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([2804:14d:8084:9a69::1000]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2fbf98cfd66sm3161147a91.12.2025.02.13.04.25.45 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Feb 2025 04:25:46 -0800 (PST) Message-ID: Date: Thu, 13 Feb 2025 09:25:44 -0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: "gdb-patches@sourceware.org" From: Guinevere Larsen Subject: Follow up to stabs deprecation - AIX regressions X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: tFrkkL7MltE52Ns7c9qfrq3GBaGl7zZsUWEkkLTWg6U_1739449548 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org Hi all, I've been working on the removal of stabs ahead of schedule, and testing what I could test. I noticed that the debug experience in AIX is severely affected by the removal of stabs. The most noticeable things I've seen is: * DWARF reading can sometimes fail in AIX. Currently, reading dwarf for xcoff inferiors is called on it's own, with no warning if dwarf fails (which probably makes sense, considering the default format in aix is still stabs). I added a warning when failing to read dwarf and noticed it being triggered on inferiors compiled with -gdwarf * DWARF reading is also outdated. the dwarf2_xcoff_names struct is missing 4 section names based on IBM docs[1], the one I remember is .dwarnge. * Dealing with C++ classes has 2 obvious issues: when a pointer of an inherited class is downcast, GDB is unable to find members of the original type (that should be accessible), and GDB doesn't quite understand class methods as functions - step will skip method calls - plus a few more issues ado with understanding inheritance, as tested in gdb.cp/casts.exp * Fortran tests can't runto_main. This seems to be a compiler issue, as the fortran_runto_main identifies the main function as MAIN__, but examining the generated dwarf there is no symbol for that. * You just can't call inferior functions by hand. Most of the time, it gets a segfault with a corrupted stack. Considering that this used to work when reading stabs, it feels like the dwarf isn't properly explaining something about the frame that GDB uses to create dummy frames for the hand call, and it looks like it'd require a lot of system knowledge to fix I haven't looked too in-depth into all failures, this is the large-scale patterns and my best attempt at explaining why things are failing how they are. Considering the state that AIX was in before I started testing it (less than 40k passes, and simply compiling with dwarf we can move up to 74.5k), and considering that the current maintainer of AIX is Kevin - who from our conversations remembers very little of how xcoff and aix work - I don't think this would warrant delaying removing stabs, but I think we should be aware of it so that if folks are using AIX, or interested in fixing it, they have until the release of GDB 18 to get the regressions under control. [1] https://www.ibm.com/docs/en/aix/7.3?topic=formats-xcoff-object-file-format -- Cheers, Guinevere Larsen She/Her/Hers