From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.1 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 Received: from second.openwall.net (second.openwall.net [193.110.157.125]) by inbox.vuxu.org (Postfix) with SMTP id 703FB2D8C9 for ; Thu, 29 Aug 2024 21:04:02 +0200 (CEST) Received: (qmail 1923 invoked by uid 550); 29 Aug 2024 19:03:57 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 1876 invoked from network); 29 Aug 2024 19:03:56 -0000 Date: Thu, 29 Aug 2024 15:03:48 -0400 From: Rich Felker To: alice Cc: musl@lists.openwall.com Message-ID: <20240829190348.GL10433@brightrain.aerifal.cx> References: <20240829125727.GK10433@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] [PATCH] fix MINSIGSTKSZ and SIGSTKSZ for powerpc64 On Thu, Aug 29, 2024 at 06:00:52PM +0200, alice wrote: > On Thu Aug 29, 2024 at 2:57 PM CEST, Rich Felker wrote: > > On Thu, Aug 29, 2024 at 05:38:42AM +0200, psykose wrote: > > > since kernel commit 2f82ec19757f58549467db568c56e7dfff8af283 > > > (https://github.com/torvalds/linux/commit/2f82ec19757f58549467db568c56e7dfff8af283) > > > the kernel has updated these minimum values. having these small values breaks > > > sysconf(_SC_MINSIGSTKSZ) too; it returns 4224 in musl currently which ends up > > > returning ENOMEM from the syscall made in sigaltstack. > > > > > > raising these to match the kernel fixes sigaltstack use on powerpc64(le). > > > caught by glib's 2.82 testsuite > > > > I don't follow how you're claiming sysconf(_SC_MINSIGSTKSZ) is broken. > > It will just return the kernel-provided value on new kernels that > > insist on having a larger stack. In particular I don't see where the > > value 4224 is supposed to be coming from. If there's something I'm > > missing, please explain. > > sysconf(_SC_MINSIGSTKSZ) returns 4224 on ppc64le (this is as far as i know > expected). I don't have a real system handy to test on, so I'm executing this mentally, and not seeing where 4224 comes from. sysconf(_SC_MINSIGSTKSZ) should return the kernel-provided value from __getauxval(AT_MINSIGSTKSZ) unless it's less than the fixed macro value MINSIGSTKSZ. Since that's 4096, the only way I can see this happening is if the kernel filled in AT_MINSIGSTKSZ as 4224, which would be a kernel bug...? > setting stack.ss_size = 4224 (from that call) and passing it to sigaltstack > returns ENOMEM because it is smaller than 8192 which the kernel enforces. > > ...so the normal way of using sigaltstack with the smallest size (with sysconf or > the macros) is broken. > making the MINSIGSTKSZ match the actual value the kernel enforces fixes it. What the kernel enforces varies by version and possibly also hardware capabilities. Rich