From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7694 Path: news.gmane.org!not-for-mail From: Felix Janda Newsgroups: gmane.linux.lib.musl.general Subject: Re: ppc soft-float regression Date: Tue, 19 May 2015 00:07:31 +0200 Message-ID: <20150518220731.GA31132@euler> References: <20150517080321.GL16123@waldemar-brodkorb.de> <20150517100218.GA2754@euler> <20150517163723.GP17573@brightrain.aerifal.cx> <20150517175021.GA2171@euler> <20150517181556.GA23050@euler> <20150517195622.GA4761@euler> <20150518183929.GA6370@euler> <20150518201043.GX17573@brightrain.aerifal.cx> <20150518201422.GY17573@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1431986880 7556 80.91.229.3 (18 May 2015 22:08:00 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 18 May 2015 22:08:00 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7706-gllmg-musl=m.gmane.org@lists.openwall.com Tue May 19 00:08:00 2015 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1YuTCZ-0007Gi-2Q for gllmg-musl@m.gmane.org; Tue, 19 May 2015 00:07:59 +0200 Original-Received: (qmail 8177 invoked by uid 550); 18 May 2015 22:07:57 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 8159 invoked from network); 18 May 2015 22:07:57 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline In-Reply-To: <20150518201422.GY17573@brightrain.aerifal.cx> User-Agent: Mutt/1.5.23 (2014-03-12) Xref: news.gmane.org gmane.linux.lib.musl.general:7694 Archived-At: Rich Felker wrote: > On Mon, May 18, 2015 at 04:10:43PM -0400, Rich Felker wrote: > > OK I've looked at this and I understand what's happening. PowerPC does > > not have a separate relocation type for GOT entries; instead it uses > > the same relocation type used for address constants global data. These > > do not get re-processed after the main program and libraries are > > added, because unlike GOT slots, they have addends, and if the addend > > is inline (using REL rather than RELA) then it's already been > > clobbered by the early relocation phase and can't easily be recovered. > > > > I see three possible solutions: > > > > 1. Treat R_PPC_ADDR32 as a GOT relocation instead of a regular > > symbolic relocation in data. This would suppress the addend (giving > > wrong address) if inline addends (REL) were used, but in practice > > powerpc aways uses RELA. I consider this a hack, and perhaps risky, > > since in principle someone could make powerpc binaries with REL. > > > > 2. Re-process not just GOT type relocs, but also any RELA > > (non-inline-addend) relocs again on the second pass. This would > > work as long as powerpc only uses RELA, and if REL is ever used, > > the worst that would happen is the current bug (losing environ, > > etc.) rather than silently wrong relocations in global data. This > > approach is not a hack, but I consider it something of an > > incomplete fix. > > > > 3. Re-process all symbolic relocations. For REL-type (inline addend), > > we have to recover the original addend, which can be done by > > calling find_sym again, but using ldso instead of the current > > library chain head as the context to search for the symbol in, then > > subtracting the resulting address to get back the original addend. > > > > I like the third solution best, even though it incurs a small code > > size cost and a performance cost for archs using REL, because it's > > completely robust against any weird ways some archs might end up using > > relocations. The expected number of such relocations is tiny anyway; > > on my i386 builds it's 14. > > > > If option 3 proves to be difficult or costly, however, we could > > consider option 2 as a temporary measure to get powerpc working. It > > wouldn't even need to be reverted, because option 3 includes/subsumes > > the work that would be done for option 2. > > Attached is a patch to implement option 2. I'll probably commit it > soon anyway but here is it in case you want to test sooner. I verified > it fixes the test program on powerpc for me. Thanks for the quick fix! The new commit fixes also the other segfaults I've seen. Felix