https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105932
Bug ID: 105932
Summary: Small structures returned incorrectly in i386
Microsoft ABI
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Keywords: ABI, wrong-code
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: josephcsible at gmail dot com
Target Milestone: ---
Consider this C code:
struct foo {
int x, y;
};
extern int x, y;
struct foo f(void) {
struct foo rv;
rv.x = x;
rv.y = y;
return rv;
}
When compiled with "-O2 -m32 -mabi=ms", it compiles to this:
f:
movd x, %xmm0
movl 4(%esp), %eax
movd y, %xmm1
punpckldq %xmm1, %xmm0
movq %xmm0, (%eax)
ret
Which expects to be passed a hidden parameter to hold the address of the return
value. But in the i386 Microsoft ABI, that's not how returns work for POD types
that are 64 bits or smaller. Here's what it should compile to instead:
f:
movd x, %eax
movd y, %edx
ret
