From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 103344 invoked by alias); 21 Nov 2016 16:37:24 -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 102740 invoked by uid 89); 21 Nov 2016 16:37:23 -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,SPF_PASS autolearn=ham version=3.3.2 spammy=riscv, RISCV, risc-v, RISC-V X-HELO: sesbmg22.ericsson.net Received: from sesbmg22.ericsson.net (HELO sesbmg22.ericsson.net) (193.180.251.48) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 21 Nov 2016 16:37:13 +0000 Received: from ESESSHC011.ericsson.se (Unknown_Domain [153.88.183.51]) by (Symantec Mail Security) with SMTP id 9D.D1.06466.7B223385; Mon, 21 Nov 2016 17:37:11 +0100 (CET) Received: from EUR01-HE1-obe.outbound.protection.outlook.com (153.88.183.145) by oa.msg.ericsson.com (153.88.183.51) with Microsoft SMTP Server (TLS) id 14.3.319.2; Mon, 21 Nov 2016 17:36:50 +0100 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=antoine.tremblay@ericsson.com; Received: from elxa4wqvvz1 (192.75.88.130) by VI1PR0701MB1886.eurprd07.prod.outlook.com (10.167.197.22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id 15.1.734.2; Mon, 21 Nov 2016 16:36:48 +0000 References: User-agent: mu4e 0.9.17; emacs 24.5.50.1 From: Antoine Tremblay To: Tim Newsome CC: gdb Subject: Re: read target register to decide breakpoint size Message-ID: In-Reply-To: Date: Mon, 21 Nov 2016 16:37:00 -0000 MIME-Version: 1.0 Content-Type: text/plain X-ClientProxiedBy: BN4PR15CA0029.namprd15.prod.outlook.com (10.164.54.167) To VI1PR0701MB1886.eurprd07.prod.outlook.com (10.167.197.22) X-Microsoft-Exchange-Diagnostics: 1;VI1PR0701MB1886;2:FRyHF1AcTCFVh+KSCECNMtNwKHUYb+5VxO4W2C4sRQkbTHWmbRjhNC2mUCIkIHW0f2EbOJAxGWP8C3BfsdMXs3Vesl3I3f6j3fhySJcVnl7VSiz6bZOk6v82VGGKefRcg5aPbN05c60m1/7qT2kEwZZAxUIDJdm1cZmY1F+T0cI=;3:sVgkMlvZqbdtilW9nWobpxPz3afGXzqLlV7Uxaf0YuX4mHQaN6B5jZw1CjbXKifnZKSG4xLoi4HcvpERjaw3mV/lfEFR3+YV6L/we9mS1CICooSMbgHyJLFddN81sqc3+Q8MqKpoweTq6oBTzM8vtxKmDYEbm8F63HsTOEaILs0= X-MS-Office365-Filtering-Correlation-Id: baaf8999-903a-4b71-b348-08d4122c9771 X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001);SRVR:VI1PR0701MB1886; 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Any given RISC-V core may > support a compressed instruction set (2 bytes per instruction as > opposed to 4). There are corresponding 2-byte and 4-byte breakpoint > instructions. On cores that support the compressed instruction set it > is safe to just always use the 2-byte version, and there is a register > I can read to tell me whether the compressed instruction set is > supported. What I would like to do is read (and cache) that register > when breakpoint size is determined. That seems more robust than making > a decision based on ELF info, which may not reflect what is actually > being executed. > > Is that a good idea? Are there examples of operations that read target > registers to complete? Yes actually you can check how ARM does it, it has the same kind of problem with 3 breakpoints you can set for thumb, thumb2 and arm instruction sets. See arm-tdep.c:arm_sw_breakpoint_from_kind and arm_breakpoint_kind_from_current_state This is called in breakpoint.c:breakpoint_kind and it can use a register to make the decision from the current state of that register. So possibly just implementing the sw_breakpoint_from_kind and breakpoint_kind_from_current state would be ok your you. Regards, Antoine Tremblay