From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 83052 invoked by alias); 9 Jan 2017 19:57:07 -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 83035 invoked by uid 89); 9 Jan 2017 19:57:06 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE,SPF_PASS autolearn=ham version=3.3.2 spammy=our X-HELO: relay1.mentorg.com Received: from relay1.mentorg.com (HELO relay1.mentorg.com) (192.94.38.131) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 09 Jan 2017 19:56:56 +0000 Received: from svr-orw-mbx-03.mgc.mentorg.com ([147.34.90.203]) by relay1.mentorg.com with esmtp id 1cQg3p-0006X9-RN from Luis_Gustavo@mentor.com ; Mon, 09 Jan 2017 11:56:53 -0800 Received: from [172.30.7.42] (147.34.91.1) by svr-orw-mbx-03.mgc.mentorg.com (147.34.90.203) with Microsoft SMTP Server (TLS) id 15.0.1210.3; Mon, 9 Jan 2017 11:56:49 -0800 Reply-To: Luis Machado Subject: Re: [PATCH] Handle loading improper core files gracefully in the mips backend. References: <1452277948-25292-1-git-send-email-lgustavo@codesourcery.com> <5693CE90.1060709@codesourcery.com> <5694F5BC.3050904@redhat.com> <5694FEB8.10406@codesourcery.com> <56950952.2030504@redhat.com> <56951F29.7070000@codesourcery.com> To: "Maciej W. Rozycki" CC: Pedro Alves , , From: Luis Machado Message-ID: Date: Mon, 09 Jan 2017 19:57:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: svr-orw-mbx-01.mgc.mentorg.com (147.34.90.201) To svr-orw-mbx-03.mgc.mentorg.com (147.34.90.203) X-IsSubscribed: yes X-SW-Source: 2017-01/txt/msg00133.txt.bz2 On 01/12/2016 12:30 PM, Maciej W. Rozycki wrote: > On Tue, 12 Jan 2016, Luis Machado wrote: > >>>> The data above leads gdbarch_info_fill to assign default_bfd_arch to >>>> info->bfd_arch_info here: >>>> >>>> /* From the default. */ >>>> if (info->bfd_arch_info == NULL) >>>> info->bfd_arch_info = default_bfd_arch; >>>> >>>> So the core file essentially turns into a mips-compatible core file. >>> >>> Hmmm. I see. I think we can't really change this, given that there >>> are formats that don't have an architecture. Like, e.g., srec: >>> >>> (gdb) file testsuite/gdb.base/intstr2.srec >>> Reading symbols from testsuite/gdb.base/intstr2.srec...(no debugging >>> symbols found)...done. > > Or we could be talking to a live target with no executable selected at > all. This is also why there are settings like `set mips abi ...' > available -- to let the user select the executable model for a target > there's no other source of information about. > >>> I also wonder whether the bfd arch detection couldn't be always >>> compiled in, at least for elf. Why does bfd fail to detect that this >>> is an bfd_arch_i386 file in the first place? > > The mapping between `e_machine' and `bfd_architecture' is only provided > by individual BFD ELF target backends, via the ELF_MACHINE_CODE and > ELF_ARCH macros. > >> It seems bfd also falls back to the default, which is mips in this case. >> >> p bfd_default_vector[0] >> $3 = (const bfd_target *) 0x9beac0 > > Regardless, I'd expect a suitable generic ELF BFD target to be selected, > which is what AFAICT `bfd_check_format' does. It is called by our > `core_open' function and has a `core_file_p' handler, which makes suitable > checks including `e_machine' in particular, except for generic ELF BFD > targets, which are special-cased (and always come last). So in the > absence of specific ELF target support in BFD I'd expect a compatible > generic ELF target to be chosen rather than the default BFD target, which > might be incompatible. > >> Sounds like we have a couple issues. The mips backend not handling weird >> abi/isa combinations and GDB not preventing clearly incompatible core files >> from proceeding further into processing in the target's backend? > > I have given it some thought and came to a conclusion that we should at > least try being consistent. Which means I think we should not try to > handle files within the MIPS backend which would not be passed in the > first place in an `--enable-targets=all' configuration. Rather than > checking `e_machine' explicitly I'd be leaning towards using BFD to detect > such a situation though, perhaps by using a condition like > > if (info.abfd != NULL > && bfd_get_flavour (info.abfd) == bfd_target_elf_flavour > && bfd_get_arch (info.abfd) != bfd_arch_mips) > return NULL; > > (maybe with an additional error message) though ultimately I think it > would make sense to define different BFD architecture codes for file > formats which by definition carry no architecture information and for ones > that do but are not supported. Then for the formers we could continue > selecting the target using the current algorithm and for the latters we'd > just reject them as incompatible with the given backend -- all somewhere > in generic code so that individual target backends do not have to repeat > it all. > > As to ABI, ISA, etc. settings -- these are internal to the MIPS backend, > so its the backend's job to sanitise them. > > Maciej > After quite a while, i'm revisiting this one. Reading the thread once again, is my understanding correct that the first patch is more suitable now? Possibly with some cleanups? https://sourceware.org/ml/gdb-patches/2016-01/msg00134.html Regards, Luis