There's a PoC bootstrap for aarch64-linux now: https://github.com/NixOS/nixpkgs/pull/487398 To make this work, I had to tell gcc-15 that the host is musl-based. But in fact this breaks building glibc on i686 (but not on x86_64). I think this might be the frankenstein gcc problem? So I guess we need a glibc already built before we build a proper gcc targeting glibc

Extensive mode, which contains all the checks from fast mode and some additional checks for undefined behavior that incur relatively little overhead but aren’t security-critical. Production builds requiring a broader set of checks than fast mode should consider enabling extensive mode. The additional rigour impacts performance more than fast mode: we recommend benchmarking to determine if that is acceptable for your program.