linux-kernel - Re: Oops with DCACHE_WORD

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Message-ID: <4FA2F769.40903@zytor.com>
Date:	Thu, 03 May 2012 14:23:53 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Miller <davem@...emloft.net>
CC:	torvalds@...ux-foundation.org, viro@...iv.linux.org.uk,
	npiggin@...il.com, jana@...ut.de, jlbec@...lplan.org,
	linux-kernel@...r.kernel.org
Subject: Re: Oops with DCACHE_WORD_ACCESS and ocfs2, autofs4

On 05/03/2012 11:48 AM, David Miller wrote:
> From: "H. Peter Anvin" <hpa@...or.com>
> Date: Thu, 03 May 2012 11:28:44 -0700
> 
>> +		"lea" __WORDSUFFIX " %2,%1\n\t"
>> +		"and" __WORDSUFFIX " %4,%1\n\t"
>> +		"shl" __WORDSUFFIX " $3,%1\n\t"
>> +		"shr" __WORDSUFFIX " %b1,%0\n\t"
>>
>> Also, for this sequence of instructions using %ecx unconditionally is
>> actually better (avoids REX prefixes on 64 bits.)
> 
> If it doesn't exist already, someone should really add bits to
> binutils so you guys don't have to string paste like this.
> 
> For example a bit a mnenomics that the assembler internally changes
> into the 64-bit or 32-bit variant based upon what bitness it is
> targetting.
> 
> We have these on sparc, for example "ldn" is transformed into "lduw"
> for 32-bit and "ldx" for 64-bit.

I don't think we really need it.  For the vast majority of all
instructions the size is given by the operands, and for the balance we
can generally use %z and/or <asm/asm.h>.  %z would be more useful if
there wasn't for the fact that some now quite old versions of gcc
incorrectly produce "ll" instead of "q".

	-hpa

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