From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/10445 Path: news.gmane.org!.POSTED!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: incompatibility between libtheora/mmx and musl ? Date: Wed, 14 Sep 2016 10:39:42 -0400 Message-ID: <20160914143941.GA15995@brightrain.aerifal.cx> References: <20160913180649.GN16436@example.net> <20160913204304.GY15995@brightrain.aerifal.cx> <20160914103253.GO16436@example.net> <20160914112400.GS1280@port70.net> <20160914140450.GQ16436@example.net> <20160914142842.GZ15995@brightrain.aerifal.cx> <20160914173138.034eab55@vostro> 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 1473864006 7087 195.159.176.226 (14 Sep 2016 14:40:06 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 14 Sep 2016 14:40:06 +0000 (UTC) User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-10458-gllmg-musl=m.gmane.org@lists.openwall.com Wed Sep 14 16:39:59 2016 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 1bkBLy-000170-CF for gllmg-musl@m.gmane.org; Wed, 14 Sep 2016 16:39:58 +0200 Original-Received: (qmail 23734 invoked by uid 550); 14 Sep 2016 14:39:58 -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 23713 invoked from network); 14 Sep 2016 14:39:57 -0000 Content-Disposition: inline In-Reply-To: <20160914173138.034eab55@vostro> Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:10445 Archived-At: On Wed, Sep 14, 2016 at 05:31:37PM +0300, Timo Teras wrote: > On Wed, 14 Sep 2016 10:28:42 -0400 > Rich Felker wrote: > > > > > there can be some call abi issue (register clobbering, > > > > stack alignment,..) because of the asm, but that's hard > > > > to check. > > > > > > Is musl in any way special compared to glibc/uclibc in its register > > > usage? > > > > Not in principle; this is mandated by the ABI. But it's possible that > > their violation of ABI contracts is visible with some implementations > > but not others. For example if they're calling malloc from code that's > > using asm it's possible that they assume the floating point registers > > (or mmx state) are call-saved rather than call-clobbered. This is an > > invalid assumption that might happen to actively break on musl but not > > glibc. IIRC you need some special instructions to switch between x87 > > and (original) mmx usage; perhaps they're missing this somewhere. > > Also, since it's Alpine (mentioned in first there with the bug report), > we compile everything PIE. So on x86 ebx is reserved and should not be > clobbered. ebx is always a call-saved register in the x86 ABI, though. The difference is that, if they make any cross-library calls that may go through the PLT, ebx must point to the caller's GOT at the time of the call. But this difference only applies in the main-program (for static-linked libtheora, for instance); with dynamic linking the code is already required to be PIC and thus already has to be taking this into account. Rich