linking fails with -Cdebuginfo=2

[matthiaskrgr]

I tried this code:

extern "C" {
    static _dispatch_queue_attr_concurrent: [u8; 0];
}

fn main() {
let x: &[u8; 0] =
    unsafe { &_dispatch_queue_attr_concurrent };
}

This code compiles and "runs" as with ``. -Cdebuginfo=1 but with `-Cdebuginfo=2` we get a linking error which seems a bit surprising:

warning: unused variable: `x`
 --> link.rs:6:5
  |
6 | let x: &[u8; 0] =
  |     ^ help: if this is intentional, prefix it with an underscore: `_x`
  |
  = note: `#[warn(unused_variables)]` on by default

error: linking with `cc` failed: exit status: 1
  |
  = note: "cc" "-m64" "/tmp/rustcERfmJd/symbols.o" "link.link.6e34ec64-cgu.0.rcgu.o" "link.link.6e34ec64-cgu.1.rcgu.o" "link.link.6e34ec64-cgu.2.rcgu.o" "link.link.6e34ec64-cgu.3.rcgu.o" "link.link.6e34ec64-cgu.4.rcgu.o" "link.34m5sv5uyn5dnfd3.rcgu.o" "-Wl,--as-needed" "-L" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-4393e7d07259b8a4.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-e13cbb326bcd01a4.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-13ac6af5403a52c8.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-a7b8febdd2acb289.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-343513f0726f71ed.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-8f833d900bfb98aa.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-e97a7960ca6216c8.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-683fb35093a61fcc.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-f943c2d34bd4b56d.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-72ce2aaa649404e0.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-ac5d08ad5339e92e.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-dacfda262d5656fb.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-e2056a834ba0712c.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-a60649c148c6e2db.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-3e961d059b9bcde7.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-20f26f875d0170e2.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-522518611024dce5.rlib" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-05898138a596088a.rlib" "-Wl,--end-group" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-5b83a1df856cf582.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "link" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro,-znow" "-nodefaultlibs"
  = note: /usr/bin/ld: link.link.6e34ec64-cgu.2.rcgu.o: in function `link::main':
          /tmp/link.rs:7: undefined reference to `_dispatch_queue_attr_concurrent'
          collect2: error: ld returned 1 exit status

  = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

error: aborting due to previous error; 1 warning emitted

Meta

rustc --version --verbose:

rustc 1.65.0-nightly (c07a8b4e0 2022-08-26)
binary: rustc
commit-hash: c07a8b4e09f356c7468b69c50cac7fc5b5000b8a
commit-date: 2022-08-26
host: x86_64-unknown-linux-gnu
release: 1.65.0-nightly
LLVM version: 15.0.0

bjorn3 on zulip

I would guess the reference to _dispatch_queue_attr_concurrent gets optimized away when there is no debuginfo for locals, suppressing the linker error.

[bjorn3]

Copying from zulip:

I would guess the reference to _dispatch_queue_attr_concurrent gets optimized away when there is no debuginfo for locals, suppressing the linker error.

[matthiaskrgr]

Closing again as per comment: https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/debuginfo.3D2.20breaks.20linking
🙃