1.65.0 fails to build on powerpc

[pkubaj]

1.64.0 built fine.
On powerpc-unknown-freebsd:

  = note: /usr/local/bin/ld.bfd: /wrkdirs/usr/ports/lang/rust/work/_build/powerpc-unknown-freebsd/stage0-rustc/powerpc-unknown-freebsd/release/deps/librustc_driver-95f1e4ba1a525000.so: undefined reference to `__atomic_load_8'
          /usr/local/bin/ld.bfd: /wrkdirs/usr/ports/lang/rust/work/_build/powerpc-unknown-freebsd/stage0-rustc/powerpc-unknown-freebsd/release/deps/librustc_driver-95f1e4ba1a525000.so: undefined reference to `__atomic_store_8'
          cc: error: linker command failed with exit code 1 (use -v to see invocation)

Probably related to LLVM upgrade.

[apiraino]

probably related to #103949 (different compile target but seemingly same symptoms).

Assigning same priority for the time being (Zulip discussion).

@rustbot label -I-prioritize +P-low

[nikic]

What does llvm-config --system-libs report? For cross-compiled builds we link libatomic here:

rust/compiler/rustc_llvm/build.rs

Line 248 in b7b7f27

|| target.starts_with("powerpc-")

But I assume you're using a native build?

[pkubaj]

root@powerpc-131-rust:/wrkdirs/usr/ports/lang/rust/work/_build/powerpc-unknown-freebsd/llvm/build/bin # ./llvm-config --system-libs
-lrt -lexecinfo -lpthread -lm -lz

FreeBSD doesn't have libatomic. LLVM is used in the base system, libatomic is GCC's component.

[pkubaj]

And yes, I build natively.

[nikic]

FreeBSD doesn't have libatomic. LLVM is used in the base system, libatomic is GCC's component.

If FreeBSD doesn't have libatomic, what library provides atomic libcalls instead? I found https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=230888 which makes it sound like these are supposed to be provided by compiler-rt (which is super suspicious, because __atomic builtins must be provided by a shared object with a globally shared mutex, not a static library).

In any case, this sounds like an issue in FreeBSD, not something that can/should be addressed on the Rust/LLVM side.

[pkubaj]

Yes, compiler_rt is used. Is it possible to disable generating those atomic calls?

[pkubaj]

I succeeded to build after installing gcc, adding appriopriate -L flag to RUSTFLAGS and modifying compiler/rustc_llvm/build.rs to always add -latomic and -lz (that was also necessary) on powerpc (not just for crosscompiling).

[apiraino]

@pkubaj do you consider this issue as resolved? If yes, can you close it? I understand you had to manually patch rustc to compile the target. Do you think that your patch would be useful for a PR upstream in rustc?

thanks @nikic for the support