Re: x86_64 system call entry points II

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Andi Kleen wrote:

Martin Bisson <[email protected]> writes:
- int $0x80/64 bits: All system calls return -1 (EINTR).  Is there
something wrong in the way I call it:
pid_t getpid64()
{
   pid_t resultvar;

   asm volatile (
   "int $0x80\n\t"
   : "=a" (resultvar)     : "0" (__NR_getpid)
   : "memory");

   return resultvar;
}

I tested it now. Since it ends up as a 32bit syscall you're not actually calling 64bit getpid() - but 32bit mkdir(). That is because 32bit and 64bit
have different syscall numbers. For me it returns -14, which is EFAULT.
Expected for a random argument to mkdir()
It makes a lot of sense...

I think the bottom line for me is simply that I cannot enter system calls any way I want with any kernel, among other things because the kernel expects that we got into the system call using vsyscall stuff and that the correct way to return to user space is also found in the vsyscall page.

Thanks for your input.

Mart
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