linux-kernel - Re: patch to use more symbolic constants in asm

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Message-Id: <200702211256.43565.ak@suse.de>
Date:	Wed, 21 Feb 2007 12:56:43 +0100
From:	Andi Kleen <ak@...e.de>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...l.org
Subject: Re: patch to use more symbolic constants in asm

On Wednesday 21 February 2007 12:10, Arjan van de Ven wrote:
> From: Arjan van de Ven <arjan@...ux.intel.com>
> Subject: Use symbolic constants in inline assembly
> 
> This patch replaces several of the %0/%1 uses in x86-64 inline assembly
> with symbolic names (this is a new gcc 3.x feature, but that's ok now).
> This tends to, imo, make the inline assembly a lot more readable, and
> for sure it's less error prone in terms of finding which %<number>
> corresponds with which variable.

At least for two arguments i don't really see the value, but ok.

> objdump -d of the vmlinux before and after the patch is the same; also
> boot tested.

You should do i386 too then; one reason I didn't touch bitops 
for example was to keep the code more similar.


>  static inline void set_cr4(unsigned long cr4)
>  {
> -	asm volatile("mov %0,%%cr4" :: "r" (cr4) : "memory");
> +	asm volatile("mov %[cr4],%%cr4" :: [cr4] "r" (cr4) : "memory");

I'm not sure that's really an improvement for example.

-Andi
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