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Subjectx86_64 system call entry points
Hi, (first post)

I am trying to trace system calls (entry + exit) on x86_64 architecture,
so I am basically working on arch/x86_64/kernel/entry.S and
arch/x86_64/ia32/ia32entry.S (for 32-bit compatibility). I want to test
that my code works for all possible ways to enter a system call, which
are (to my knowledge) the three following instructions:
- int $0x80
- sysenter
- syscall

So these three ways in, used in a 32 or 64 bits executable, makes 6
possible ways to enter a system call that I need to test. However, I
have problems:

- sysenter/32 bits, executed on a 32 bit machine: I get a segfault on
the sysenter instruction. I use the following code to enter the system
call:
pid_t getpid32()
{
pid_t resultvar;
asm volatile (
"push %%ebp\n\t"
"push %%ecx\n\t"
"push %%edx\n\t"
"mov %%esp,%%ebp\n\t"
"sysenter\n\t"
".space 20,0x90\n\t"
"pop %%edx\n\t"
"pop %%ecx\n\t"
"pop %%ebp\n\t"
: "=a" (resultvar)
: "0" (__NR_getpid)
: "memory");

return resultvar;
}
Is there something wrong in the way I pass the parameters? I know this
instruction can be tricky because of the way it messes different
registers...


- 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;
}

- sysenter/64 bits: I get an illegal instruction. I've read that it's
not implemented on AMD-64 (which is what I have). Is there ANY x86_64
machine on which this instruction is implemented? Does this mean that
the code that handles this case in entry.S has never been run?

- syscall/64 bits: works fine
- int $0x80/32 bits: works fine
- syscall/32 bits: illegal instruction, but I guess that's all right
because of the machine I use.

Can someone help with any of my issues (entering a system call with
sysenter/32 bits, int $0x80/64 bits or sysenter/64 bits)?

Thanks in advance,

Mart

P.S. First post on this list, please reply in private if I did
something wrong so that I won't do it again.
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