Unable to link code containing naked functions on ARM64 macOS with ThinLTO enabled #148307
Description
I have originally reported this issue in wasmtime repository and was redirected here: bytecodealliance/wasmtime#11957. I have tried to minimize the reproduction, but I failed to do so in reasonable time. The complexity of wasmtime crates is critical here. I would appreciate any hints that would help me minimize this.
Compiling Wasmtime 38.0.3 produces a linker error on ARM64 macOS when building with ThinLTO enabled. The error indicates that wasmtime_fiber_switch symbol is undefined during linking.
error: linking with `cc` failed: exit status: 1 | = note: "cc" "<426 object files omitted>" "/var/folders/8c/r_zrp9mj12xd414t08zrks940000gn/T/rustc2wYYXA/{libwasmtime-e843f7bbc21927d3,libzstd_sys-7eabaf414ee67d02,libwasmtime_internal_jit_debug-9043bb9a4e496da8}.rlib" "<sysroot>/lib/rustlib/aarch64-apple-darwin/lib/libcompiler_builtins-*.rlib" "-liconv" "-lSystem" "-lc" "-lm" "-arch" "arm64" "-mmacosx-version-min=11.0.0" "-L" "/Users/mk/Developer/software-mansion/scarb/linker-repro/wasmtime-only-test/target/release/build/wasmtime-15671f59b24bbe0f/out" "-L" "/Users/mk/Developer/software-mansion/scarb/linker-repro/wasmtime-only-test/target/release/build/zstd-sys-1ea01473940232bc/out" "-L" "/Users/mk/Developer/software-mansion/scarb/linker-repro/wasmtime-only-test/target/release/build/wasmtime-internal-jit-debug-2aaf81cce8508d62/out" "-o" "/Users/mk/Developer/software-mansion/scarb/linker-repro/wasmtime-only-test/target/release/deps/wasmtime_only_test-69cba5150eff8962" "-Wl,-dead_strip" "-nodefaultlibs" = note: some arguments are omitted. use `--verbose` to show all linker arguments = note: ld: warning: object file (/private/var/folders/8c/r_zrp9mj12xd414t08zrks940000gn/T/rustc2wYYXA/libwasmtime-e843f7bbc21927d3.rlib[2](242b1992def1ef0b-helpers.o)) was built for newer 'macOS' version (26.0) than being linked (11.0) ld: warning: object file (/private/var/folders/8c/r_zrp9mj12xd414t08zrks940000gn/T/rustc2wYYXA/libwasmtime_internal_jit_debug-9043bb9a4e496da8.rlib[2](db3b6bfb95261072-gdbjit.o)) was built for newer 'macOS' version (26.0) than being linked (11.0) Undefined symbols for architecture arm64: "wasmtime_internal_fiber::stackswitch::aarch64::wasmtime_fiber_switch::h0b241ee887e10750", referenced from: wasmtime_internal_fiber::unix::Suspend::switch::hfd4514b4efef3e13 in wasmtime_only_test-69cba5150eff8962.wasmtime-e843f7bbc21927d3.wasmtime.7e3b8021754df0c4-cgu.05.rcgu.o.rcgu.o ld: symbol(s) not found for architecture arm64 clang: error: linker command failed with exit code 1 (use -v to see invocation) What's important is that this issue only pops up with ThinLTO enabled. It didn't fail with either LTO disabled, set to FatLTO, or Wasmtime 37.
Steps to Reproduce
- Architecture: ARM64 (Apple Silicon)
- OS: macOS 26.0
- Rust: 1.90.0
- Wasmtime: 38.0.3
- Build Profile:
releasewithlto = "thin"
Cargo.toml:
[package] name = "linker-repro" version = "0.1.0" edition = "2021" [dependencies] wasmtime = "38" [profile.release] lto = "thin" src/main.rs:
fn main() { let engine = wasmtime::Engine::default(); println!("Engine created: {:?}", engine); }Build command:
cargo build --releaseThis will fail with the linker error shown above.
I think the wasmtime commit that triggers this regression is: bytecodealliance/wasmtime@3e9eca8
Meta
I have tested this reproduction on all stable+beta+nightly at the time of submitting this issue:
rustc --version --verbose:
rustc 1.90.0 (1159e78c4 2025-09-14) binary: rustc commit-hash: 1159e78c4747b02ef996e55082b704c09b970588 commit-date: 2025-09-14 host: aarch64-apple-darwin release: 1.90.0 LLVM version: 20.1.8 rustc 1.92.0-beta.1 (3b4dd9bf1 2025-10-28) binary: rustc commit-hash: 3b4dd9bf1410f8da6329baa36ce5e37673cbbd1f commit-date: 2025-10-28 host: aarch64-apple-darwin release: 1.92.0-beta.1 LLVM version: 21.1.3 rustc 1.93.0-nightly (292be5c7c 2025-10-29) binary: rustc commit-hash: 292be5c7c05138d753bbd4b30db7a3f1a5c914f7 commit-date: 2025-10-29 host: aarch64-apple-darwin release: 1.93.0-nightly LLVM version: 21.1.3