linux-kernel - Re: [patch 1/2] i386: add CFI macros for stack manipulation

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Date:	Fri, 28 Jul 2006 15:40:36 -0400
From:	Chuck Ebbert <76306.1226@...puserve.com>
To:	Andi Kleen <ak@...e.de>
Cc:	Linus Torvalds <torvalds@...l.org>, Andrew Morton <akpm@...l.org>,
	Jan Beulich <jbeulich@...ell.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/2] i386: add CFI macros for stack manipulation

In-Reply-To: <200607282036.45608.ak@...e.de>

On Fri, 28 Jul 2006 20:36:45 +0200, Andi Kleen wrote:
> 
> On Friday 28 July 2006 19:50, Chuck Ebbert wrote:
> > Add macros to dwarf2.h to simplify pushing and popping stack
> > variables.
> 
> I feared someone would do that patch. I've thought about it myself.
> 
> However it's not a good idea. I've already had complaints that some code in 
> x86-64 is too hard to read/debug because it uses too many macros. I think 
> it's better  if the core core still uses "real" instructions and keep the 
> CFI_* stuff as annotation that most people can just ignore.

I did this because it should prevent:

| Date: Thu, 27 Jul 2006 07:45:35 +0200
| From: Markus Armbruster <armbru@...hat.com>
| Subject: [PATCH] Fix trivial unwind info bug
| To: linux-kernel@...r.kernel.org
| Message-ID: <874px31tz4.fsf@...e.pond.sub.org>
| Content-Type: text/plain; charset=us-ascii
| 
| CFA needs to be adjusted upwards for push, and downwards for pop.
| arch/i386/kernel/entry.S gets it wrong in one place.
| 
| Signed-off-by: Markus Armbruster <armbru@...hat.com>
| 
| 
| diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
| index d9a260f..37a7d2e 100644
| --- a/arch/i386/kernel/entry.S
| +++ b/arch/i386/kernel/entry.S
| @@ -204,7 +204,7 @@ #define RING0_PTREGS_FRAME \
|  ENTRY(ret_from_fork)
|         CFI_STARTPROC
|         pushl %eax
| -       CFI_ADJUST_CFA_OFFSET -4
| +       CFI_ADJUST_CFA_OFFSET 4
|         call schedule_tail
|         GET_THREAD_INFO(%ebp)
|         popl %eax

Otherwise I was just going to indent the annotations an additional
tabstop to move them out of the way.  (They really annoy me.)

-- 
Chuck

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