Link errors when compiling for i386 with +soft-float

[roblabla]

It appears that since #61408, rust now requires fminf and fmaxf functions to be present when compiling for i386 with +soft-float (using a custom target JSON). However, compiler-builtins only expose those functions for some targets, which don't include x86.

Maybe compiler-builtins should include a target-feature = "soft-float" in the list of conditions to enable the math module?

[roblabla]

Going to be working on this. Anyone know a way to get the list of calls LLVM can lower instructions to for soft-float ops?

Nevermind, went through the intrinsics in std::intrinsics and tested them one after the other.

[bugadani]

This issue also affects thumbv7em-none-eabihf. Note the fminf call here: godbolt.

Build fails with note: rust-lld: error: undefined symbol: fmaxf

At least the workaround is simple enough:

#[no_mangle]
fn fminf(a: f32, b: f32) -> f32 {
    if a < b {
        a
    } else {
        b
    }
}

#[no_mangle]
fn fmaxf(a: f32, b: f32) -> f32 {
    if a > b {
        a
    } else {
        b
    }
}

[TheMatten]

Same problem seems to appear on x86_64-unknown-uefi.

[phip1611]

Since yesterday I'm investigating a similar bug and finally came to this issue just now. Maybe my issue and this one are linked (at least partially). I'm getting a similar error response when compiling a certain library for a x86_64 bare-metal target with +soft-float

My issue on Rust: #92760
My minimal reproducible error repo: https://github.com/phip1611/rust-llvm-bug-20220112-minimal-example/blob/main/README.md

The workaround from @bugadani solves the build problems.