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Tue, 25 Oct 2022 13:54:31 +0000 Message-ID: <4f93b1b5-7052-bdd4-8dac-761b2ff1e224@arm.com> Date: Tue, 25 Oct 2022 14:54:30 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH] [Arm] Remove dead FPA code Content-Language: en-US To: Pedro Alves , John Baldwin , gdb-patches@sourceware.org, David Spickett References: <20220920123012.189293-1-luis.machado@arm.com> <73479562-ab47-dfbf-aadc-7a2203c0f0e4@FreeBSD.org> <56653c70-593a-4b8d-ddf7-52f7dd0608f7@arm.com> <1946bc74-8270-23c4-9483-702b9dbc03de@FreeBSD.org> <3cb2d818-83e8-4e2d-5e1b-9b555d1a2217@arm.com> <1003e65d-50fe-8aed-4d98-d06833d27011@palves.net> <42083a0b-9723-8bde-470a-247fbb0740eb@palves.net> From: Luis Machado In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO4P123CA0167.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:18a::10) To VI1PR08MB3919.eurprd08.prod.outlook.com (2603:10a6:803:c4::31) MIME-Version: 1.0 X-MS-TrafficTypeDiagnostic: VI1PR08MB3919:EE_|AS8PR08MB9573:EE_|DBAEUR03FT053:EE_|PAVPR08MB9116:EE_ X-MS-Office365-Filtering-Correlation-Id: 78d6bdfb-e565-4932-15e6-08dab690791e x-checkrecipientrouted: true NoDisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Oct 2022 13:54:44.9907 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 78d6bdfb-e565-4932-15e6-08dab690791e X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: DBAEUR03FT053.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAVPR08MB9116 X-Spam-Status: No, score=-6.3 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,KAM_DMARC_NONE,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,TXREP,UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 10/13/22 10:40, Luis Machado via Gdb-patches wrote: > On 10/13/22 09:29, Pedro Alves wrote: >> >> >> On 2022-10-13 8:23 a.m., Luis Machado wrote: >>> On 10/10/22 15:58, Pedro Alves wrote: >>>> On 2022-10-05 9:26 a.m., Luis Machado wrote: >>>> >>>>> Yeah, that's what I was worried about. Register discoveries without XML are not great, and more recently debugging stubs have been >>>>> exposing more system registers. Having to consider FPA (which was *removed* 10 years ago from GCC, but fell in disuse before then) is not >>>>> acceptable at this point. >>>>> >>>>> If those debugging stubs want to skip XML, I think it would be reasonable for them to at least update the expected 'g' packet to contain just >>>>> the basic registers, with CPSR as 16. >>>>> >>>>> That might need some coordination. I can coordinate this from the Linux Kernel's side, but I never dealt with the BSD kernels. >>>> >>>> I'm not seeing much point in this: >>>> >>>> #1 - If the remote side supplies XML, then the register number doesn't really matter, GDB auto-maps the numbers. >>>> >>>> #2 - If the remote side doesn't supply XML, then you're just setting up for a world of coordination pain for no benefit. >>>> >>>> In GDB, to keep things working, we just have to keep the FPA register number hole in place.  That's hardly causing >>>> any maintenance burden, IMO.  We just have to have comments in place explaining why we have them. >>> >>> Based on a recent thread with the Arm Linux Kernel maintainer, he finds it reasonable to make kgdb >>> return XML data and to keep a compatibility layer (the g guesses) going for a reasonable amount of >>> time, after which we can retire the guesses and drop the code. >> >> Good.  Of course, the Linux kernel isn't going to be the only remote server or stub out there. >> > > No, but most of the probes have been updated to use XML over the years. Yes, there is an unknown list of old > probes and hardware out there potentially not using XML. I haven't seen any such issues reported against the > GDB bugzilla though, which is good either way. > >>> >>> It is not clear when we'll drop the compatibility layer, but at least we can get some traction towards >>> making targets use XML and maybe add some deprecation warning to the g packet guesses. If we keep the code as-is, >>> there is no incentive to update targets using old mechanisms. >> >> Deprecation warnings makes sense to me.  Much more user-friendly than flat out removing the guesses without a warning >> period, and/or changing the non-XML g/G packet layout. >> >> The (unwritten) policy for as long as I'm worked on GDB has always been that you don't change the hardcoded g/G packet >> layout, ever.  You can only grow it.  Or use XML. > > Sure. But no longer required for XML-based data. > >> >> While we can push new versions of tools to switch to XML, the older versions will still be out there.  Stubs can >> be embedded in devices that aren't going to update easily or at all.  Is it a good idea to to cause them pain?  IMHO, no. >> >> Note, for the FPA removal, you should send an email to gdb@ as well, see here for the obsoleting procedure: >> >>    https://sourceware.org/gdb/wiki/Internals%20Obsoleting-code >> > > Do you want that procedure followed completely, including the week waiting? I also seem to recall a different policy, where we > deprecate something for a particular release and then remove on the next one. Before I refresh this patch, did you have thoughts on the above?