From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7690 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: ppc soft-float regression Date: Mon, 18 May 2015 16:14:23 -0400 Message-ID: <20150518201422.GY17573@brightrain.aerifal.cx> 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> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="f+W+jCU1fRNres8c" X-Trace: ger.gmane.org 1431980078 21150 80.91.229.3 (18 May 2015 20:14:38 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 18 May 2015 20:14:38 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7702-gllmg-musl=m.gmane.org@lists.openwall.com Mon May 18 22:14:37 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 1YuRQq-0000fu-UU for gllmg-musl@m.gmane.org; Mon, 18 May 2015 22:14:37 +0200 Original-Received: (qmail 1811 invoked by uid 550); 18 May 2015 20:14:35 -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 1790 invoked from network); 18 May 2015 20:14:35 -0000 Content-Disposition: inline In-Reply-To: <20150518201043.GX17573@brightrain.aerifal.cx> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:7690 Archived-At: --f+W+jCU1fRNres8c Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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. Rich --f+W+jCU1fRNres8c Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="reprocess_rela.diff" diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c index 7c92ef6..93595a0 100644 --- a/src/ldso/dynlink.c +++ b/src/ldso/dynlink.c @@ -281,7 +281,7 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri } int gotplt = (type == REL_GOT || type == REL_PLT); - if (dso->rel_update_got && !gotplt) continue; + if (dso->rel_update_got && !gotplt && stride==2) continue; addend = stride>2 ? rel[2] : gotplt || type==REL_COPY ? 0 --f+W+jCU1fRNres8c--