From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 43240 invoked by alias); 10 Oct 2015 02:58:07 -0000 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 Received: (qmail 43227 invoked by uid 89); 10 Oct 2015 02:58:06 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.1 required=5.0 tests=AWL,BAYES_00,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail-io0-f179.google.com Received: from mail-io0-f179.google.com (HELO mail-io0-f179.google.com) (209.85.223.179) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Sat, 10 Oct 2015 02:58:04 +0000 Received: by ioii196 with SMTP id i196so108366035ioi.3 for ; Fri, 09 Oct 2015 19:58:01 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.107.132.144 with SMTP id o16mr18231863ioi.31.1444445881773; Fri, 09 Oct 2015 19:58:01 -0700 (PDT) Received: by 10.36.133.5 with HTTP; Fri, 9 Oct 2015 19:58:01 -0700 (PDT) In-Reply-To: References: <20151002213227.GA3602@adacore.com> <20151006165157.GA3341@adacore.com> <20151010000433.GB3341@adacore.com> Date: Sat, 10 Oct 2015 02:58:00 -0000 Message-ID: Subject: Re: AIX DWARF debugging sections From: David Edelsohn To: Doug Evans , Joel Brobecker , Tristan Gingold Cc: GDB Patches Content-Type: text/plain; charset=UTF-8 X-SW-Source: 2015-10/txt/msg00121.txt.bz2 On Fri, Oct 9, 2015 at 8:24 PM, Doug Evans wrote: > On Fri, Oct 9, 2015 at 5:04 PM, Joel Brobecker > wrote: >> >> > >>> That's what I have been trying to do, but I don't see any evidence >> > >>> that GCC emits it, or that binutils handles it. So the answer must >> > >>> lie somewhere on the system side. David? >> > >> >> > >> The official answer from IBM XLC is the section is for both >> > >> .debug_macinfo and .debug_macro >> > >> >> > >> For DWARF4 and below, the dwmac section corresponds to >> > >> .debug_macinfo. >> > >> For DWARF5 and above, the dwmac section corresponds to .debug_macro. >> > >> >> > >> XLC currently does not generate any macro debugging information for >> > >> DWARF4. >> > > >> > > Huh. >> > > Let's make sure this is documented in the code. >> > >> > Is the following sufficient or you would like more exposition? >> > >> > diff --git a/gdb/xcoffread.c b/gdb/xcoffread.c >> > index 0d49751..86d4ca4 100644 >> > --- a/gdb/xcoffread.c >> > +++ b/gdb/xcoffread.c >> > @@ -159,11 +159,11 @@ static const struct dwarf2_debug_sections >> > dwarf2_xcoff_names = { >> > { ".dwabrev", NULL }, >> > { ".dwline", NULL }, >> > { ".dwloc", NULL }, >> > - { NULL, NULL }, /* debug_macinfo */ >> > - { NULL, NULL }, /* debug_macro */ >> > + { ".dwmac", NULL }, /* debug_macinfo for DWARF4 and below */ >> > + { ".dwmac", NULL }, /* debug_macro for DWARF5 and above */ >> >> Looking at the code in GDB reading the DWARF sections, I am a little >> uncomfortable having two entries for 2 sections sharing the same name. >> I don't have a full grasp of that code, so maybe things would be fine, >> but I'm not sure. Doug has more experience with this code, so might >> know better. > > > > Yeah, I'm worried that the two are incompatible, > and thus using the same name for both will be problematic, > but I haven't found time to verify. > > >> >> >> In the meantime, I started exploring a bit on the GCC side. I have >> been using GCC 4.9, which I think is an interesting reference, >> because not super recent. What I have found is that, unless you >> use -gstrict-dwarf, GCC generates a .debug_macro section. You have >> to use -gstrict-dwarf to get the older .debug_macinfo format. >> >> The bad new is: once assembled using GNU as, the section name >> in the object file is .dwmacro, not .dwmac. As for the .debug_macinfo >> section, it gets renamed to .dwmacif. Those are the GNU as section names invented by Adacore, not the AIX as section names and not used by any tools outside of Adacore. This explanation refers to private patches from Adacore and not the current support in GCC. >> >> I'm not really sure how to best proceed, here. On the one hand, >> IBM can be considered the authority on these kinds of questions. >> On the other hand, GDB being a GNU tool, we should probably make >> it easier to debug code produced by GNU tools rather than by >> propriatery ones... It's particularly tempting since GNU as >> has chosen different section names, which seems to be a better >> choice to me, and also happens to make it easier on the code. > > > Agreed. Not agreed. AIX has a definition of DWARF on the platform. Adacore invented an incompatible definition of DWARF on AIX (and has known about the correct definition since 2011). How can GDB developers argue for conformance with various standards, but ignore the definitions and documentation of AIX? GNU as and ld are not used outside of Adacore. Everyone discussing what to do for the platform and what is possible on the platform apparently is unaware of the general use of the GNU Toolchain on the platform. The last I heard, Adacore had private patches for GNU as and GNU that they had not contributed and the patches were just enough for the needs of Adacore, not a general substitute for AIX as and AIX ld. Since my initial conversations with Adacore in 2011, Olivier and Tristan assured me that they would support the AIX .dwsect DWARF sections in the tools. Now Adacore seems to be disregarding that agreement. DWARF on AIX isn't a private protocol between GCC and GDB. XLC produces executables and libraries following the AIX DWARF standard and section naming. GDB must follow the AIX DWARF standard to be able to interpret debugging information produced by XLC. > >> >> >> Perhaps what we could do is handle it at the binutils level, >> and pretend that ".dwmac" is actually ".dwmacro" or ".dwmacif" >> depending on the compilation unit's DWARF version. Then GDB >> would be modified to handle the names chosen on the GNU side. > > > > Possible alright. > It feels a bit subtle, > Can we wait to here from IBM before going with this? If everyone wants GDB to have an additional Adacore mode, that's fine, but that's not DWARF on AIX. .dwmacro and .dwmacif can be GNU extensions used by Adacore, but they are not appropriate as a general solution. GNU as and ld are not used to build applications on AIX, other than Adacore. Any solution predicated on binutils is not a general solution. AIX XLC apparently will not utilize .dwmac macro section until DWARF5 to encore the .debug_macro section, so GCC and GDB should utilize it as .debug_macro and not produce or consume .debug_macinfo. Thanks, David