From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 108727 invoked by alias); 24 Feb 2016 16:31:52 -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 108711 invoked by uid 89); 24 Feb 2016 16:31:52 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.8 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE,SPF_PASS autolearn=ham version=3.3.2 spammy=trial 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; Wed, 24 Feb 2016 16:31:51 +0000 Received: from svr-orw-fem-06.mgc.mentorg.com ([147.34.97.120]) by relay1.mentorg.com with esmtp id 1aYcLs-0003KO-3v from Don_Breazeal@mentor.com for gdb-patches@sourceware.org; Wed, 24 Feb 2016 08:31:48 -0800 Received: from [172.30.3.23] (147.34.91.1) by svr-orw-fem-06.mgc.mentorg.com (147.34.97.120) with Microsoft SMTP Server (TLS) id 14.3.224.2; Wed, 24 Feb 2016 08:31:46 -0800 Subject: Re: [PATCH] Eliminate -var-create error for optzd ptr to struct To: "Gustavo, Luis" , "gdb-patches@sourceware.org" References: <1456273154-28629-1-git-send-email-donb@codesourcery.com> <56CD03F5.6080505@codesourcery.com> From: Don Breazeal Message-ID: <56CDDAEE.1030504@codesourcery.com> Date: Wed, 24 Feb 2016 16:31:00 -0000 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <56CD03F5.6080505@codesourcery.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-IsSubscribed: yes X-SW-Source: 2016-02/txt/msg00733.txt.bz2 On 2/23/2016 5:14 PM, Gustavo, Luis wrote: > On 02/23/2016 09:19 PM, Don Breazeal wrote: >> Problem: >> This patch eliminates an error thrown when accessing the value of a >> pointer to a structure where the pointer has been optimized out. >> The error shows up as the rather ugly value of the pointer variable >> in Eclipse. >> >> With this change such an access will return "" like >> other optimized out variables. We should throw an error when >> dereferencing an optimized-out pointer, but not when just looking >> at its value. >> >> Cause: >> The error only occurs when '-gdb-set print object on' has been set. >> This setting requires GDB to "identify the actual (derived) type of >> the object rather than the declared type". Part of this process >> is to dereference the pointer in order to get the type of the thing >> that is pointed-to. Since the pointer has been optimized out, this >> is impossible, and an error is thrown. >> >> Fix: >> The fix is to simply ignore the 'print object on' setting for >> pointers or references to structures when they have been optimized >> out. This means we just get the declared type instead of the actual >> type, because in this case that's the best that we can do. >> >> Results: >> Attempts to dereference the optimized-out pointer using -var-create >> or -data-evaluate-expression will throw an error, but a dereference >> using -var-evaluate-expression will return an empty value. To be >> consistent, this last case would also throw an error. I looked into >> this some, enough to confirm that there isn't an obvious fix. Given >> that my goal is just to eliminate the unnecessary error, I stopped here. >> >> I'm working on setting things in motion for a patch to Eclipse that >> recognizes optimized-out pointer-to-struct in this scenario and >> prevents any subsequent attempt to dereference it from that end. >> >> Testing: >> I looked at creating a test case for this, but so far haven't been >> able to create anything general enough to include in the test suite. >> >> Tested on bare-metal powerpc board with Linux x86_64 host. >> >> OK? >> >> thanks >> --Don >> >> gdb/ChangeLog: >> 2016-02-23 Don Breazeal >> >> * gdb/value.c (value_actual_type): Ignore the 'print object >> on' setting for pointers and references to structures. >> >> --- >> gdb/value.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/gdb/value.c b/gdb/value.c >> index 738b2b2..50e4f8a 100644 >> --- a/gdb/value.c >> +++ b/gdb/value.c >> @@ -1203,9 +1203,10 @@ value_actual_type (struct value *value, int resolve_simple_types, >> /* If result's target type is TYPE_CODE_STRUCT, proceed to >> fetch its rtti type. */ >> if ((TYPE_CODE (result) == TYPE_CODE_PTR >> - || TYPE_CODE (result) == TYPE_CODE_REF) >> + || TYPE_CODE (result) == TYPE_CODE_REF) > > Is this just a formatting change? Yes. I should have documented that in the ChangeLog. > >> && TYPE_CODE (check_typedef (TYPE_TARGET_TYPE (result))) >> - == TYPE_CODE_STRUCT) >> + == TYPE_CODE_STRUCT >> + && !value_optimized_out (value)) >> { >> struct type *real_type; >> > > Otherwise looks OK to me. Thanks for the review, Luis. > > As for the testcase, how about one that creates a few pointer variables > (to basic types, structures, arrays and other meaningful ones) and tries > to print their original values with the "print object" enabled. This > would be in MI mode, of course. > > I'd expect the error to be thrown in an unpatched gdb and a out> string for the patched debugger. > The main problem so far has been to get the compiler to optimize out the variables that I want it to optimize out, with a target that is generic enough that I can generate some assembly code that will run on something other than a specific version of a CPU. Trial and error.