regression with LTO + musl + build-std

[jsen-]

since nightly-2025-08-29 the combination of following factors leads to a compilation error:

• toolchain x86_64-unknown-linux-gnu
• LTO enabled (both thin and fat lead to failure)
• cargo -Zbuild-std=std flag is used
• target x86_64-unknown-linux-musl

Code

I tried this code:

fn main() {}

cargo.toml:

[package]
name = "repro"
version = "0.1.0"
edition = "2024"

[profile.dev]
lto = "fat"

I expected to see this happen:

$ cargo +nightly-2025-08-28-x86_64-unknown-linux-gnu build -Zbuild-std=std --target x86_64-unknown-linux-musl
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.03s

Instead, this happened:

$ cargo +nightly-2025-08-29-x86_64-unknown-linux-gnu build -Zbuild-std=std --target x86_64-unknown-linux-musl
   Compiling repro v0.1.0 ($DIR)
error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "-m64" "<sysroot>/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained/rcrt1.o" "<sysroot>/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained/crti.o" "<sysroot>/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained/crtbeginS.o" "<68 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "-lunwind" "-lc" "$DIR/target/x86_64-unknown-linux-musl/debug/deps/libcompiler_builtins-c7f4fcb50b8f358d.rlib" "-L" "/tmp/rustckKscQc/raw-dylibs" "-Wl,-Bdynamic" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-nostartfiles" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-musl/lib" "-o" "$DIR/target/x86_64-unknown-linux-musl/debug/deps/repro-0da546c4af9fdcc4" "-Wl,--gc-sections" "-static-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs" "-fuse-ld=lld" "<sysroot>/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained/crtendS.o" "<sysroot>/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained/crtn.o"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: ld.lld: error: $DIR/target/x86_64-unknown-linux-musl/debug/deps/libcompiler_builtins-c7f4fcb50b8f358d.rlib(compiler_builtins-c7f4fcb50b8f358d.compiler_builtins.d1b674884d9f97b8-cgu.0.rcgu.o): Invalid record
          collect2: error: ld returned 1 exit status
          

error: could not compile `repro` (bin "repro") due to 1 previous error

Version it worked on

It most recently worked on: nightly-2025-08-28

Version with regression

rustc --version --verbose:

$ cargo +nightly-2025-08-29-x86_64-unknown-linux-gnu rustc -- --version --verbose 
   Compiling repro v0.1.0 ($DIR)
rustc 1.91.0-nightly (f2824da98 2025-08-28)
binary: rustc
commit-hash: f2824da98d44c4a4e17bf39eb45103c8fc249117
commit-date: 2025-08-28
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.0

I'm not sure whether this should rather be reported in the repository of cargo. If that's so I can create the issue there instead.

[jieyouxu]

Since this requires -Zbuild-std
@rustbot transfer cargo

[jieyouxu]

@rustbot label: +S-triage

[weihanglo]

Can you confirm that nightly-2025-08-28 is good?

[ehuss]

@jieyouxu I don't think this should have been transferred. Cargo does not have any control over linking.

I believe this regressed via #145368. cc @rcvalle @dianqk

[jieyouxu]

Ah right, sorry.
@rustbot transfer rust