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From: Milian Wolff <milian.wolff@kdab.com>
To: Linux-kernel@vger.kernel.org
Cc: linux-perf-users@vger.kernel.org,
	Milian Wolff <milian.wolff@kdab.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>, Jiri Olsa <jolsa@redhat.com>
Subject: [PATCH 2/2] perf report: report module before querying isactivation in dwfl unwind
Date: Fri,  2 Jun 2017 16:37:53 +0200
Message-ID: <20170602143753.16907-2-milian.wolff@kdab.com> (raw)
In-Reply-To: <20170602143753.16907-1-milian.wolff@kdab.com>

The PC returned by dwfl_frame_pc may map into a not-yet-reported
module. We have to report it before we continue unwinding. But when
we query for the isactivation flag in dwfl_frame_pc, libdw will
actually do one more unwinding step internally which can then break
and lead to missed frames or broken stacks.

With libunwind we get e.g.:

~~~~~
heaptrack_gui  2228 135073.400474:     613969 cycles:
	          108c8e [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          1093bc [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          109e7b QLocale::QLocale (/usr/lib/libQt5Core.so.5.8.0)
	          1470ff [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          147f67 QSystemLocale::query (/usr/lib/libQt5Core.so.5.8.0)
	          109fbf QLocalePrivate::updateSystemPrivate (/usr/lib/libQt5Core.so.5.8.0)
	          10aa27 QLocale::QLocale (/usr/lib/libQt5Core.so.5.8.0)
	          1e02c3 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          2113bb [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          211505 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          1b5df0 QFileInfo::exists (/usr/lib/libQt5Core.so.5.8.0)
	           92eb2 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	           93423 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	           93d2a QLibraryInfo::location (/usr/lib/libQt5Core.so.5.8.0)
	          2170af [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          297c53 QCoreApplicationPrivate::init (/usr/lib/libQt5Core.so.5.8.0)
	           f7cde QGuiApplicationPrivate::init (/usr/lib/libQt5Gui.so.5.8.0)
	          1589e8 QApplicationPrivate::init (/usr/lib/libQt5Widgets.so.5.8.0)
	           78622 main (/home/milian/projects/compiled/other/bin/heaptrack_gui)
	           20439 __libc_start_main (/usr/lib/libc-2.25.so)
	           78299 _start (/home/milian/projects/compiled/other/bin/heaptrack_gui)

heaptrack_gui  2228 135073.401156:     569521 cycles:
	          131633 QString::endsWith (/usr/lib/libQt5Core.so.5.8.0)
	          1a0701 QDir::cleanPath (/usr/lib/libQt5Core.so.5.8.0)
	          21b82d [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          1b3727 QFileInfo::canonicalFilePath (/usr/lib/libQt5Core.so.5.8.0)
	          2780c7 QFactoryLoader::update (/usr/lib/libQt5Core.so.5.8.0)
	          279525 QFactoryLoader::QFactoryLoader (/usr/lib/libQt5Core.so.5.8.0)
	           e5bd0 QPlatformIntegrationFactory::create (/usr/lib/libQt5Gui.so.5.8.0)
	           f5a1c QGuiApplicationPrivate::createPlatformIntegration (/usr/lib/libQt5Gui.so.5.8.0)
	           f650c QGuiApplicationPrivate::createEventDispatcher (/usr/lib/libQt5Gui.so.5.8.0)
	          298524 QCoreApplicationPrivate::init (/usr/lib/libQt5Core.so.5.8.0)
	           f7cde QGuiApplicationPrivate::init (/usr/lib/libQt5Gui.so.5.8.0)
	          1589e8 QApplicationPrivate::init (/usr/lib/libQt5Widgets.so.5.8.0)
	           78622 main (/home/milian/projects/compiled/other/bin/heaptrack_gui)
	           20439 __libc_start_main (/usr/lib/libc-2.25.so)
	           78299 _start (/home/milian/projects/compiled/other/bin/heaptrack_gui)
~~~~~

