tgross35 wrote:
It seems like arguments aren't actually getting passed indirectly to libcalls.
Simple test program
```c
#include <stdint.h>
#include <stdio.h>
union ty128 {
struct { uint64_t hi, lo; } u64x2;
__float128 f128;
};
void f128_add(__float128 a, __float128 b) {
union ty128 cvt;
cvt.f128 = a * b;
printf("0x%016llx%016llx\n", cvt.u64x2.lo, cvt.u64x2.hi);
}
int main() {
__float128 fa, fb;
fa = 122134.345678901234;
fb = 78.9012345678901234;
f128_add(fa, fb);
}
```
Checking right before the call to `__multf3`. Built with GCC `rcx` points to a
return slot on the stack, `rdx` and `r8` point to the two float values
(0x400f... and 0x4005...):
```text
(gdb) x/2gx $rcx
0x7ffffcb30: 0x00000007ffffcbf0 0x00000007ffffcc85
(gdb) x/2gx $rdx
0x7ffffcb20: 0xb000000000000000 0x400fdd16587e6997
(gdb) x/2gx $r8
0x7ffffcb10: 0x8000000000000000 0x40053b9add3c0c73
```
Built using this patch, it looks like Clang is putting the float arguments in
`$rcx` and `$rdx` and not leaving a return slot pointer:
```text
(gdb) x/2gx $rcx
0x5ffe70: 0xb000000000000000 0x400fdd16587e6997
(gdb) x/2gx $rdx
0x5ffe60: 0x8000000000000000 0x40053b9add3c0c73
(gdb) x/2gx $r8
0x622720: 0x0000000000622988 0x00000000006229a7
```
Is libcall ABI handled elsewhere?
https://github.com/llvm/llvm-project/pull/115052
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