On Wed, Feb 5, 2025 at 2:12 PM Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx> wrote: > > On Fri, Jan 31, 2025 at 5:05 PM Andrew Lunn <andrew@xxxxxxx> wrote: > > > > Floating point is banned within the kernel, except for in very narrow > > conditions, because the floating point registers are lazy saved on > > context switch. If the kernel uses the floating point registers, you > > can break user space in bad ways. > > > > I expect this has been discussed, since it is well known kernel > > restriction. Maybe go see what happened to that discussion within RfL? > > Yeah, it has been discussed, including in the last couple weeks in the > Rust Zulip due to the upcoming move to the aarch64 `softfloat` target > (the disallowing of disabling `neon` in the hardfloat one). > > Ideally, I think upstream Rust could perhaps give us a way to do > something like `-mgeneral-regs-only` or `-march=...+nofp` (in the form > GCC does it, i.e. a hard error if one even tries to use the floating > point types even within a function implementation, not just in > interfaces like in Clang), i.e. a way to avoid unintended use of > floating point facilities: > > https://godbolt.org/z/o1E5nrrzc > > Currently it is unclear what form that could take (e.g. whether a > `-nofloat` target could be possible, "disabling" the `f*` types, just > Clippy...). Seems like we already have a warning for it: warning: floating-point arithmetic detected --> /home/aliceryhl/rust-for-linux/rust/kernel/lib.rs:89:5 | 89 | a + b | ^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#float_arithmetic = note: requested on the command line with `-W clippy::float-arithmetic` > Cc'ing Catalin in case he wants to be in the loop, since I discussed > it with him recently. > > Cheers, > Miguel
