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

Thomas Gleixner
2014-10-27T20:52:16Z

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