linux-kernel - [tip:perf/urgent] perf report: Ensure the perf DSO mapping matches what libdw sees

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Message-ID: <tip-2538b9e2450ae255337c04356e9e0f8cb9ec48d9@git.kernel.org>
Date:   Wed, 7 Jun 2017 09:01:38 -0700
From:   tip-bot for Milian Wolff <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     milian.wolff@...b.com, namhyung@...nel.org, acme@...hat.com,
        mingo@...nel.org, jolsa@...hat.com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, hpa@...or.com
Subject: [tip:perf/urgent] perf report: Ensure the perf DSO mapping matches
 what libdw sees

Commit-ID:  2538b9e2450ae255337c04356e9e0f8cb9ec48d9
Gitweb:     http://git.kernel.org/tip/2538b9e2450ae255337c04356e9e0f8cb9ec48d9
Author:     Milian Wolff <milian.wolff@...b.com>
AuthorDate: Fri, 2 Jun 2017 16:37:52 +0200
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Mon, 5 Jun 2017 14:18:05 -0300

perf report: Ensure the perf DSO mapping matches what libdw sees

In some situations the libdw unwinder stopped working properly.  I.e.
with libunwind we see:

~~~~~
heaptrack_gui  2228 135073.400112:     641314 cycles:
	            e8ed _dl_fixup (/usr/lib/ld-2.25.so)
	           15f06 _dl_runtime_resolve_sse_vex (/usr/lib/ld-2.25.so)
	           ed94c KDynamicJobTracker::KDynamicJobTracker (/home/milian/projects/compiled/kf5/lib64/libKF5KIOWidgets.so.5.35.0)
	           608f3 _GLOBAL__sub_I_kdynamicjobtracker.cpp (/home/milian/projects/compiled/kf5/lib64/libKF5KIOWidgets.so.5.35.0)
	            f199 call_init.part.0 (/usr/lib/ld-2.25.so)
	            f2a5 _dl_init (/usr/lib/ld-2.25.so)
	             db9 _dl_start_user (/usr/lib/ld-2.25.so)
~~~~~

But with libdw and without this patch this sample is not properly
unwound:

~~~~~
heaptrack_gui  2228 135073.400112:     641314 cycles:
	            e8ed _dl_fixup (/usr/lib/ld-2.25.so)
	           15f06 _dl_runtime_resolve_sse_vex (/usr/lib/ld-2.25.so)
	           ed94c KDynamicJobTracker::KDynamicJobTracker (/home/milian/projects/compiled/kf5/lib64/libKF5KIOWidgets.so.5.35.0)
~~~~~

Debug output showed me that libdw found a module for the last frame
address, but it thinks it belongs to /usr/lib/ld-2.25.so. This patch
double-checks what libdw sees and what perf knows. If the mappings
mismatch, we now report the elf known to perf. This fixes the situation
above, and the libdw unwinder produces the same stack as libunwind.

Signed-off-by: Milian Wolff <milian.wolff@...b.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Link: http://lkml.kernel.org/r/20170602143753.16907-1-milian.wolff@kdab.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/unwind-libdw.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index b4c2012..da45c4b 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -39,6 +39,14 @@ static int __report_module(struct addr_location *al, u64 ip,
 		return 0;
 
 	mod = dwfl_addrmodule(ui->dwfl, ip);
+	if (mod) {
+		Dwarf_Addr s;
+
+		dwfl_module_info(mod, NULL, &s, NULL, NULL, NULL, NULL, NULL);
+		if (s != al->map->start)
+			mod = 0;
+	}
+
 	if (!mod)
 		mod = dwfl_report_elf(ui->dwfl, dso->short_name,
 				      dso->long_name, -1, al->map->start,