x86_64 system call entry points

[Martin Bisson]

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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