为什么gcc使用movl而不是push来传递函数参数？

注意这段代码：

#include <stdio.h>
void a(int a, int b, int c)
{
    char buffer1[5];
    char buffer2[10];
}

int main()
{
    a(1,2,3); 
}

在那之后 ：

gcc -S a.c

该命令显示了我们的汇编源代码。

现在我们可以看到在主函数中，我们从不使用“push”命令来推送参数 将a函数放入栈中。它使用“移动”代替

main:
 pushl %ebp
 movl %esp, %ebp
 andl $-16, %esp
 subl $16, %esp
 movl $3, 8(%esp)
 movl $2, 4(%esp)
 movl $1, (%esp)
 call a
 leave

为什么会发生这种情况？ 他们之间有什么区别？

这是什么海湾合作委员会手册不得不说一下：

-mpush-args
-mno-push-args
    Use PUSH operations to store outgoing parameters. This method is shorter and usually
    equally fast as method using SUB/MOV operations and is enabled by default. 
    In some cases disabling it may improve performance because of improved scheduling
    and reduced dependencies.

 -maccumulate-outgoing-args
    If enabled, the maximum amount of space required for outgoing arguments will be
    computed in the function prologue. This is faster on most modern CPUs because of
    reduced dependencies, improved scheduling and reduced stack usage when preferred
    stack boundary is not equal to 2. The drawback is a notable increase in code size.
    This switch implies -mno-push-args. 

显然-maccumulate-outgoing-args默认启用，覆盖-mpush-args。显式编译-mno-accumulate-outgoing-args确实恢复到PUSH方法，这里。

2019年更新：自 Pentium M 以来，现代 CPU 就具有高效的推送/弹出功能。
-mno-accumulate-outgoing-args（并使用推送）最终成为默认设置-mtune=generic2014 年 1 月。