From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 17840 invoked by alias); 24 Dec 2013 07:54:30 -0000 Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org Received: (qmail 17829 invoked by uid 89); 24 Dec 2013 07:54:28 -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 autolearn=ham version=3.3.2 X-HELO: LGEMRELSE7Q.lge.com Received: from LGEMRELSE7Q.lge.com (HELO LGEMRELSE7Q.lge.com) (156.147.1.151) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 24 Dec 2013 07:54:27 +0000 Received: from sejong.aot.lge.com.lge.com ( [10.177.220.181]) by LGEMRELSE7Q.lge.com (Symantec Brightmail Gateway) with SMTP id 7B.5A.15748.0BD39B25; Tue, 24 Dec 2013 16:54:24 +0900 (KST) From: Namhyung Kim To: Masami Hiramatsu Cc: Arnaldo Carvalho de Melo , Ingo Molnar , Srikar Dronamraju , David Ahern , lkml , "Steven Rostedt \(Red Hat\)" , Oleg Nesterov , "David A. Long" , systemtap@sourceware.org, yrl.pp-manager.tt@hitachi.com Subject: Re: [PATCH -tip 3/3] perf-probe: Use the actual address as a hint for uprobes References: <20131220100255.7169.19384.stgit@kbuild-fedora.novalocal> <20131220100302.7169.96318.stgit@kbuild-fedora.novalocal> <20131220180351.GC28878@ghostprotocols.net> <52B75F9E.7000802@hitachi.com> <87wqiwc8ly.fsf@sejong.aot.lge.com> <52B81562.5000607@hitachi.com> Date: Tue, 24 Dec 2013 07:54:00 -0000 In-Reply-To: <52B81562.5000607@hitachi.com> (Masami Hiramatsu's message of "Mon, 23 Dec 2013 19:50:10 +0900") Message-ID: <87y53afzv3.fsf@sejong.aot.lge.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-SW-Source: 2013-q4/txt/msg00498.txt.bz2 Hi Masami, On Mon, 23 Dec 2013 19:50:10 +0900, Masami Hiramatsu wrote: > (2013/12/23 16:46), Namhyung Kim wrote: >> On Mon, 23 Dec 2013 06:54:38 +0900, Masami Hiramatsu wrote: >>> (2013/12/21 3:03), Arnaldo Carvalho de Melo wrote: >>>> Em Fri, Dec 20, 2013 at 10:03:02AM +0000, Masami Hiramatsu escreveu: >>> BTW, I'm not sure why debuginfo and nm shows symbol address + 0x400000, >>> and why the perf's map/symbol can remove this offset. Could you tell me >>> how it works? >>> If I can get the offset (0x400000) from binary, I don't need this kind >>> of ugly hacks... >> >> AFAIK the actual symbol address is what nm (and debuginfo) shows. But >> perf adjusts symbol address to have a relative address from the start of >> mapping (i.e. file offset) like below: >> >> sym.st_value -= shdr.sh_addr - shdr.sh_offset; > > Thanks! this is what I really need! > >> This way, we can handle mmap and symbol address almost uniformly >> (i.e. ip = map->start + symbol->address). But this requires the mmap >> event during perf record. For perf probe, we might need to synthesize >> mapping info from the section/segment header since it doesn't have the >> mmap event. Currently, the dso__new_map() just creates a map starts >> from 0. > > I think the uprobe requires only the relative address, doesn't that? Yes, but fetching arguments is little different than a normal relative address, I think. An offset of an argument bases on the mapping address of text segment. This fits naturally for a shared library case - base address is 0. So we can use the symbol address (st_value) directly. But for executables, the base address of text segment is 0x400000 on x86-64 and data symbol is on 0x6XXXXX typically. So in this case the offset given to uprobe should be "@+0x2XXXXX" (st_value - text_base). Thanks, Namhyung