From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 111114 invoked by alias); 1 Mar 2018 20:18:18 -0000 Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org Received: (qmail 111086 invoked by uid 89); 1 Mar 2018 20:18:17 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM,HTML_MESSAGE,RCVD_IN_DNSWL_NONE,SPF_PASS autolearn=ham version=3.3.2 spammy=Roman, 9f, from, roman X-HELO: mail-lf0-f45.google.com Received: from mail-lf0-f45.google.com (HELO mail-lf0-f45.google.com) (209.85.215.45) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 01 Mar 2018 20:18:14 +0000 Received: by mail-lf0-f45.google.com with SMTP id g72so10227892lfg.3 for ; Thu, 01 Mar 2018 12:18:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=as1eZvJmlpzwo9dFHuMiO2TJAHR1f2x1eWuPoI/8Kr4=; b=oJPNq/28i0Gbl2uWShc9OVxjTU9hkIF+Gt1tfofZ7I+nMUtXWLjoFHnrkJBk+6Ujuw nHx8Cu9SrciowsRcAOaKJif2mO62PCUku7Equ5m7+KGdTijVVyFDM95+eoFmCCCaXSkz MW0CxtgUjkREBuoR38pK6hzSNSv10SRVCAhaxBcqNyM19lk5Q3JODfRrey/kzXSyqq4R quNgMMuyAeHOMrKiOi8SRhOsbEL6Ew3kXR5M33psKh4gJNuz0tWg5mcYbuH6Jcny/kzS Kv+hX+WtJPUNPEX/Vmq67olGwZQKEjAKemKf8x88ib8yIvfL1zEZVTLT193vj2Hpnt+O S7IA== X-Gm-Message-State: AElRT7Eqiuoew1L2lWW6CeEeif5akhXQYUoHLhZ7kMKTUXTPL/oXqEWK Dqoz0pinlerys3r+KRdRGEPaoHACimU185N2lnU= X-Google-Smtp-Source: AG47ELsIlJhKW+Eu+c5wwWXjZMhsJ4rDnrBgPMnGyzZlmmfsGgHnBV3SH2zCMiOF8d9+1NnDtVzfHCD45URF+vmBdVs= X-Received: by 10.25.0.19 with SMTP id 19mr2207171lfa.69.1519935492062; Thu, 01 Mar 2018 12:18:12 -0800 (PST) MIME-Version: 1.0 Received: by 10.46.62.7 with HTTP; Thu, 1 Mar 2018 12:18:11 -0800 (PST) In-Reply-To: References: <1517667601.3405.123.camel@gnu.org> <1b58e2df-5425-4f22-510c-d2e9f51040ba@polymtl.ca> <39845077-6bdf-f60d-9bfc-a491e7fa4fc7@gmail.com> <132fbd97-4f0d-020f-1c0f-1d4097800233@polymtl.ca> From: Roman Popov Date: Thu, 01 Mar 2018 20:18:00 -0000 Message-ID: Subject: Re: gdb 8.x - g++ 7.x compatibility To: Richard Biener Cc: Simon Marchi , Martin Sebor , Manfred , gdb@sourceware.org, GCC Development Content-Type: text/plain; charset="UTF-8" X-IsSubscribed: yes X-SW-Source: 2018-03/txt/msg00004.txt.bz2 Is there any progress on this problem? I'm not familiar with G++ , but I have little experience with LLVM. I can try make LLVM emitting mangled names to DW_AT_name, instead of demangled ones. This way GDB can match DW_AT_name against RTTI. And for display it can call abi::__cxa_demangle(name, NULL, NULL, &status), from #include . Will it work? Thanks, Roman 2018-02-08 7:05 GMT-08:00 Richard Biener : > On Mon, Feb 5, 2018 at 6:06 AM, Simon Marchi > wrote: > > Hi Martin, > > > > Thanks for the reply. > > > > On 2018-02-04 02:17 PM, Martin Sebor wrote: > >> Printing the suffix is unhelpful because it leads to unnecessary > >> differences in diagnostics (even in non-template contexts). For > >> templates with non-type template parameters there is no difference > >> between, say A<1>, A<1U>, A<(unsigned) 1>, or even A when > >> Green is an enumerator that evaluates to 1, so including the suffix > >> serves no useful purpose. > > > > This is the part I don't understand. In Roman's example, spelling > > foo<10> and foo<10u> resulted in two different instantiations of the > > template, with different code. So that means it can make a difference, > > can't it? > > > >> In the GCC test suite, it would tend to > >> cause failures due to differences between the underlying type of > >> common typedefs like size_t and ptrdiff_t. Avoiding these > >> unnecessary differences was the main motivation for the change. > >> Not necessarily just in the GCC test suite but in all setups that > >> process GCC messages. > > > > Ok, I understand. > > > >> I didn't consider the use of auto as a template parameter but > >> I don't think it changes anything. There, just like in other > >> contexts, what's important is the deduced types and the values > >> of constants, not the minute details of how they are spelled. > > > > Well, it seems like using decltype on a template constant value is > > a way to make the type of constants important, in addition to their > > value. I know the standard seems to say otherwise (what Manfred > > quoted), but the reality seems different. I'm not a language expert > > so I can't tell if this is a deficiency in the language or not. > > > >> That said, it wasn't my intention to make things difficult for > >> the debugger. > > > > I hope so :). > > > >> But changing GCC back to include the suffix, > >> even just in the debug info, isn't a solution. There are other > >> compilers besides GCC that don't emit the suffixes, and there > >> even are some that prepend a cast to the number, so if GDB is > >> to be usable with all these kinds of producers it needs to be > >> able to handle all of these forms. > > > > As I said earlier, there are probably ways to make GDB cope with it. > > The only solution I saw (I'd like to hear about other ones) was to make > > GDB ignore the template part in DW_AT_name and re-build it from the > > DW_TAG_template_* DIEs in the format it expects. It can already do > > that somewhat, because, as you said, some compilers don't emit > > the template part in DW_AT_name. > > > > Doing so would cause major slowdowns in symbol reading, I've tried it > > for the sake of experimentation/discussion. I have a patch available > > on the "users/simark/template-suffix" branch in the binutils-gdb > > repo [1]. It works for Roman's example, but running the GDB testsuite > > shows that, of course, the devil is in the details. > > > > Consider something like this: > > > > template > > struct foo { virtual ~foo() {} }; > > > > int n; > > > > int main () > > { > > foo<&n> f; > > } > > > > > > The demangled name that GDB will be looking up is "foo<&n>". The > > debug info about the template parameter only contains the resulting > > address of n (the value of &n): > > > > <2>: Abbrev Number: 11 (DW_TAG_template_value_param) > > DW_AT_name : P > > DW_AT_type : <0x1ac> > > DW_AT_location : 10 byte block: 3 34 10 60 0 0 0 0 0 9f > (DW_OP_addr: 601034; DW_OP_stack_value) > > > > I don't see how GDB could reconstruct the "&n" in the template, so > > that's where my idea falls short. > > For other reasons I've always wanted sth like > > DW_OP_addr; DW_OP_name: n; DW_OP_stack_value > > thus put symbolical expressions in locations and have the consumer look > them up > (in context obviously). That way gdb can also choose to print foo > instead of > foo<1> or foo<>. > > Of course that needs DWARF extensions. > > Richard. > > > Simon > > > > [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git; > a=shortlog;h=refs/heads/users/simark/template-suffix >