linux-kernel - Re: [RFC,v2] x86_64: save

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Date:	Tue, 18 Nov 2008 16:08:13 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Jan Beulich <jbeulich@...ell.com>,
	heukelum@...tmail.fm, Thomas Gleixner <tglx@...utronix.de>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	Glauber Costa <gcosta@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [RFC,v2] x86_64: save_args out of line

H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
>>
>> Not really.  At the moment we have two parallel assembly languages 
>> which say different things about the same instructions.  In practice, 
>> almost nobody understands the cfi parts, so they just get ignored 
>> while the x86 instructions change around them, leaving them either 
>> stale or missing.
>>
>> If we had a sensible macro layer which emits both instructions and 
>> cfi annotations, it at least means that people who write plain x86 
>> instructions will simply get no annotations, and people who bother to 
>> learn the (clearly and fully documented) macros will get the best of 
>> both.
>>
>
> I think that it would be nice to have macros for the most commonly 
> annotatable instructions, e.g. push, and stack pointer movement.  Just 
> compactifying the code should improve readability, if perhaps not 
> writability.

Yes.  Something that obviously relates to both the instruction and the 
semantic intent of the annotation: add_sp, sub_sp, save_reg, etc.  And 
at least that will eliminate the differently-signed(!) constant for 
stack movement.

    J
>
>     -hpa

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