From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 90071 invoked by alias); 20 Jul 2016 18:46:32 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 90053 invoked by uid 89); 20 Jul 2016 18:46:31 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,SPF_PASS autolearn=ham version=3.3.2 spammy=H*Ad:U*tom, H*r:Unknown, online X-HELO: esa3.dell-outbound.iphmx.com Received: from Unknown (HELO esa3.dell-outbound.iphmx.com) (68.232.153.94) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Wed, 20 Jul 2016 18:46:21 +0000 Received: from ausxipps301.us.dell.com ([143.166.148.223]) by esa3.dell-outbound.iphmx.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 20 Jul 2016 23:46:13 +0500 X-LoopCount0: from 10.175.216.250 From: To: CC: , , Subject: Re: [RFA 5/6] Remove unused variables Date: Wed, 20 Jul 2016 18:46:00 -0000 Message-ID: <261F6870-E91C-4747-8B21-10493AD8550C@dell.com> References: <1465248812-23902-1-git-send-email-tom@tromey.com> <1465248812-23902-6-git-send-email-tom@tromey.com> <87wpl9t4l2.fsf@tromey.com> <87furdnubd.fsf@tromey.com> In-Reply-To: Content-Type: text/plain; charset="us-ascii" Content-ID: <24967AC236884B46B425E36F56BE9826@dell.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-IsSubscribed: yes X-SW-Source: 2016-07/txt/msg00229.txt.bz2 > On Jul 20, 2016, at 2:36 PM, Maciej W. Rozycki wrote: >=20 > ... > Overall with recent and less so improvements to GCC's and other=20 > compilers' optimizers I think these heuristic unwinders have hardly any=20 > value nowadays, they seem unable to get through function prologues=20 > containing arbitrary instructions thrown there by the scheduler. This is= =20 > very annoying in a common case where you interrupt a debuggee in the=20 > middle of a sleeping syscall, with no way to backtrace through stripped=20 > system shared libraries. My experience is that the heuristic unwinders can be made to handle a lot o= f what's thrown at them now, but it takes quite a lot of extra heuristics t= o do so. I have much of this on an internal version. Should I look into m= aking them available? One thing I've done that may not be generally interesting: make the unwinde= rs work in the kernel (NetBSD) and able to unwind across exception frames s= o you can use kernel debugging and see the stack all the way into the calli= ng process. I haven't found this all that interesting in online debugging,= but it has sometimes been useful in analyzing kernel crash dumps. paul