From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gproxy1-pub.mail.unifiedlayer.com (gproxy1-pub.mail.unifiedlayer.com [69.89.25.95]) by sourceware.org (Postfix) with ESMTPS id DCBD83858D32 for ; Sat, 21 Jan 2023 17:48:23 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org DCBD83858D32 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=tromey.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tromey.com Received: from cmgw10.mail.unifiedlayer.com (unknown [10.0.90.125]) by progateway3.mail.pro1.eigbox.com (Postfix) with ESMTP id 4F8B9100483D6 for ; Sat, 21 Jan 2023 17:48:23 +0000 (UTC) Received: from box5379.bluehost.com ([162.241.216.53]) by cmsmtp with ESMTP id JHyZptPCKFqSRJHyZpDHlL; Sat, 21 Jan 2023 17:48:23 +0000 X-Authority-Reason: nr=8 X-Authority-Analysis: v=2.4 cv=c6Ru/Txl c=1 sm=1 tr=0 ts=63cc2567 a=ApxJNpeYhEAb1aAlGBBbmA==:117 a=ApxJNpeYhEAb1aAlGBBbmA==:17 a=dLZJa+xiwSxG16/P+YVxDGlgEgI=:19 a=RvmDmJFTN0MA:10:nop_rcvd_month_year a=Qbun_eYptAEA:10:endurance_base64_authed_username_1 a=CCpqsmhAAAAA:8 a=NEAV23lmAAAA:8 a=jrPOwMmjcJyni8ub5IgA:9 a=ul9cdbp4aOFLsgKbc677:22 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=tromey.com; s=default; h=Content-Type:MIME-Version:Message-ID:In-Reply-To:Date:References :Subject:Cc:To:From:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=wfx9auaOqZkOGRsyGCBjbvShSChKRBqSMYAuJfkHerc=; b=mkSzcIsNTEd0p3K6LHlf84uEsX ArQELakXTFjBst2C2hPiMSNxKhLRCxbsopcbf/PebQNlJf8RockopFPvpxta9Rc/Hn1+/5rJnbU3G OPXGeiJQlkjoV9w8sEL3g6+PB; Received: from 97-122-76-186.hlrn.qwest.net ([97.122.76.186]:40026 helo=prentzel) by box5379.bluehost.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1pJHyY-004IvD-Va; Sat, 21 Jan 2023 10:48:23 -0700 From: Tom Tromey To: Tom de Vries via Gdb-patches Cc: Tom de Vries Subject: Re: [RFC] [gdb/tdep] Assume epilogue unwind info is valid unless gcc < 4.5.0 References: <20230121074807.22032-1-tdevries@suse.de> X-Attribution: Tom Date: Sat, 21 Jan 2023 10:48:20 -0700 In-Reply-To: <20230121074807.22032-1-tdevries@suse.de> (Tom de Vries via Gdb-patches's message of "Sat, 21 Jan 2023 08:48:07 +0100") Message-ID: <87a62blqxn.fsf@tromey.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - box5379.bluehost.com X-AntiAbuse: Original Domain - sourceware.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - tromey.com X-BWhitelist: no X-Source-IP: 97.122.76.186 X-Source-L: No X-Exim-ID: 1pJHyY-004IvD-Va X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 97-122-76-186.hlrn.qwest.net (prentzel) [97.122.76.186]:40026 X-Source-Auth: tom+tromey.com X-Email-Count: 4 X-Source-Cap: ZWx5bnJvYmk7ZWx5bnJvYmk7Ym94NTM3OS5ibHVlaG9zdC5jb20= X-Local-Domain: yes X-Spam-Status: No, score=-3021.5 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,JMQ_SPF_NEUTRAL,KAM_NUMSUBJECT,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_PASS,TXREP 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: >>>>> "Tom" == Tom de Vries via Gdb-patches writes: Tom> Fix these two issues by reversing the burden of proof: Tom> - currently we assume epilogue unwind info is invalid unless we can proof that Tom> gcc >= 4.5.0. Tom> - instead, assume epilogue unwind info is valid unless we can proof that Tom> gcc < 4.5.0. FWIW this approach makes sense to me. It's pretty lame that there's no way to detect this failure from the frame section -- it can't be producer-sniffed and the augmentation strings can't really be changed. gcc 4.5 was released in 2010, and so it's not like we're inconveniencing a lot of users. If needed I guess we could add a user setting to switch this behavior back on. Note there is a similar issue for the prologue, see: https://sourceware.org/bugzilla/show_bug.cgi?id=25696 https://sourceware.org/bugzilla/show_bug.cgi?id=17265 https://sourceware.org/bugzilla/show_bug.cgi?id=21470 Also worth seeing the hilarious: https://github.com/rust-lang/rust/issues/41252#issuecomment-293676579 I think that in this area we should assume the debug info is correct, and keep a list of known-bad producers rather than assuming the debug info is wrong and having a list of known-good ones. Tom> + if (/* In absence of producer information, optimistically assume that we're Tom> + not dealing with gcc < 4.5.0. */ This placement of the comment is pretty weird, it seems fine to just stick it before the 'if'. Tom> + if (cu->producer == nullptr) Tom> + /* In absence of producer information, optimistically assume that we're Tom> + not dealing with gcc < 4.5.0. */ Tom> + cust->set_epilogue_unwind_valid (true); Tom> + if (!producer_is_gcc (cu->producer, nullptr, nullptr)) Normally if there is a comment and a line of code as the consequence of an 'if', we put them both in a block. Anyway I was also thinking that the second one should say 'else if'. Tom