Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751486AbbDFHDi (ORCPT ); Mon, 6 Apr 2015 03:03:38 -0400 Received: from mail-wg0-f47.google.com ([74.125.82.47]:34443 "EHLO mail-wg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750933AbbDFHDe (ORCPT ); Mon, 6 Apr 2015 03:03:34 -0400 Date: Mon, 6 Apr 2015 09:03:29 +0200 From: Ingo Molnar To: Brian Gerst Cc: "H. Peter Anvin" , Andy Lutomirski , Denys Vlasenko , Linus Torvalds , Borislav Petkov , the arch/x86 maintainers , Linux Kernel Mailing List Subject: Re: [PATCH] x86/signal: Remove pax argument from restore_sigcontext Message-ID: <20150406070329.GA30088@gmail.com> References: <1428152303-17154-1-git-send-email-brgerst@gmail.com> <20150404141434.GC22756@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1688 Lines: 42 * Brian Gerst wrote: > > I'm wondering what the original reason for adding the extra > > handling of regs->ax was. Maybe something changed regs->ax - but I > > cannot find such code path anymore. > > > > It would be nice to try to do a bit of Git archeology to figure > > out the origins of this complication - maybe it's something subtle > > - or it's something that has changed meanwhile. > > It goes all the way back to 2.1.106pre1, when restore_sigcontext() > was changed to return an error code instead of EAX directly. > > https://git.kernel.org/cgit/linux/kernel/git/history/history.git/diff/arch/i386/kernel/signal.c?id=9a8f8b7ca3f319bd668298d447bdf32730e51174 Indeed: restore_sigcontext() used to return eax as a return value, without copying it into regs->ax. Then in 2007 sigaltstack syscall support was added, where the return value of restore_sigcontext() was changed to carry the memory-copying failure code. But instead of putting 'ax' into regs->ax, it was carried in via a pointer and then returned, where the generic syscall return code copied it to regs->ax. So there was never any deeper reason for this suboptimal pattern, it was simply never noticed after being introduced. (Btw., the regs->ax we return will be copied back to regs->ax after the syscall straight away once again - but I guess this cannot be helped.) I've added this information to the changelog. Thanks, Ingo -- 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/