Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753345AbdGPO1p (ORCPT ); Sun, 16 Jul 2017 10:27:45 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:44258 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753262AbdGPOPX (ORCPT ); Sun, 16 Jul 2017 10:15:23 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Arnaldo Carvalho de Melo" , "Daniel Borkmann" Date: Sun, 16 Jul 2017 14:56:46 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 068/178] perf symbols: Fix symbols__fixup_end heuristic for corner cases In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2358 Lines: 55 3.16.46-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Borkmann commit e7ede72a6d40cb3a30c087142d79381ca8a31dab upstream. 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: 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. Reported-and-Tested-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Fixes: 2e538c4a1847 ("perf tools: Improve kernel/modules symbol lookup") Link: http://lkml.kernel.org/r/bb5c80d27743be6f12afc68405f1956a330e1bc9.1489614365.git.daniel@iogearbox.net Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: Ben Hutchings --- tools/perf/util/symbol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -188,7 +188,7 @@ void symbols__fixup_end(struct rb_root * /* 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)