Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752134AbbF3J7l (ORCPT ); Tue, 30 Jun 2015 05:59:41 -0400 Received: from mga14.intel.com ([192.55.52.115]:26780 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750966AbbF3J7e (ORCPT ); Tue, 30 Jun 2015 05:59:34 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,377,1432623600"; d="scan'208";a="755733513" Message-ID: <559267F0.6@intel.com> Date: Tue, 30 Jun 2015 12:57:04 +0300 From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Will Deacon CC: "acme@redhat.com" , "linux-kernel@vger.kernel.org" , Kristina Martsenko , Vladimir Nikulichev , Namhyung Kim , Andy Lutomirski Subject: Re: [PATCH v2] perf tools: don't adjust symbols in vDSO References: <1435396213-30208-1-git-send-email-will.deacon@arm.com> <55910989.8090608@intel.com> <55913A57.2000602@intel.com> <559146E7.1070201@intel.com> <20150629135238.GC17474@arm.com> In-Reply-To: <20150629135238.GC17474@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1901 Lines: 51 On 29/06/15 16:52, Will Deacon wrote: > On Mon, Jun 29, 2015 at 02:23:51PM +0100, Adrian Hunter wrote: >> On 29/06/15 15:30, Adrian Hunter wrote: >>> On 29/06/15 12:02, Adrian Hunter wrote: >>>> On 27/06/15 12:10, Will Deacon wrote: >>>>> @@ -824,6 +823,14 @@ int dso__load_sym(struct dso *dso, struct map *map, >>>>> sec = syms_ss->symtab; >>>>> shdr = syms_ss->symshdr; >>>>> >>>>> + /* >>>>> + * Older x86 kernels prelink the vDSO at a high address, so >>>>> + * we need to reflect that in map->pgoff in order to talk to >>>>> + * objdump. >>>>> + */ >>>>> + if (dso__is_vdso(dso)) >>>>> + map->pgoff = shdr.sh_addr - shdr.sh_offset; >>>> >>>> In the case of perf tools, maps map memory addresses to file offsets. >>>> That is used to read from the object file, so you can't change the map. >>> >>> So what about just this instead: >>> >>> if (dso__is_vdso(dso)) >>> map->reloc = shdr.sh_addr - shdr.sh_offset; >>> >> >> No that's no good either :-( > > Yeah... we're fighting against symbol lookup wanting ->map_ip to give the > address of the ELF symbol but unwinding wanting ->map_ip to give a relative > offset for file reads. > > Also, the reloc is a bit weird and I think needs to be the other way around > (i.e. we convert from a map-relative address to an objdump address by > *subtracting* the reloc). Even with that change, I run into problems with > annotate comparing ELF symbol addresses with map addresses. Urgh. Adding or subtracting shouldn't matter. This seems to work (without any other changes): if (dso__is_vdso(dso)) map->reloc = map->start - shdr.sh_addr + shdr.sh_offset; Haven't tested 32-bit yet though. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/