From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/12300 Path: news.gmane.org!.POSTED!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] Add comments to i386 assembly source Date: Mon, 1 Jan 2018 20:49:15 -0500 Message-ID: <20180102014915.GJ1627@brightrain.aerifal.cx> References: <20171223094545.rmx6xtmucyz5xzap@voyager> <72c68934-4445-c83d-7bbc-004953b2f9e9@bitwagon.com> <20171231154926.GG1627@brightrain.aerifal.cx> <20180101195224.tpkl5g5w66rzwzz3@voyager> <5caf910a-dd98-6836-c70f-6a98cf8a9d22@bitwagon.com> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1514857660 26215 195.159.176.226 (2 Jan 2018 01:47:40 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 2 Jan 2018 01:47:40 +0000 (UTC) User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-12316-gllmg-musl=m.gmane.org@lists.openwall.com Tue Jan 02 02:47:36 2018 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1eWBfq-00061L-Pv for gllmg-musl@m.gmane.org; Tue, 02 Jan 2018 02:47:26 +0100 Original-Received: (qmail 1571 invoked by uid 550); 2 Jan 2018 01:49:28 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 1553 invoked from network); 2 Jan 2018 01:49:27 -0000 Content-Disposition: inline In-Reply-To: <5caf910a-dd98-6836-c70f-6a98cf8a9d22@bitwagon.com> Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:12300 Archived-At: On Mon, Jan 01, 2018 at 02:57:02PM -0800, John Reiser wrote: > There's a bug. clone() is a user-level function that can be used > independently of the musl internal implementation of threads. > Thus when clone() in musl/src/linux/clone.c calls > return __syscall_ret(__clone(func, stack, flags, arg, ptid, tls, ctid)); > then the i386 implementation of __clone has no guarantee about > the value in %gs, and it is a bug to assume that (%gs >> 3) > fits in 8 bits. The ABI is that at function call or any time a signal could be received, %gs must always be a valid segment register value reflecting the current thread's thread pointer. If this is violated, the program has undefined behavior. > The code in musl/src/thread/i386/clone.s wastes up to 12 bytes > when aligning the new stack, by aligning before [pre-]allocating > space for the one argument to the thread function. I suspect the initial value happens to be aligned anyway in which case reserving 16 bytes and aligning to 16 is the same as reserving 4 and aligning to 16. If you think it's not, I don't mind changing if you can do careful testing to make sure it doesn't introduce any bugs. Rich