From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31959 invoked by alias); 14 Aug 2008 17:16:44 -0000 Received: (qmail 31946 invoked by uid 22791); 14 Aug 2008 17:16:42 -0000 X-Spam-Check-By: sourceware.org Received: from mtagate8.de.ibm.com (HELO mtagate8.de.ibm.com) (195.212.29.157) by sourceware.org (qpsmtpd/0.31) with ESMTP; Thu, 14 Aug 2008 17:16:01 +0000 Received: from d12nrmr1607.megacenter.de.ibm.com (d12nrmr1607.megacenter.de.ibm.com [9.149.167.49]) by mtagate8.de.ibm.com (8.13.8/8.13.8) with ESMTP id m7EHFYYw296866 for ; Thu, 14 Aug 2008 17:15:34 GMT Received: from d12av02.megacenter.de.ibm.com (d12av02.megacenter.de.ibm.com [9.149.165.228]) by d12nrmr1607.megacenter.de.ibm.com (8.13.8/8.13.8/NCO v9.0) with ESMTP id m7EHFXaV4018270 for ; Thu, 14 Aug 2008 19:15:33 +0200 Received: from d12av02.megacenter.de.ibm.com (loopback [127.0.0.1]) by d12av02.megacenter.de.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m7EHFXxT011888 for ; Thu, 14 Aug 2008 19:15:33 +0200 Received: from tuxmaker.boeblingen.de.ibm.com (tuxmaker.boeblingen.de.ibm.com [9.152.85.9]) by d12av02.megacenter.de.ibm.com (8.12.11.20060308/8.12.11) with SMTP id m7EHFX9E011883; Thu, 14 Aug 2008 19:15:33 +0200 Message-Id: <200808141715.m7EHFX9E011883@d12av02.megacenter.de.ibm.com> Received: by tuxmaker.boeblingen.de.ibm.com (sSMTP sendmail emulation); Thu, 14 Aug 2008 19:15:33 +0200 Subject: Re: [rfc] Fix problem with (maybe) non-relocated .opd section on powerpc64-linux To: drow@false.org (Daniel Jacobowitz) Date: Thu, 14 Aug 2008 17:16:00 -0000 From: "Ulrich Weigand" Cc: gdb-patches@sourceware.org In-Reply-To: <20080516204224.GA10387@caradoc.them.org> from "Daniel Jacobowitz" at May 16, 2008 04:42:24 PM X-Mailer: ELM [version 2.5 PL2] MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2008-08/txt/msg00367.txt.bz2 Daniel Jacobowitz wrote: > On Fri, May 16, 2008 at 10:35:14PM +0200, Ulrich Weigand wrote: > > Thinking about this, it seems this would mean that function descriptors > > cannot work in kernel modules even today: add-symbol-file solely adds > > an objfile (with obj_sections and so on); it does not modify the target > > and its section table. Right? > > Sounds like you're right. I have never tried it, though many of our > customers use KGDB; perhaps not the ones who use PPC64. Another patch that I didn't get to work on for a while ... Given that it seems object files / kernel modules will not work with the current setup anyway, and the patch I originally proposed does fix a serious problem with Linux shared libraries in some cases, I'd like to just apply that patch. Here's an updated version with additional comments to summarize this discussion. Retested on powerpc64-linux. Any objections to installing this patch? Bye, Ulrich ChangeLog: * ppc-linux-tdep.c (ppc64_linux_convert_from_func_ptr_addr): Read and manually relocate .opd contents from BFD instead of reading them from target memory. diff -urNp gdb-orig/gdb/ppc-linux-tdep.c gdb-head/gdb/ppc-linux-tdep.c --- gdb-orig/gdb/ppc-linux-tdep.c 2008-05-26 19:48:46.000000000 +0200 +++ gdb-head/gdb/ppc-linux-tdep.c 2008-08-14 18:00:17.398719879 +0200 @@ -601,7 +601,36 @@ ppc64_linux_convert_from_func_ptr_addr ( /* Check if ADDR points to a function descriptor. */ if (s && strcmp (s->the_bfd_section->name, ".opd") == 0) - return get_target_memory_unsigned (targ, addr, 8); + { + /* There may be relocations that need to be applied to the .opd + section. Unfortunately, this function may be called at a time + where these relocations have not yet been performed -- this can + happen for example shortly after a library has been loaded with + dlopen, but ld.so has not yet applied the relocations. + + To cope with both the case where the relocation has been applied, + and the case where it has not yet been applied, we do *not* read + the (maybe) relocated value from target memory, but we instead + read the non-relocated value from the BFD, and apply the relocation + offset manually. + + This makes the assumption that all .opd entries are always relocated + by the same offset the section itself was relocated. This should + always be the case for GNU/Linux executables and shared libraries. + Note that other kind of object files (e.g. those added via + add-symbol-files) will currently never end up here anyway, as this + function accesses *target* sections only; only the main exec and + shared libraries are ever added to the target. */ + + gdb_byte buf[8]; + int res; + + res = bfd_get_section_contents (s->bfd, s->the_bfd_section, + &buf, addr - s->addr, 8); + if (res != 0) + return extract_unsigned_integer (buf, 8) + - bfd_section_vma (s->bfd, s->the_bfd_section) + s->addr; + } return addr; } -- Dr. Ulrich Weigand GNU Toolchain for Linux on System z and Cell BE Ulrich.Weigand@de.ibm.com