Fails to build when linking with lld

[Kmeakin]

The unwind-sys crate fails to build when using lld as the linker:

RUSTFLAGS='-Clink-args=-fuse-ld=lld' cargo t --all-features produces a linker error:

          ld.lld: error: /usr/lib/x86_64-linux-gnu/libunwind-ptrace.so: undefined reference to lzma_stream_buffer_decode [--no-allow-shlib-undefined]
          ld.lld: error: /usr/lib/x86_64-linux-gnu/libunwind-ptrace.so: undefined reference to lzma_index_uncompressed_size [--no-allow-shlib-undefined]
          ld.lld: error: /usr/lib/x86_64-linux-gnu/libunwind-ptrace.so: undefined reference to lzma_index_end [--no-allow-shlib-undefined]
          ld.lld: error: /usr/lib/x86_64-linux-gnu/libunwind-ptrace.so: undefined reference to lzma_index_buffer_decode [--no-allow-shlib-undefined]
          ld.lld: error: /usr/lib/x86_64-linux-gnu/libunwind-ptrace.so: undefined reference to lzma_stream_footer_decode [--no-allow-shlib-undefined]
          ld.lld: error: /usr/lib/x86_64-linux-gnu/libunwind-ptrace.so: undefined reference to lzma_index_size [--no-allow-shlib-undefined]
          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: could not compile `unwind-sys` due to previous error

Your crate seems to rely on some GNU ld behaviour that the lld team are unwilling to replicate (llvm/llvm-project#54700).

I suggest this can be fixed by adding a cargo:rustc-link-lib=lzma directive to your build.rs build script.

[sfackler]

The build script relies on pkg-config for its linker configuration. You should file this issue on the libunwind project (or the packager that created your libunwind binaries): https://github.com/sfackler/rstack/blob/master/unwind-sys/build.rs#L11

[Kmeakin]

libunwind.pc includes -llzma in its Libs.private, which is only added to the linker args if pkg-config is called with the --static flag.

The solution is to replace
let library = pkg_config::probe_library(lib).unwrap();
with
let library = pkg_config::Config::new().statik(true).probe(lib).unwrap();
in build.rs.

[sfackler]

But you're not statically linking to libunwind - the linker error references libunwind-ptrace.so which is a dynamic library. libunwind-ptrace.so should internally declare its dependency on liblzma. It appears that that may not be the case which would be either a bug in the libunwind project or a bug in whatever built your libunwind binaries.

[cameron-martin]

Looks like this is the problem: libunwind/libunwind#586

However, libunwind is still on 1.6.2 on Ubuntu 22.04.

Would you not be up for manually adding an extra linker flag via a cargo directive, until 1.8.0 propagates through the distros?