是的,看來GCC將扔掉的 「printf(」 %S \ n」, BUFF)」而代以 「看跌期權()」 在其位:
vi tmp.c =>
#include <stdio.h>
#include <string.h>
int
main(int argc, char **argv)
{
char buf[128];
if(argc < 2)
return 1;
strcpy(buf, argv[1]);
printf("%s\n", buf);
return 0;
}
$ GCC -S -Wall -pedantic tmp.c 更少tmp.s =>
.file "tmp.c"
.text
.globl main
.type main, @function
main:
leal 4(%esp), %ecx
andl $-16, %esp
pushl -4(%ecx)
pushl %ebp
movl %esp, %ebp
pushl %ecx
subl $148, %esp
movl %ecx, -140(%ebp)
movl -140(%ebp), %eax
cmpl $1, (%eax)
jg .L2
movl $1, -136(%ebp)
jmp .L4
.L2:
movl -140(%ebp), %edx
movl 4(%edx), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, 4(%esp)
leal -132(%ebp), %eax
movl %eax, (%esp)
call strcpy
leal -132(%ebp), %eax
movl %eax, (%esp)
call puts
movl $0, -136(%ebp)
.L4:
movl -136(%ebp), %eax
addl $148, %esp
popl %ecx
popl %ebp
leal -4(%ecx), %esp
ret
.size main, .-main
.ident "GCC: (GNU) 4.1.2 20080704 (Red Hat 4.1.2-48)"
.section .note.GNU-stack,"",@progbits
是否可以通過寄存器呢? – dasblinkenlight
也許它優化了一個sys_write系統調用? –
Thanx for sharing - 我從來不知道gcc會這麼做(用「printf()」替代「puts()」)。但顯然它可以 - 並且:) – paulsm4