Unexpected f32 values for println and format macros with powerpc64le-unknown-linux-gnu target

[marcransome]

The problem

The println! and format! macros yield unexpected results for f32 primitive type values when cross compiling for powerpc64le-unknown-linux-gnu.

Configuration

• Toolchain: stable-x86_64-apple-darwin (rustc 1.58.1 (db9d1b20b 2022-01-20))
• Target: powerpc64le-unknown-linux-gnu

Example

fn main() {
    println!("f32: {:.1}", 1.0f32);
    println!("f64: {:.1}", 1.0f64);
}

Expected result:

f32: 1.0
f64: 1.0

Output of cross run --target powerpc64le-unknown-linux-gnu (note the incorrect value printed for f32):

f32: 0.0
f64: 1.0

Additional information

It appears that the version of QEMU used for powerpc64le-unknown-linux-gnu was pinned to 3.0.1 here as a fix for issue #313. The upstream issue has supposedly been fixed and released with QEMU 4.2.0, though I'm unable to confirm for certain if this is related to the issue above.

[Alexhuszagh]

This works as of 2f24bd4 (and likely much earlier).

cargo install cross --git https://github.com/cross-rs/cross
git clone https://github.com/Alexhuszagh/cross_issue644 && cd cross_issue644
cross run --target powerpc64le-unknown-linux-gnu

Which outputs:

    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `/linux-runner powerpc64le /target/powerpc64le-unknown-linux-gnu/debug/issue644`
f32: 1.0
f64: 1.0

The new Qemu version is 5.1.0, which fixes this and numerous other issues with floats on PowerPC architectures.