Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751949AbbF2Nwv (ORCPT ); Mon, 29 Jun 2015 09:52:51 -0400 Received: from foss.arm.com ([217.140.101.70]:38187 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753266AbbF2Nwn (ORCPT ); Mon, 29 Jun 2015 09:52:43 -0400 Date: Mon, 29 Jun 2015 14:52:39 +0100 From: Will Deacon To: Adrian Hunter 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 Message-ID: <20150629135238.GC17474@arm.com> References: <1435396213-30208-1-git-send-email-will.deacon@arm.com> <55910989.8090608@intel.com> <55913A57.2000602@intel.com> <559146E7.1070201@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <559146E7.1070201@intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1640 Lines: 42 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. Will -- 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/