From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752541Ab2H1S2b (ORCPT ); Tue, 28 Aug 2012 14:28:31 -0400 Received: from cantor2.suse.de ([195.135.220.15]:36367 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751760Ab2H1S21 (ORCPT ); Tue, 28 Aug 2012 14:28:27 -0400 Date: Tue, 28 Aug 2012 11:28:11 -0700 (PDT) From: Jiri Kosina To: Arnd Bergmann Cc: Will Deacon , Catalin Marinas , "linux-arch@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , x86@kernel.org, Martin Schwidefsky , Heiko Carstens , "David S. Miller" , Andi Kleen , "James E.J. Bottomley" , Ralf Baechle , Benjamin Herrenschmidt , Paul Mackerras Subject: Re: PER_LINUX32, Was: [PATCH v2 21/31] arm64: 32-bit (compat) applications support In-Reply-To: <201208230646.31276.arnd@arndb.de> Message-ID: References: <1344966752-16102-1-git-send-email-catalin.marinas@arm.com> <201208151434.05145.arnd@arndb.de> <20120816102808.GH31784@mudshark.cambridge.arm.com> <201208230646.31276.arnd@arndb.de> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 23 Aug 2012, Arnd Bergmann wrote: > > > > +asmlinkage int compat_sys_personality(compat_ulong_t personality) > > > > +{ > > > > + int ret; > > > > + > > > > + if (personality(current->personality) == PER_LINUX32 && > > > > + personality == PER_LINUX) > > > > + personality = PER_LINUX32; > > > > + ret = sys_personality(personality); > > > > + if (ret == PER_LINUX32) > > > > + ret = PER_LINUX; > > > > + return ret; > > > > +} > > > > > > Where did you get this from? > > > > > > You should not need compat_sys_personality, just call the native function. > > > > Hmm, but in that case an aarch32 application doing a personality(PER_LINUX) > > syscall will start seeing the wrong uname. > > Coming back at this topic, I noticed another issue. Jiri Kosina > has recently posted patches to fix this function in the other architectures Yeah, there were quite a few broken ones, some of them since the beginning of time. > in order to mask out the other personality bits, which is a correct fix, > but the above function is odd for other reasons. > > * On MIPS, it is used only for compat tasks, like you have it above. > * On PA-RISC, it is used for native 32 bit tasks and for compat 32 bit tasks, > but not for native 64 bit ones. > * On IA64, it was used for compat tasks (support for which has since > been removed from the kernel), plus all 32 bit tasks would start with > PER_LINUX32. > * On PowerPC, Sparc and s390, it is used for native 64 bit tasks and for > compat 32 bit tasks, but not for native 32 bit ones. > * On Tile, it was never used. > * On x86_64, it used to be defined (copied from ia64) but not used > throughout the git history. > > The semantics of the function are also interesting: The intention seems > to be that to a compat task, PER_LINUX32 would appear as PER_LINUX. > The effect is that any process can set PER_LINUX32 but it can never > be unset except by a 64 bit MIPS or PA-RISC task. > > Since x86_64 does not implement this behavior at all, I suspect that > there are now lots of things depending on not having it, while all > the other architectures might also have some (even predating the > x86_64 port) use cases that depend on depend on not being able to > observe PER_LINUX32 in 32 bit compat tasks. > > I think we should try to agree on how this is all supposed to work > and use common code, either put the ppc/sparc/s390 version into > sys_personality, or remove all of them and just do what x86 and tile > do, using the regular sys_personality for all tasks. How about rather introducing common compat_sys_personality() and switching the archs that are using it to it? Unifying the behavior (PER_LINUX / PER_LINUX32 masquerading) should be painless. Thanks, -- Jiri Kosina SUSE Labs