Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753087AbbDCUkl (ORCPT ); Fri, 3 Apr 2015 16:40:41 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:50701 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753057AbbDCUki (ORCPT ); Fri, 3 Apr 2015 16:40:38 -0400 Date: Fri, 3 Apr 2015 22:42:17 +0200 From: Quentin Casasnovas To: Borislav Petkov Cc: Quentin Casasnovas , X86 ML , LKML , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Oleg Nesterov , Andy Lutomirski Subject: Re: [PATCH] x86/xsave: Robustify and merge macros Message-ID: <20150403204217.GH14902@chrystal.uk.oracle.com> References: <1427980282-25929-1-git-send-email-bp@alien8.de> <20150402155210.GB6703@chrystal.uk.oracle.com> <20150402161259.GE3483@pd.tnic> <20150403140630.GD14902@chrystal.uk.oracle.com> <20150403141426.GE14902@chrystal.uk.oracle.com> <20150403152324.GG3418@pd.tnic> <20150403154055.GF14902@chrystal.uk.oracle.com> <20150403170625.GJ3418@pd.tnic> <20150403173306.GG14902@chrystal.uk.oracle.com> <20150403174824.GL3418@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150403174824.GL3418@pd.tnic> User-Agent: Mutt/1.5.22 (2013-10-16) X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1787 Lines: 51 On Fri, Apr 03, 2015 at 07:48:24PM +0200, Borislav Petkov wrote: > On Fri, Apr 03, 2015 at 07:33:06PM +0200, Quentin Casasnovas wrote: > > > Basically, the idea was: > > > > > > .skip len(repl1) - len(orig), 0x90 > > > .skip len(repl2) - len(repl1), 0x90 > > > > > > BUT!, for some reason I changed it to what's there now and I can't > > > remember why anymore. > > > > I think it would not work in the case where repl1 is smaller or equal than > > orig_insn (i.e. no padding in the first .skip) but orig_insn is strictly > > smaller than repl2 (since we're never comparing repl2 with insn in this > > new-old code). > > orig_insn=4 > repl1=3 > repl2=5 > > .skip 0, 0x90 > .skip 2, 0x90 > > I think that still works, only the padding is larger than it needs to > be. And it is so many bytes larger as len(abs(repl1 - orig_insn)) is. > > In the example above, we'll get two bytes padding while only 1 suffices. > Right. > > Anything wrong with the two different approaches I've suggested in my > > original mail? > > Right now, I want to have a minimal fix for obvious reasons. We can > always improve stuff later when there's more time. > If you're happy with the extra padding in such cases then your second approach looks okay to me. But IMO, even if taking the '.if' directive approach is certainly bigger LOC-wise, it should be much easier to review in a rush than some other .skip trickery. It all depends on your definition of minimal change really, and whether that extra padding is acceptable or not for you :) Quentin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/