linux-kernel - Re: inline asm semantics: output constraint width smaller than input

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Message-ID: <497A0ABD.2090408@zytor.com>
Date:	Fri, 23 Jan 2009 10:21:49 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Török Edwin <edwintorok@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: inline asm semantics: output constraint width smaller than	input

Ingo Molnar wrote:
> 
>> Hi,
>>
>> I am trying to build the kernel with LLVM 2.5 prerelease (using 
>> llvm-gcc-4.2 frontend), however I am running into some inline asm 
>> semantics issues, and after some discussion on LLVM bugzilla I would 
>> like to know if you would be accepting patches for this: 
>> http://llvm.org/bugs/show_bug.cgi?id=3373
>>
>> The problem is when "a" output constraint is used with a variable of 
>> smaller width than the "0" input constraint.
>>

IMO, that's an LLVM bug and should be fixed in LLVM while it is in 
prerelease.  That particular constraint is a serious one, and will haunt 
us for many years if we allow ourselves to go down the path of having to 
fix that every time it crops up.

	-hpa
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