example:

[twey@uruz:/tmp/musl-staticlib-test]$ nm musl_staticlib_test.a | grep readlink
                 U readlink
0000000000000000 T _ZN3std3sys4unix2fs8readlink17h4d68afd72996b214E
                 U readlink
readlink.lo:
0000000000000000 T readlink
readlinkat.lo:
0000000000000000 T readlinkat
                 U readlink

Expected Behaviour

Normally, static libraries for consumption by C, like rlibs, contain only symbols from the project itself, not symbols from dependencies. Certainly symbols from libc should never make it into the binary, as these will always conflict.

For example, here's libev, also built statically against musl:

[twey@uruz:/tmp/musl-staticlib-test]$ nm /nix/store/6r9z7a007vrla17paac35c968fmbzilq-libev-4.27-x86_64-unknown-linux-musl/lib/libev.a | grep readlink
[twey@uruz:/tmp/musl-staticlib-test]$

Activity

  1. jonas-schievink
    added
    A-linkageArea: linking into static, shared libraries and binaries
    C-bugCategory: This is a bug.
    O-muslTarget: The musl libc
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    on Oct 24, 2019

  2. aidanhs commented on Oct 24, 2019

    @aidanhs
    aidanhs
    on Oct 24, 2019
    Contributor

    The culprit is likely https://github.com/gnzlbg/libc/blob/e07cd949b0f5f30c009066b8c074ae32afd7feed/src/unix/mod.rs#L299-L305, where musl libc is unconditionally statically linked in when including the rust stdlib with "crt-static".

    When working with @Twey on this, our general observation was that:

    • it's not a good idea to put libc in a staticlib
    • it's not a good idea to put libc in a cdylib
    • it is a good idea for musl static linking to put musl libc in a binary

    Unfortunately, the first is not handled correctly by Rust. The right way to solve this for staticlibs is likely to just not link to libc at all - the symbols will remain undefined (as they should) and can be filled out in the actual link later.

    Unfortunately there's no way (that I'm aware of) to switch a cfg based on the final "kind of thing" being linked/produced by Rust, i.e. "if this is a staticlib then please don't link libc statically". And I do think it has to be a special case for libc - it is entirely reasonable to want to be able to bundle staticlibs inside each other in general.

    In an interesting twist of fate, setting -crt-static 'fixes' it...even though this attempts to link against libc dynamically. I believe the reason this works (and, as far as I can tell, the only reason building glibc staticlibs works at all) is because dylibs are ignored when creating a staticlib (without a warning afaict, contrary to the comment in the code) - https://github.com/rust-lang/rust/blob/3f2ae44/src/librustc_codegen_ssa/back/link.rs#L402-L403.

  3. mati865 commented on Oct 24, 2019

    @mati865
    mati865
    on Oct 24, 2019
    Member

    @aidanhs there was an attempt to do it, detailed discussion is available at rust-lang/libc#1327

  4. petrochenkov commented on May 16, 2020

    @petrochenkov
    petrochenkov
    on May 16, 2020
    Contributor

    Posted a plan for the fix in #72274.

  5. Noratrieb commented on Aug 2, 2025

    @Noratrieb
    Noratrieb
    on Aug 2, 2025
    Member

    It looks like this was fixed in #72274. I manually verified that a musl staticlib does no longer define libc symbols.

  6. Noratrieb
    closed this as completedon Aug 2, 2025
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Metadata

Metadata

Assignees

No one assigned

    Labels

    A-linkageArea: linking into static, shared libraries and binariesC-bugCategory: This is a bug.O-muslTarget: The musl libcT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

    Type

    No type

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions