Cannot build WASM target on freebsd: 'errno.h' file not found

[AMDmi3]

Summary

This broke somewhere after 2026-08-20 and 2026-08-30. Unfortunately, I cannot pinpoint exact broken version as versions right after that suffer from unrelated breakages.

Command used

After upding FreeBSD port lang/rust-nightly to the latest version (2026-08-20 with bootstraps 2026-08-28) , make -C /usr/ports/lang/rust-nigthly install

Expected behaviour

Successful build.

Actual behaviour

profiler_builtins fail to build for wasm target:

   Compiling profiler_builtins v0.0.0 (/work/usr/ports/lang/rust-nightly/work/rustc-nightly-src/library/profiler_builtins)
     Running `/work/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/stage1-std/dist/build/profiler_builtins/72636cab5acea68e/out/build_script_build`
warning: profiler_builtins@0.0.0: /work/usr/ports/lang/rust-nightly/work/rustc-nightly-src/src/llvm-project/compiler-rt/lib/profile/GCDAProfiling.c:29:10: fatal error: 'errno.h' file not found
warning: profiler_builtins@0.0.0:    29 | #include <errno.h>
warning: profiler_builtins@0.0.0:       |          ^~~~~~~~~
warning: profiler_builtins@0.0.0: 1 error generated.
error: failed to run custom build command for `profiler_builtins v0.0.0 (/work/usr/ports/lang/rust-nightly/work/rustc-nightly-src/library/profiler_builtins)`

Notably, WASM target can be disabled in FreeBSD port, and rust builds fine if it is.

Bootstrap configuration (bootstrap.toml)

[build]
build-dir="/usr/ports/lang/rust-nightly/work/_build"
build-stage=2
doc-stage=2
test-stage=2
vendor=true
extended=true
python="/usr/local/bin/python3.12"
docs=false
verbose=2
profiler=true
target=["x86_64-unknown-freebsd","wasm32-unknown-unknown"]
cargo="/usr/ports/lang/rust-nightly/work/bootstrap/bin/cargo"
rustc="/usr/ports/lang/rust-nightly/work/bootstrap/bin/rustc"
tools=["analysis","cargo","clippy","rust-analyzer","rustdoc","rustfmt","src","miri","cargo-miri"]
ccache=false
[install]
prefix="/usr/ports/lang/rust-nightly/prefix"
sysconfdir="/usr/ports/lang/rust-nightly/prefix/etc"
[rust]
channel="nightly"
default-linker="cc"
deny-warnings=false
verbose-tests=true
download-rustc=false
lld=true
lto="thin"
remap-debuginfo=true
[llvm]
download-ci-llvm=false
clang=true
thin-lto=true
ninja=true
[target.x86_64-unknown-freebsd]
ar="ar"
cc="cc"
cxx="c++"
linker="cc"
[target.wasm32-unknown-unknown]
ar="ar"
cc="/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/llvm/bin/clang"
cxx="/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/llvm/bin/clang++"
linker="/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/llvm/bin/clang"
[dist]
compression-formats=["xz"]
src-tarball=false

Operating system

FreeBSD 15.1

HEAD

cea272fa356e94bd2ee2cadf376630aa0683867a

Additional context

Full build log: https://people.freebsd.org/~amdmi3/rust.log
For reference, successful log for older version, 2026-08-20: https://people.freebsd.org/~amdmi3/rust20.log

[bjorn3]

Your clang build may not have the right headers to build C code for wasm. You could set build.optimized-compiler-builtins to false to skip building the C code here.

[AMDmi3]

Where do these headers come from, are these not bundled? How to point the build to them? Has something changed between august 20 and 28 so this is now relevant?

You could set build.optimized-compiler-builtins to false to skip building the C code here.

Can this be set per target?

[bjorn3]

Where do these headers come from, are these not bundled?

It looks like a regular libc header that is supposed to be part of your C toolchain.

Has something changed between august 20 and 28 so this is now relevant?

If it broke on August 5th, I would have said that the update to LLVM 23 may be to blame. But for the range 20-28, #161260 may be relevant. Or #161466.

Can this be set per target?

Yes, target."wasm32-unknown-unknown".optimized-compiler-builtins.

Looking closer at the error message, I notice now it says profiler-builtins, not compiler-builtins as I expected. profiler-builtins is not going to work without libc and wasm32-unknown-unknown doesn't have a libc, so it shouldn't be building profiler-builtins. Does target."wasm32-unknown-unknown".profiler = false help? That should be the default already though.

@Kobzol did anything recently change on the bootstrap side around profiler runtimes?

[Kobzol]

I don't recall anything. My first guess would be the cc update.

[AMDmi3]

Does target."wasm32-unknown-unknown".profiler = false help?

Yes this helps, thank you!

I wonder why it built before though, old log has the same calls like Running /work/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/stage1-std/dist/build/profiler_builtins/9ea7f21d5007e55f/out/build_script_build. Want me to gather more input?