Re: [PATCH 2/2] perf report: report module before querying isactivation in dwfl unwind

From: Arnaldo Carvalho de Melo
Date: Fri Jun 16 2017 - 12:07:09 EST

Em Fri, Jun 02, 2017 at 12:25:08PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Jun 02, 2017 at 04:37:53PM +0200, Milian Wolff escreveu:
> > 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.:
>
> Jiri, can you review this one?

ping

> Thanks,
>
> - Arnaldo
>
> > ~~~~~
> > 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@xxxxxxxxxx>
> > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Signed-off-by: Milian Wolff <milian.wolff@xxxxxxxx>
> > ---
> > 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
> --
> To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html