Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751147AbdCPBJt (ORCPT ); Wed, 15 Mar 2017 21:09:49 -0400 Received: from mail.kernel.org ([198.145.29.136]:52034 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750865AbdCPBJF (ORCPT ); Wed, 15 Mar 2017 21:09:05 -0400 Date: Wed, 15 Mar 2017 22:07:24 -0300 From: Arnaldo Carvalho de Melo To: Daniel Borkmann Cc: ast@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] perf: fix symbols__fixup_end heuristic for corner cases Message-ID: <20170316010724.GQ12825@kernel.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2284 Lines: 53 Em Wed, Mar 15, 2017 at 10:53:37PM +0100, Daniel Borkmann escreveu: > The current symbols__fixup_end() heuristic for the last entry in the > rb tree is suboptimal as it leads to not being able to recognize the > symbol in the call graph in a couple of corner cases, for example: Thanks, will apply, test and push to Ingo via perf/urgent, tomorrow. - Arnaldo > i) If the symbol has a start address (f.e. exposed via kallsyms) > that is at a page boundary, then the roundup(curr->start, 4096) > for the last entry will result in curr->start == curr->end with > a symbol length of zero. > > ii) If the symbol has a start address that is shortly before a page > boundary, then also here, curr->end - curr->start will just be > very few bytes, where it's unrealistic that we could perform a > match against. > > Instead, change the heuristic to roundup(curr->start, 4096) + 4096, > so that we can catch such corner cases and have a better chance to > find that specific symbol. It's still just best effort as the real > end of the symbol is unknown to us (and could even be at a larger > offset than the current range), but better than the current situation. > > Alexei reported that he recently run into case i) with a JITed eBPF > program (these are all page aligned) as the last symbol which wasn't > properly shown in the call graph (while other eBPF program symbols > in the rb tree were displayed correctly). Since this is a generic > issue, lets try to improve the heuristic a bit. > > Fixes: 2e538c4a1847 ("perf tools: Improve kernel/modules symbol lookup") > Reported-by: Alexei Starovoitov > Signed-off-by: Daniel Borkmann > --- > tools/perf/util/symbol.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c > index 70e389b..9b4d8ba 100644 > --- a/tools/perf/util/symbol.c > +++ b/tools/perf/util/symbol.c > @@ -202,7 +202,7 @@ void symbols__fixup_end(struct rb_root *symbols) > > /* Last entry */ > if (curr->end == curr->start) > - curr->end = roundup(curr->start, 4096); > + curr->end = roundup(curr->start, 4096) + 4096; > } > > void __map_groups__fixup_end(struct map_groups *mg, enum map_type type) > -- > 1.9.3