--- Ed L Cashin <ecashin@uga.edu> wrote:
> Hi. That sounds like a question about the C
> language, but assuming
> that you only care about gcc (since this is
> kernelnewbies), why not
> just check and see?
>
> ecashin@marblerye tmp$ cat test.c
> #include <stdio.h>
>
> long long f(void)
> {
> long long i = 0x0123456789abcdefLL;
>
> return i;
> }
>
> int main(void)
> {
> long long i = f();
>
> printf("0x%Lx\n", i);
> return 0;
> }
The assembly equivalent of this code is
enlightening. 64 bit values are returned through the
%eax and %edx registers rather than through %eax
alone. Relevant portions are attached..
.globl f
.type f,@function
f:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
movl $-1985229329, -8(%ebp)
movl $19088743, -4(%ebp)
movl -8(%ebp), %eax <--------- copy to eax
movl -4(%ebp), %edx <--------- and edx to
return it
leave
ret
----------
.globl main
.type main,@function
main:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
andl $-16, %esp
movl $0, %eax
subl %eax, %esp
call f
movl %eax, -8(%ebp)<--------- take up the
movl %edx, -4(%ebp)<--------- return value
subl $4, %esp
pushl -4(%ebp)
pushl -8(%ebp)
pushl $.LC0
call printf
--------
=====
Regards,
Kiran Kumar Immidi
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