Date: Wed, 31 May 2017 09:09:16 -0700 From: Kees Cook <keescook@...omium.org> To: Peter Zijlstra <peterz@...radead.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 7:03 AM, Peter Zijlstra <peterz@...radead.org> wrote: > 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+ Given how many folks are still using 4.9 (and lower, see the thread with Arnd), I'd like to just keep this as I have it. It's not much less readable, IMO (It was already pretty complex). I cleaned it up a little before making it more ugly, so I think on sum, it's only a little more weird. I think that's better than making this compiler-specific or copy/pasting. -Kees  https://lkml.org/lkml/2017/4/25/66 -- Kees Cook Pixel Security
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