Re: [PATCH 1/7] Fix function argument and return value locations

[Simon Marchi <simark@simark.ca>]

On 2020-05-25 5:32 p.m., Hannes Domani via Gdb-patches wrote:
> You're probably right, the thing is, I was only able to test complex float
> and complex double, because gdb doesn't like complex integral types:
> 
> complex int complex_int = 5 + 6i;
> 
> (gdb) p complex_int
> 'complex_int' has unknown type; cast it to its declared type
> (gdb) pt complex_int
> 'complex_int' has unknown type; cast it to its declared type
> 
> So I guess it should check for target-type float as well:
>        || (type->code () == TYPE_CODE_COMPLEX
>            && TYPE_TARGET_TYPE (type)->code () == TYPE_CODE_FLT))
> 
> Do many people use complex int, because I personally wouldn't have expected
> that this even exists.

Err right that doesn't make sense, let's use floats instead.  I see:


$ cat hello.c
#include <complex.h>

void other(float real, float imag);
void func (complex float n)
{
  other(creal(n), cimag(n));
}
$ x86_64-w64-mingw32-gcc hello.c -g3 -O0 -c
$ x86_64-w64-mingw32-objdump -d hello.o

hello.o:     file format pe-x86-64


Disassembly of section .text:

0000000000000000 <func>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   48 83 ec 20             sub    $0x20,%rsp
   8:   48 89 4d 10             mov    %rcx,0x10(%rbp)
   c:   f3 0f 10 45 14          movss  0x14(%rbp),%xmm0
  11:   f3 0f 5a c0             cvtss2sd %xmm0,%xmm0
  15:   f2 0f 5a c8             cvtsd2ss %xmm0,%xmm1
  19:   f3 0f 10 45 10          movss  0x10(%rbp),%xmm0
  1e:   f3 0f 5a c0             cvtss2sd %xmm0,%xmm0
  22:   f2 0f 5a c0             cvtsd2ss %xmm0,%xmm0
  26:   e8 00 00 00 00          callq  2b <func+0x2b>
  2b:   90                      nop
  2c:   48 83 c4 20             add    $0x20,%rsp
  30:   5d                      pop    %rbp
  31:   c3                      retq

Doesn't this suggest that the parameter gets passed through rcx?  I'm not saying you
are wrong, I'm just trying to understand how things work :).

Simon