linux-kernel - Re: [PATCH 4/5 v3] ftrace/x86_32: Clean up ftrace_regs

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Message-ID: <20170316152431.05316146@gandalf.local.home>
Date:   Thu, 16 Mar 2017 15:24:31 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 4/5 v3] ftrace/x86_32: Clean up ftrace_regs_caller

On Thu, 16 Mar 2017 15:19:32 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> 
> The thing is we don't return, we jump to the location that may be
> modified to run the function graph tracer.

That said, maybe the below is better?

	/* restore flags */
	pushl	14*4(%esp)
	popf

	/* Move return ip back to its original location */
	movl	12*4(%esp), %eax
	movl	%eax, 14*4(%esp)

	popl	%ebx
	popl	%ecx
	popl	%edx
	popl	%esi
	popl	%edi
	popl	%ebp
	popl	%eax
	popl	%ds
	popl	%es
	popl	%fs
	popl	%gs

	/* use lea to not affect flags */
	lea	(3*4)%esp, %esp			/* Skip orig_ax, ip and flags */

	jmp	.Lftrace_ret

-- Steve