On 09/16/2012 10:05 AM, phi gcc wrote:
> Pardon my naive question, I am newbe in x86 (32bit) architecture and I
> got hard time to find info on x86 procedure convention with GCC.
>
> The doc I found so far say that with __attribute__((fastcall)) it is
> possible to pass up to 2 long into regs ecx, edx.
>
> Yet looking at linux kernel code I got this on a piece of code.
>
> disass crash_kexec
> 0xc049a8c0 crash_kexec:
> ....
> 0x00000000c049a922 movl kexec_crash_image,%eax
> 0x00000000c049a927 calll machine_kexec
>
> The C code shows
> void crash_kexec(struct pt_regs *regs)
> {...
> machine_kexec(kexec_crash_image);
> }
>
> and machine_kexec() prolog shows
> 0xc042c2a0 machine_kexec:
> 0x00000000c042c2a0 pushl %ebp
> 0x00000000c042c2a1 pushl %edi
> 0x00000000c042c2a2 pushl %esi
> 0x00000000c042c2a3 pushl %ebx
> 0x00000000c042c2a4 movl %eax,%ebx
> 0x00000000c042c2a6 subl $0x2c,%esp
>
> With a save of eax (suposedly args0) into a callee save.
>
> So my question, does GCC under some circumstance does pass args0 into rax ?
GCC can call static functions in any way it likes, or it can inline them.
Calling conventions aren't relevant here: a static function isn't reachable
from any external caller.
Andrew.
