Re: [PATCH 2/2] perf report: report module before querying isactivation in dwfl unwind
From: Arnaldo Carvalho de Melo
Date: Fri Jun 02 2017 - 11:25:17 EST
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?
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