From owner-freebsd-hackers@FreeBSD.ORG Mon Nov 2 22:14:29 2009 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 41795106566B; Mon, 2 Nov 2009 22:14:29 +0000 (UTC) (envelope-from a_best01@uni-muenster.de) Received: from zivm-exrelay1.uni-muenster.de (ZIVM-EXRELAY1.UNI-MUENSTER.DE [128.176.192.14]) by mx1.freebsd.org (Postfix) with ESMTP id 9A4FC8FC17; Mon, 2 Nov 2009 22:14:28 +0000 (UTC) X-IronPort-AV: E=Sophos;i="4.44,670,1249250400"; d="scan'208";a="287182124" Received: from zivmaildisp1.uni-muenster.de (HELO ZIVMAILUSER04.UNI-MUENSTER.DE) ([128.176.188.85]) by zivm-relay1.uni-muenster.de with ESMTP; 02 Nov 2009 23:14:27 +0100 Received: by ZIVMAILUSER04.UNI-MUENSTER.DE (Postfix, from userid 149459) id 82C7A1B07BE; Mon, 2 Nov 2009 23:14:27 +0100 (CET) Date: Mon, 02 Nov 2009 23:14:27 +0100 (CET) From: Alexander Best Sender: Organization: Westfaelische Wilhelms-Universitaet Muenster To: John Baldwin , Alexander Best Message-ID: In-Reply-To: <200911021702.07938.jhb@freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: freebsd-hackers@freebsd.org, Alan Cox Subject: Re: mmap(2) with MAP_ANON honouring offset although it shouldn't X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 Nov 2009 22:14:29 -0000 John Baldwin schrieb am 2009-11-02: > On Monday 02 November 2009 4:05:56 pm Alexander Best wrote: > > John Baldwin schrieb am 2009-11-02: > > > On Friday 30 October 2009 10:38:24 pm Alexander Best wrote: > > > > John Baldwin schrieb am 2009-10-21: > > > > > On Wednesday 21 October 2009 11:51:04 am Alexander Best > > > > > wrote: > > > > > > although the mmap(2) manual states in section MAP_ANON: > > > > > > "The offset argument is ignored." > > > > > > this doesn't seem to be true. running > > > > > > printf("%p\n", mmap((void*)0x1000, 0x1000, PROT_NONE, > > > > > > MAP_ANON, > > > > > > -1, > > > > > > 0x12345678)); > > > > > > and > > > > > > printf("%p\n", mmap((void*)0x1000, 0x1000, PROT_NONE, > > > > > > MAP_ANON, > > > > > > -1, > > > > > > 0)); > > > > > > produces different outputs. i've attached a patch to solve > > > > > > the > > > > > > problem. the > > > > > > patch is similar to the one proposed in this PR, but should > > > > > > apply > > > > > > cleanly to > > > > > > CURRENT: > > > > > > http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/71258 > > > > > A simpler patch would be to simply set pos = 0 below the > > > > > MAP_STACK > > > > > line if > > > > > MAP_ANON is set. > > > > how about the following patch. problem seems to be that pos = 0 > > > > needs to be > > > > set before pageoff is being calculated. > > > I think that that patch is fine, but will defer to alc@. I think > > > he > > > argued > > > that any non-zero offset passed to MAP_ANON should fail with > > > EINVAL. > > thanks. if that's what the POSIX standard requests that's ok. > > however in that > > case we need to change the mmap(2) manual, because right now it > > says in > > section MAP_ANON: > > "The offset argument is ignored." > > which should be changed to something like: > > "The offset argument must be zero." > > also if the behaviour of MAP_ANON changes this also changes the > > semantics of > > MAP_STACK since it implies MAP_ANON. so we need to decide if > > MAP_STACK should > > silently reset any offset value to zero or like MAP_ANON should > > fail if offset > > isn't zero in which case the MAP_STACK section of the mmap(2) > > manual needs to > > be changed to someting like: > > "MAP_STACK implies MAP_ANON, and requires offset to be zero." > Right now MAP_STACK sets pos to 0 in the current code, and I don't > expect we > would remove that if we decide to reject non-zero offsets for > MAP_ANON. I'd > probably rather err on the side of leniency and just ignore the > offset rather > than rejecting non-zero, but I'm a bit burned from the last round of > mmap() > API changes. :) hmmm...i think this will require quite a few changes. if i remember correctly MAP_STACK at some point does: flags =| MAP_ANON; so if we decide MAP_ANON and MAP_STACK should behave differently this will require some checks to distinguish between both flags further down in the code. let's see what alc@ thinks about this one then. API changes are a nasty nasty business. ;)