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

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Message-ID: <alpine.DEB.2.11.1410272150000.5308@nanos>
Date:	Mon, 27 Oct 2014 21:52:16 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Richard Guy Briggs <rgb@...hat.com>
cc:	linux-kernel@...r.kernel.org, eparis@...hat.com,
	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 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?

Thanks,

	tglx
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