Rust 1.99.1 point release fixes a missing wcslen symbol, an FFI bool miscompilation and a macOS linker problem
The Rust team published 1.99.1 to correct three regressions from earlier releases, including link errors on UEFI targets.
The Rust release team has published Rust 1.99.1, a point release that fixes three regressions found in earlier versions. It can be installed with rustup update stable.
The first fix adds a fallback wcslen function to compiler-builtins. An LLVM optimization pass can introduce calls to wcslen, and some targets had no copy of it available, which broke UEFI builds of projects using std.
The second fix concerns Rust functions that return bool through FFI on x86_64. The upper bits of the return register could be left unspecified, so a caller might see a value other than 0 or 1. The return type is again marked for zero-extension, as the ABI requires.
The third fix lets rust-lld find libLLVM on macOS when the compiler is started without the rustup proxy. Developers who hit any of these problems on 1.99.0 should update; the team also invites testing of the beta and nightly channels in CI.
Sources
- Announcing Rust 1.99.1official
Verified Oct 26, 2026 (official source). rustreleasetoolchain