From owner-freebsd-hackers@FreeBSD.ORG Mon Nov 2 22:02:14 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 E28681065679 for ; Mon, 2 Nov 2009 22:02:13 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id B5F6F8FC08 for ; Mon, 2 Nov 2009 22:02:13 +0000 (UTC) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id 5D69146B03; Mon, 2 Nov 2009 17:02:13 -0500 (EST) Received: from jhbbsd.hudson-trading.com (unknown [209.249.190.8]) by bigwig.baldwin.cx (Postfix) with ESMTPA id 9D5C98A01D; Mon, 2 Nov 2009 17:02:12 -0500 (EST) From: John Baldwin To: Alexander Best Date: Mon, 2 Nov 2009 17:02:07 -0500 User-Agent: KMail/1.9.7 References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200911021702.07938.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (bigwig.baldwin.cx); Mon, 02 Nov 2009 17:02:12 -0500 (EST) X-Virus-Scanned: clamav-milter 0.95.1 at bigwig.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-2.5 required=4.2 tests=AWL,BAYES_00,RDNS_NONE autolearn=no version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on bigwig.baldwin.cx 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 22:02:14 -0000 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. :) -- John Baldwin