从内联 ASM (X64) 调用 printf

Question

我有这个代码:

#include <stdio.h>
#include <stdint.h>

int main(void){
    char *fmt = "%s";
    char *s = "Hello world!\n";

//gcc -m32 test.c
#ifdef __i386__
    int32_t ret;
    __asm__ __volatile__ (
        "push %1\n\t"
        "push %2\n\t"
        "movl $2, %%eax\n\t"
        "call printf\n\t"
        "movl %0, %%eax"
        : "=r" (ret)
        : "r" (s), "r" (fmt)
        :
    );
#endif

//gcc -m64 test.c
#ifdef __x86_64__
    int64_t ret;
    __asm__ __volatile__ (
        "push %1\n\t"
        "push %2\n\t"
        "movq $2, %%rax\n\t"
        "call printf\n\t"
        "movq %0, %%rax"
        : "=r" (ret)
        : "r" (s), "r" (fmt)
        :
    );
#endif

    return ret;
}

x86 版本按预期工作，但 x64 版本出现段错误。为什么会出现段错误？

Answer 1

64 位 ABI 使用寄存器(RDI、RSI、RDX、RCX、R8 和 R9)而不是堆栈来传递参数。所以代码应该是:

movl %2,%%rdi
movl %1,%%rsi
call printf
movq %0,%%rax