在x86_64 linux上的C程序中进行内联汇编 [英] Inline assembly in C program on x86_64 linux
问题描述
我在linux x86_64上构建了一个用C和内联汇编编写的简短程序.应该将一个字符串写入stdout.我在互联网上的一篇文章中找到了它:
I've built a short program written on C and inline assembly on my linux x86_64. It is supposed to write a string to stdout. I found it in an article on the internet:
int write_call( int fd, const char * str, int len ){
long __res;
__asm__ volatile ( "int $0x80":
"=a" (__res):"0"(__NR_write),"b"((long)(fd)),"c"((long)(str)),"d"((long)(len)) );
return (int) __res;
}
void do_write( void ){
char * str = "Paragon output string.\n";
int len = strlen( str ), n;
printf( "string for write length = %d\n", len );
n = write_call( 1, str, len );
printf( "write return : %d\n", n );
}
int main( int argc, char * argv[] ){
do_write();
return EXIT_SUCCESS;
}
但是在我运行它时,它无法正常工作,从而产生输出
But as I run it, it works incorrectly, making output
写回信:-14"
"write return : -14"
如果我在32位linux上构建并运行它,它将达到预期的效果.
If I build and run it on 32-bit linux it does what is expected.
经过研究,我发现指令"int $ 0x80"是x86指令,如果在x86_64上调用,则会截断寄存器中的参数.
After some research I fount out that instruction "int $0x80" is a x86 instruction and truncates arguments in registers if called on x86_64.
但是我找不到x86_64体系结构的"int $ 0x80"的适当替代.我的组装经验为零.
But I couldn't find a proper substitution of "int $0x80" for x86_64 architecture. I have zero experience in assembly.
我应该用什么代替"int $ 0x80"来获得预期的结果?
What should I put instead of "int $0x80" to receive expected result?
推荐答案
对于amd64,您需要使用"syscall"-并使用不同的寄存器-而不是"int 0x80":
For amd64, you need to use "syscall" - and use different registers - instead of "int 0x80":
http://cs.lmu.edu/~ray/notes/linuxsyscalls/
http://blog.rchapman .org/post/36801038863/linux-system-call-table-for-x86-64
http://crypto.stanford.edu/~blynn/rop/
这是一个很好的例子:
如何通过内联汇编(x86/amd64 linux)中的sysenter调用系统调用?
#include <unistd.h>
int main(void)
{
const char hello[] = "Hello World!\n";
const size_t hello_size = sizeof(hello);
ssize_t ret;
asm volatile
(
"movl $1, %%eax\n\t"
"movl $1, %%edi\n\t"
"movq %1, %%rsi\n\t"
"movl %2, %%edx\n\t"
"syscall"
: "=a"(ret)
: "g"(hello), "g"(hello_size)
: "%rdi", "%rsi", "%rdx", "%rcx", "%r11"
);
return 0;
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