linux-kernel - Re: [PATCH 5/6] ftrace/x86: Add separate function to save regs

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Date:	Wed, 11 Jul 2012 12:22:34 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH 5/6] ftrace/x86: Add separate function to save regs

On Tue, 2012-07-03 at 17:29 +0900, Masami Hiramatsu wrote:


> 
> > +	/* Restore flags */
> > +	pushq EFLAGS(%rsp)
> > +	popfq
> > +
> > +	MCOUNT_RESTORE_FRAME
> 
> Here, if MCOUNT_RESTORE_FRAME has skip too, I think you don't
> need to restore flags before restoring other registers, like
> below;
> 
> 	MCOUNT_RESTORE_FRAME 8
> 	popfq
> 
> And also, this will prevent to modify flags before return by
> addq in MCOUNT_RESTORE_FRAME.

Ah, because the addq will modify flags :-/

Grumble, I guess I should implement this, even though it will make it a
little more complex. I thought it was better to restore flags
explicitly, but that's not the case.

OK, I'll make the update. As MCOUNT_SAVE_FRAME has the skip, I guess
it's not so bad to have restore have it too.

-- Steve

> 
> > +
> > +	jmp ftrace_return
> > +ftrace_restore_flags:
> > +	popfq
> > +	jmp  ftrace_stub
> > +
> > +END(ftrace_regs_caller)
> > +
> 
> Thank you,
> 
> 


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