Note the two frames 1589e8 and 78622 in the first sample. These are
missing when unwinding with libdw. The second sample's breakage is
more obvious:

~~~~~
heaptrack_gui  2228 135073.400474:     613969 cycles:
	          108c8e [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          1093bc [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          109e7b QLocale::QLocale (/usr/lib/libQt5Core.so.5.8.0)
	          1470ff [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          147f67 QSystemLocale::query (/usr/lib/libQt5Core.so.5.8.0)
	          109fbf QLocalePrivate::updateSystemPrivate (/usr/lib/libQt5Core.so.5.8.0)
	          10aa27 QLocale::QLocale (/usr/lib/libQt5Core.so.5.8.0)
	          1e02c3 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          2113bb [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          211505 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          1b5df0 QFileInfo::exists (/usr/lib/libQt5Core.so.5.8.0)
	           92eb2 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	           93423 [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	           93d2a QLibraryInfo::location (/usr/lib/libQt5Core.so.5.8.0)
	          2170af [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          297c53 QCoreApplicationPrivate::init (/usr/lib/libQt5Core.so.5.8.0)
	           f7cde QGuiApplicationPrivate::init (/usr/lib/libQt5Gui.so.5.8.0)
	           20439 __libc_start_main (/usr/lib/libc-2.25.so)
	           78299 _start (/home/milian/projects/compiled/other/bin/heaptrack_gui)

heaptrack_gui  2228 135073.401156:     569521 cycles:
	          131633 QString::endsWith (/usr/lib/libQt5Core.so.5.8.0)
	          1a0701 QDir::cleanPath (/usr/lib/libQt5Core.so.5.8.0)
	          21b82d [unknown] (/usr/lib/libQt5Core.so.5.8.0)
	          1b3727 QFileInfo::canonicalFilePath (/usr/lib/libQt5Core.so.5.8.0)
	          2780c7 QFactoryLoader::update (/usr/lib/libQt5Core.so.5.8.0)
	          279525 QFactoryLoader::QFactoryLoader (/usr/lib/libQt5Core.so.5.8.0)
	           e5bd0 QPlatformIntegrationFactory::create (/usr/lib/libQt5Gui.so.5.8.0)
	          723dbf [unknown] ([unknown])
~~~~~

This patch fixes this issue and the libdw unwinder mimicks the
libunwind behavior more closely.

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Milian Wolff <milian.wolff@kdab.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 da45c4be5fb3..7755a5e0fe5e 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -178,6 +178,14 @@ frame_callback(Dwfl_Frame *state, void *arg)
 	Dwarf_Addr pc;
 	bool isactivation;
 
+	if (!dwfl_frame_pc(state, &pc, NULL)) {
+		pr_err("%s", dwfl_errmsg(-1));
+		return DWARF_CB_ABORT;
+	}
+
+	// report the module before we query for isactivation
+	report_module(pc, ui);
+
 	if (!dwfl_frame_pc(state, &pc, &isactivation)) {
 		pr_err("%s", dwfl_errmsg(-1));
 		return DWARF_CB_ABORT;
-- 
2.13.0

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-02 14:37 [PATCH 1/2] perf report: ensure the perf DSO mapping matches what libdw sees Milian Wolff
2017-06-02 14:37 ` Milian Wolff [this message]
2017-06-02 15:25   ` [PATCH 2/2] perf report: report module before querying isactivation in dwfl unwind Arnaldo Carvalho de Melo
2017-06-05 10:47     ` Jiri Olsa
2017-06-15 19:20       ` Jan Kratochvil
2017-06-16 16:06     ` Arnaldo Carvalho de Melo
2017-06-16 17:36       ` Arnaldo Carvalho de Melo
2017-06-02 15:23 ` [PATCH 1/2] perf report: ensure the perf DSO mapping matches what libdw sees Arnaldo Carvalho de Melo
2017-06-02 16:21   ` Milian Wolff
2017-06-02 19:49     ` Arnaldo Carvalho de Melo
2017-06-03 11:36       ` Milian Wolff
2017-06-05 10:41 ` Jiri Olsa
2017-06-15 20:38   ` Jan Kratochvil

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