Re: [PATCH 3/5] x86/asm/entry/32: Shorten __audit_syscall_entry args preparation

Ingo Molnar
2015-06-10T06:21:25Z

* Denys Vlasenko <dvlasenk@redhat.com> wrote:

> We use three MOVs to swap edx and ecx. We can use one XCHG instead.
>
> Expand the comments. It's difficult to keep track which arg# every register
> corresponds to, so spell it out.

> + /*
> + * At this point, registers hold syscall args in 32-bit ABI:
> + * eax is syscall#, args are in ebx,ecx,edx,esi,edi,ebp.
> + * Shuffle them to match what __audit_syscall_entry() wants.
> + */
> + movl %esi, %r8d /* arg5 (r8): 4th syscall arg */
> + xchg %ecx, %edx /* arg4 (rcx): 3rd syscall arg (edx) */
> + /* arg3 (rdx): 2nd syscall arg (ecx) */
> + movl %ebx, %esi /* arg2 (rsi): 1st syscall arg */
> + movl %eax, %edi /* arg1 (rdi): syscall number */
> call __audit_syscall_entry

So while we are at it I improved this a bit more, to:

/*
* At this point, registers hold syscall args in 32-bit syscall ABI:
* eax is syscall#, args are in ebx,ecx,edx,esi,edi,ebp.
*
* We want to pass them to __audit_syscall_entry(), which is a 64-bit
* C function with 5 parameters, so shuffle them to match what
* __audit_syscall_entry() expects: rdi,rsi,rdx,rcx,r8.
*/
movl %esi, %r8d /* arg5 (r8 ) <= 4th syscall arg (esi) */
xchg %ecx, %edx /* arg4 (rcx) <= 3rd syscall arg (edx) */
/* arg3 (rdx) <= 2nd syscall arg (ecx) */
movl %ebx, %esi /* arg2 (rsi) <= 1st syscall arg (ebx) */
movl %eax, %edi /* arg1 (rdi) <= syscall number (eax) */
call __audit_syscall_entry

Btw., syscall auditing is not auditing syscall arguments #5 and #6?

Thanks,

Ingo