linux-kernel - Re: [PATCH 5/6] x86: Remove useless unwinder backlink from irq regs saving

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Message-ID: <20110704132158.GA5551@somewhere>
Date:	Mon, 4 Jul 2011 15:22:23 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 5/6] x86: Remove useless unwinder backlink from irq regs
 saving

On Mon, Jul 04, 2011 at 08:29:08AM +0100, Jan Beulich wrote:
> >>> On 02.07.11 at 18:29, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > The unwinder backlink in interrupt entry is very useless.
> > It's actually not part of the stack frame chain and thus is
> > never used.
> 
> I very much doubt this - see dump_trace()'s comment in its IRQ-stack
> related code portion (and the corresponding use of irq_stack_end[-1]).
> 
> Jan

Good point. I misunderstood that.

But then I believe I accidentally fixed it back in
"x86: Don't use frame pointer to save old stack on irq entry" by
pushing %rsi instead in the new stack. It contains the backlink to
the old stack.

If we keep the macro as-is, I'll add a comment to explain further
what is involved there.
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