linux-kernel - Re: Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and

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Message-ID: <20131204085953.GC31778@gmail.com>
Date:	Wed, 4 Dec 2013 09:59:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Regression due to 0c44c2d0f459 x86: Use asm goto to implement
 better modify_and_test() functions


* H. Peter Anvin <hpa@...or.com> wrote:

> Hi guys,
> 
> 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test()
> functions
> 
> causes a regression, because it incorrectly changed the constraints of
> bitops.
> 
> Specifically, the GEN_BINARY_RMWcc() hardcodes a constraint as "er", but
> it needs to be "Ir" for the bitops themselves.  "I" is correct (as
> opposed to "J" even on 64 bits, because we only generate the 64-bit
> version when we have a register operand.
> 
> Unfortunately there isn't a way we can get gcc+gas to generate a version
> with an offset pointer.

Does the regression manifest itself in any actual breakage - if yes, 
how does it look like? (People experiencing similar symptoms will be 
helped by seeing a fix matching their problems.)

Thanks,

	ngo
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