linux-kernel - Re: [patch 06/10] Immediate Value

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Message-ID: <468ABFEE.3000608@zytor.com>
Date:	Tue, 03 Jul 2007 14:30:22 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Chuck Ebbert <cebbert@...hat.com>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 06/10] Immediate Value - i386 Optimization

Chuck Ebbert wrote:
> On 07/03/2007 04:18 PM, H. Peter Anvin wrote:
>> One could, though, use an indirect jump to achieve, if not as good, at
>> least most of the effect:
>>
>> 	movl	$<patchable>,<reg>
>> 	jmp	*<reg>
>>
> 
> Yeah, but there's this GCC bug:
> 
> 	http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22448
> 
> You can't even dereference labels in an ASM statement.

I wouldn't to that, though, for the existing compiler.   Instead, I
would do:

	void (*func)(void);	/* or what's appropriate */
	asm(<magic movl> : "=rm" (func));
	func();

	-hpa

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