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

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Message-ID: <468AD767.10700@goop.org>
Date:	Tue, 03 Jul 2007 16:10:31 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Chuck Ebbert <cebbert@...hat.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	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 was told in absolute terms that any use of &&label other than to pass 
it to goto was not supported, and would not be supported.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29305

Seems that passing to an asm() falls into the same class of problem I 
had.  I think the underlying problem is that if the code containing the 
label is in an inlined function or unrolled loop, the reference can't be 
resolved properly anyway.

    J
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