Re: [PATCH] i386/audit: stop scribbling on the stack frame

Eric Paris
2014-10-27T21:13:03Z

On Mon, 2014-10-27 at 21:52 +0100, Thomas Gleixner wrote:
> On Sun, 26 Oct 2014, Richard Guy Briggs wrote:
> > diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> > index b553ed8..344b63f 100644
> > --- a/arch/x86/kernel/entry_32.S
> > +++ b/arch/x86/kernel/entry_32.S
> > @@ -447,15 +447,14 @@ sysenter_exit:
> > sysenter_audit:
> > testl $(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT),TI_flags(%ebp)
> > jnz syscall_trace_entry
> > - addl $4,%esp
> > - CFI_ADJUST_CFA_OFFSET -4
> > - movl %esi,4(%esp) /* 5th arg: 4th syscall arg */
> > - movl %edx,(%esp) /* 4th arg: 3rd syscall arg */
> > - /* %ecx already in %ecx 3rd arg: 2nd syscall arg */
> > - movl %ebx,%edx /* 2nd arg: 1st syscall arg */
> > - /* %eax already in %eax 1st arg: syscall number */
> > + /* movl PT_ECX(%esp), %ecx already set, a1: 3nd arg to audit */
> > + /* movl PT_EAX(%esp), %eax already set, syscall number: 1st arg to audit */
> > + pushl_cfi %esi /* a3: 5th arg */
> > + pushl_cfi %edx /* a2: 4th arg */
> > + movl %ebx, %edx /* ebx/a0: 2nd arg to audit */
> > call __audit_syscall_entry
> > - pushl_cfi %ebx
> > + popl_cfi %ecx /* get that remapped edx off the stack */
> > + popl_cfi %ecx /* get that remapped esi off the stack */
>
> Why use pop instead of simply adjusting esp and CFI by 8?

Certainly seems like a good idea for RGB's perf improvement patch to go
on top of -tip urgent.

-Eric