From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759984Ab2FUR3I (ORCPT ); Thu, 21 Jun 2012 13:29:08 -0400 Received: from mail-yx0-f174.google.com ([209.85.213.174]:38462 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755032Ab2FUR3G (ORCPT ); Thu, 21 Jun 2012 13:29:06 -0400 Date: Thu, 21 Jun 2012 14:28:59 -0300 From: Arnaldo Carvalho de Melo To: "Pierre-Loup A. Griffais" Cc: linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, paulus@samba.org, mingo@redhat.com, torvalds@linux-foundation.org, Mike Sartain Subject: Re: [PATCH] perf symbols: Follow .gnu_debuglink section to find separate symbols Message-ID: <20120621172859.GA17747@infradead.org> References: <4FE24D31.3070608@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FE24D31.3070608@nvidia.com> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Wed, Jun 20, 2012 at 03:22:41PM -0700, Pierre-Loup A. Griffais escreveu: > The .gnu_debuglink section is specified to contain the filename of the > debug info file, as well as a CRC that can be used to validate it. > This provides more context: > http://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html > > +++ b/tools/perf/util/symbol.c > +static int filename__read_debuglink(const char *filename, > + char *path, size_t size) > +{ Isn't there any other function that opens an ELF file, looks for an specific session to then read its contents? Couldn't it be reused here? > + case SYMTAB__DEBUGLINK: { > + char *last_slash; > + strncpy(name, dso->long_name, size); > + last_slash = name + dso->long_name_len; > + while (last_slash && *last_slash != '/') > + last_slash--; Why the test for last_slash to be != NULL? How could it ever be? This is an optimization since we have the dso->long_name_len so that we avoid using strrchr that in turn would do an strlen? So the test should be: while (last_slash != name && *last_slash != '/') To avoid underflowing, right? > + if (last_slash) > + last_slash++; > + filename__read_debuglink(dso->long_name, last_slash, How last_slash can point to the path? It looks like it points to the basename, no? Yeah, it is, and then your algorithm will work because last_slash doesn't point to the _path_, but to a string _preceded_ by the path, so for /bin/ls, the debuglink content would be ls.debug and that is what will be stashed there, ending up with: name = "/bin/\0" last_slash---^ name = "/bin/ls.debug\0" I.e. its not really the last slash, but where the debuglink content has to be stashed, concatenating with the same dirname as the associated binary. Can you please rename "last_slash" to "debuglink"? And "path" to "debuglink" as well in the routine that reads the debuglink. > + size - (last_slash - name)); > + } Other than that, thanks a lot for working on this, surely we have to support this feature! - ARnaldo