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Date: Wed, 31 May 2017 06:17:16 -0700
From: Kees Cook <>
To: Peter Zijlstra <>
Cc: LKML <>, Christoph Hellwig <>, 
	"Eric W. Biederman" <>, Andrew Morton <>, 
	Josh Poimboeuf <>, PaX Team <>, Jann Horn <>, 
	Eric Biggers <>, Elena Reshetova <>, 
	Hans Liljestrand <>, David Windsor <>, 
	Greg KH <>, Ingo Molnar <>, 
	Alexey Dobriyan <>, "Serge E. Hallyn" <>,, 
	Davidlohr Bueso <>, Manfred Spraul <>, 
	"" <>, James Bottomley <>, 
	"" <>, Ingo Molnar <>, Arnd Bergmann <>, 
	"David S. Miller" <>, Rik van Riel <>, 
	linux-arch <>, 
	"" <>
Subject: Re: [PATCH v5 2/3] x86/asm: Add suffix macro for GEN_*_RMWcc()

On Wed, May 31, 2017 at 4:13 AM, Peter Zijlstra <> wrote:
> On Tue, May 30, 2017 at 02:39:51PM -0700, Kees Cook wrote:
>> The coming x86 refcount protection needs to be able to add trailing
>> instructions to the GEN_*_RMWcc() operations. This extracts the
>> difference between the goto/non-goto cases so the helper macros
>> can be defined outside the #ifdef cases. Additionally adds argument
>> naming to the resulting asm for referencing from suffixed
>> instructions, and adds clobbers for "cc", and "cx" to let suffixes
>> use _ASM_CX, and retain any set flags.
> Another option is to simply require __GCC_ASM_FLAG_OUTPUT__ for the fast
> refcount stuff. That would result in simpler and more readable code.

What versions of GCC support that?


Kees Cook
Pixel Security

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