From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 58424 invoked by alias); 11 Apr 2017 10:16:17 -0000 Mailing-List: contact elfutils-devel-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Post: List-Help: List-Subscribe: Sender: elfutils-devel-owner@sourceware.org Received: (qmail 58404 invoked by uid 89); 11 Apr 2017 10:16:16 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Checked: by ClamAV 0.99.2 on sourceware.org X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.5 required=5.0 tests=AWL,BAYES_00,MISSING_HEADERS,RCVD_IN_DNSWL_NONE,SPF_HELO_PASS,SPF_PASS autolearn=no version=3.3.2 spammy=H*RU:sk:mail-he, Hx-spam-relays-external:sk:mail-he X-Spam-Status: No, score=-1.5 required=5.0 tests=AWL,BAYES_00,MISSING_HEADERS,RCVD_IN_DNSWL_NONE,SPF_HELO_PASS,SPF_PASS autolearn=no version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on sourceware.org X-Spam-Level: X-HELO: EUR01-HE1-obe.outbound.protection.outlook.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=qtcompany.onmicrosoft.com; s=selector1-qt-io; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=nDvytjgIfL+v79jmDxjbpSU+whz6TI3MT1SHYnaqU8Y=; b=SQbQ/M6mVHxEGK/i4ged8zAcz0tpVQMQin/IsMq/DvhEHeeD+zGtBs+tMWoq8kOcB0nWcJPM/xkM4pdrOvM/AxlocfS1UNGY3mTudOXCOzGOFk85Q0Ygnd8L1Yo1PSfZ/jHhVXumwbdjQgQ6zLo5oR2xseJ0cUdQ5dKfOmj4Wmw= Authentication-Results: sourceware.org; dkim=none (message not signed) header.d=none;sourceware.org; dmarc=none action=none header.from=qt.io; Subject: Re: frame unwinding patches References: <1487201610-8381-1-git-send-email-mark@klomp.org> <3915502.JGE1jdPxOT@milian-kdab2> <75e83a7d-b372-3436-ba7a-3a49900e92dd@qt.io> <20170403211516.GB9584@stream> <1491560851.8380.162.camel@klomp.org> CC: From: Ulf Hermann Message-ID: Date: Tue, 11 Apr 2017 10:16:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.6.0 MIME-Version: 1.0 In-Reply-To: <1491560851.8380.162.camel@klomp.org> Content-Type: text/plain; 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Even with some sanity checks it is hard to know whether > you are doing a correct unwind. gdb gets away with it through pretty > advanced frame sniffers, which take a lot of low-level compiler > generation knowledge to get correct (and even then...). You only restore > the pc, stack and frame pointer registers (maybe incorrectly). So > afterwards, even if you got valid CFI data you might be stuck. Yes, especially with mixed stack traces, where part of the stack has CFI and part of it doesn't, we quickly run into guesswork. I've regenerated the binaries as suggested, with the result being that raise() from libc actually has CFI, but doesn't set a frame pointer. So, the frame pointer unwinder can find raise() in the link register, but it sets up the FP register with the wrong value. Then raise() is unwound using CFI, which mixes up the registers some more. At that point we're lost. I don't see an easy way out of this. I will keep a version of the frame unwinding for perfparser as it's still better than not unwinding at all, but I do understand that it's not really suitable for mainline elfutils. br, Ulf