System call not working in inline assembler, what's the problem?

Question

linux

int main(void)
{
  char *path = "tmp/path";
  asm(
        "movl $39, %%eax\n\t"
        "movl %0, %%ecx\n\t"
        "movl $0x1ff, %%ebx\n\t"
        "int $0x80\n\t" : "r"(path) : "%eax" : "%ebx" : "%ecx"
    );
    return 0;
}

Answer 1

Let's start with what doesn't "doesn't work" and doesn't even compile. Because
1. you have the only in-parameter, you need to specify it after the second colon
2. you have 3 clobbered registers, you need to specify them with a comma after the third colon, i.e.

int main(void)
{
        char *path = "tmp/path";
        asm (
             "movl $39, %%eax\n\t"
             "movl %0, %%ecx\n\t"
             "movl $0x1ff, %%ebx\n\t"
             "int $0x80\n\t"
             : : "r"(path)
             : "%eax", "%ebx", "%ecx"
            );
        return 0;
}

3. it is necessary to collect, judging by the code, under 32 bits, i.e. gcc -m32
And after it is compiled, it doesn't work, because
4. you have the order of the arguments mixed up, the path should go to ebx, the attributes of the created directory to ecx

Answer 2

Please read the official documentation on inline assembler from gnu and many things will fall into place, here is an example of calling syscall exit

int main(void)
{
__asm__("movl $1,%eax\n\t"         
"xorl %ebx,%ebx\n\t"    
"int  $0x80\n\t");
return 0;
}