Extended Description

This bug has been originally discovered by Michael Karcher. Filling the bug on behalf of them.

As noted while filing a bug on rustc because rustc does not correctly implement the Sparc64 ABI regarding floating point fields of "small" structures, I stumbled across a difference between gcc an clang, as shown in rust-lang/rust#57103 (the important piece is quoted below):

struct str3 {
float f; // passed in most-significant half of %o0 (gcc) or in %f0 (clang)
int i; // passed in least-significant half of %o0
} attribute((packed));

Without attribute((packed)), clang, gcc and the ABI standard agree to pass f in %f0. The ABI standard doesn't contain anything about packed structures, so I don't see a way to decide whether gcc or clang is right. I report a bug on both products to raise awareness.