Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754327AbdCOVx7 (ORCPT ); Wed, 15 Mar 2017 17:53:59 -0400 Received: from www62.your-server.de ([213.133.104.62]:36411 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754088AbdCOVx4 (ORCPT ); Wed, 15 Mar 2017 17:53:56 -0400 From: Daniel Borkmann To: acme@kernel.org Cc: ast@kernel.org, linux-kernel@vger.kernel.org, Daniel Borkmann Subject: [PATCH] perf: fix symbols__fixup_end heuristic for corner cases Date: Wed, 15 Mar 2017 22:53:37 +0100 Message-Id: X-Mailer: git-send-email 1.9.3 X-Authenticated-Sender: daniel@iogearbox.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2040 Lines: 48 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. 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