perf unwind: Report module before querying isactivation in dwfl unwind

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.

Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Acked-by: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20170602143753.16907-2-milian.wolff@kdab.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index da45c4be5fb3e77ee59131602667b4d675bc3a40..7755a5e0fe5eb290c41502bf22725cce8a0b6935 100644 (file)
--- 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;