Rust 1.99.1 fixes link errors, an FFI bool miscompilation and a rust-lld issue on macOS

The point release addresses three regressions from earlier versions, including UEFI targets that failed to link projects using std.

The Rust release team published Rust 1.99.1, a point release that fixes three regressions introduced in earlier versions. It can be installed with rustup update stable.

One fix adds a fallback wcslen function to the compiler-builtins library. An LLVM optimization pass can emit calls to that function, and some targets had no copy available, which caused link errors. UEFI targets were hit hardest, since projects using std could not build at all.

A second fix restores zero-extension for bool return values from Rust functions called over FFI on x86_64. Without it, callers could see raw values other than 0 or 1, because some bits of the return register were left unspecified.

The third fix gives rust-lld an rpath entry for the directory holding libLLVM.dylib, so the linker runs on macOS even when the compiler is invoked without the rustup proxy.

Developers on 1.99.0, especially those targeting UEFI, calling Rust from C over FFI, or building on macOS without rustup proxies, should update to 1.99.1. The team also invites testing on the beta and nightly channels in CI.

Sources

• Announcing Rust 1.99.1official

Verified Oct 24, 2026 (official source). rustreleasecompiler