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

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Date:	Mon, 27 Oct 2014 17:13:03 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Richard Guy Briggs <rgb@...hat.com>, linux-kernel@...r.kernel.org,
	przanoni@...il.com, mingo@...nel.org, hpa@...ux.intel.com,
	hpa@...or.com, linux-tip-commits@...r.kernel.org,
	linux-audit@...hat.com
Subject: Re: [PATCH] i386/audit: stop scribbling on the stack frame

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


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