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Date: Wed, 31 May 2017 16:03:18 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Kees Cook <keescook@...omium.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	PaX Team <pageexec@...email.hu>, Jann Horn <jannh@...gle.com>,
	Eric Biggers <ebiggers3@...il.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	Hans Liljestrand <ishkamiel@...il.com>,
	David Windsor <dwindsor@...il.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Serge E. Hallyn" <serge@...lyn.com>, arozansk@...hat.com,
	Davidlohr Bueso <dave@...olabs.net>,
	Manfred Spraul <manfred@...orfullife.com>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	"x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	"David S. Miller" <davem@...emloft.net>,
	Rik van Riel <riel@...hat.com>,
	linux-arch <linux-arch@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v5 2/3] x86/asm: Add suffix macro for GEN_*_RMWcc()

On Wed, May 31, 2017 at 06:17:16AM -0700, Kees Cook wrote:
> On Wed, May 31, 2017 at 4:13 AM, Peter Zijlstra <peterz@...radead.org> 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?

IIRC 6+

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