This snipped of code:
void f(double *a, double *b, void *c)
{
a[0]*abs(3);
}
generates following object code:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 81 ec 20 00 00 00 sub $0x20,%rsp
b: 48 89 7d f8 mov %rdi,-0x8(%rbp)
f: 48 89 75 f0 mov %rsi,-0x10(%rbp)
13: 48 89 55 e8 mov %rdx,-0x18(%rbp)
17: 48 8b 45 f8 mov -0x8(%rbp),%rax
1b: 48 89 45 e0 mov %rax,-0x20(%rbp)
1f: b8 03 00 00 00 mov $0x3,%eax
24: 48 89 c7 mov %rax,%rdi
27: b8 00 00 00 00 mov $0x0,%eax
2c: e8 fc ff ff ff callq 2d <f+0x2d>
31: f2 0f 2a c0 cvtsi2sd %eax,%xmm0
35: 8b 45 e0 mov -0x20(%rbp),%eax
38: f3 0f 7e c8 movq %xmm0,%xmm1
3c: 48 8b 5d e0 mov -0x20(%rbp),%rbx
40: f3 0f 7e 03 movq (%rbx),%xmm0
44: f2 0f 59 c1 mulsd %xmm1,%xmm0
48: c9 leaveq
49: c3 retq
As you can see the rbx register gets clobbered by the load at address
0x3c. I'm not at all an expert on ABIs but I think the rbx needs to be
preserved across function calls and this is causing problems further
downstream in my code.
Any chance this could be easily addressed? If the rbx could be excluded
from registers used for general operations within functions that would
probably be sufficient for my purposes...
Best,
Bojan
(I am on git revision ID 83d57c06f406bbb7198b1683fc522f23251b5f57)