Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753866AbbHMWCe (ORCPT ); Thu, 13 Aug 2015 18:02:34 -0400 Received: from smtp44.i.mail.ru ([94.100.177.104]:39846 "EHLO smtp44.i.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753216AbbHMWCd (ORCPT ); Thu, 13 Aug 2015 18:02:33 -0400 Subject: Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu To: Linus Torvalds , Raymond Jennings References: <55CA90B4.2010205@list.ru> <55CCD921.4040301@list.ru> <20150813200823.GS2059@uranus> <55CD0F29.4070604@gmail.com> Cc: Cyrill Gorcunov , Andy Lutomirski , Pavel Emelyanov , Linux kernel From: Stas Sergeev Message-ID: <55CD13F3.1070904@list.ru> Date: Fri, 14 Aug 2015 01:02:27 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Mras: Ok Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1311 Lines: 26 14.08.2015 00:46, Linus Torvalds пишет: > On Thu, Aug 13, 2015 at 2:42 PM, Raymond Jennings wrote: >> I am curious about what's supposed to happen normally on signal delivery. >> >> Is SS a register that's supposed to be preserved like EIP/RIP and CS when a >> signal is delivered? > What exactly does "supposed" mean? > > On x86-64, we traditionally haven't touched SS, because it doesn't > really matter in 64-bit long mode. And apparently dosemu depended on > that behavior. > > So clearly, we're not "supposed" to save/restore it. Because reality > matters a hell of a lot more than any theoretical arguments. Unless you introduce some clever flag to explicitly request its restoring. There is another problem as well which is that gcc assumes FS base to point to TLS at function prolog. Since FS is not restored too, the only suggestion I get is to write a sighandlers in asm... I wonder if someone really should write a sighandler in asm to restore FS base manually with a syscall. So I think the reality is asking for a new flag. :) -- 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/