Crash on debugging a segfaulted rr trace

tinloaf commented 10 months ago

With the recent main, my seergdb crashes when I try to debug a segfault that I recorded via rr. I am using rr version 5.7.0.

Note: I can only reproduce this when debugging an rr trace, not when 'directly' debugging using seergdb. I don't think that this is really dependent on rr, but I suspect the crucial fact is that in rr mode, seergdb already stops once before main() and the 'Locals' tab is populated. If I don't open the 'Locals' tab at this point (see step 5 below), the crash disappears.

Reproduction

I can reproduce it like this:

Create a segfaulting file, e.g. this mnwe.cpp file:

int main() {
int * i = nullptr;
*i = 42;

return 0;
}

Compile as g++ -g -O0 mnwe.cpp -o mnwe
Record the trace using rr: rr record --output-trace-dir=rrrun ./mnwe (you should see the segfault)
Start seergdb with this trace: seergdb --rr rrrun
When seergbd stops before main(), make sure that the 'Locals' tab is open
Hit F8 to run the trace

At this point, my seergbd crashes.

Backtrace

This is the backtrace I see when running the above under gdb:

Thread 1 "seergdb" received signal SIGSEGV, Segmentation fault.
0x00005555556eadcc in qDeleteAll<QList<QTreeWidgetItem*>::const_iterator> (begin=..., end=...)
    at /usr/include/x86_64-linux-gnu/qt6/QtCore/qalgorithms.h:23
23              delete *begin;
(gdb) bt
#0  0x00005555556eadcc in qDeleteAll<QList<QTreeWidgetItem*>::const_iterator> (begin=..., end=...)
    at /usr/include/x86_64-linux-gnu/qt6/QtCore/qalgorithms.h:23
#1  0x00005555556eabef in qDeleteAll<QList<QTreeWidgetItem*> > (c=...) at /usr/include/x86_64-linux-gnu/qt6/QtCore/qalgorithms.h:31
#2  0x000055555581568f in SeerStackLocalsBrowserWidget::handleText (this=0x555555d5bad0, text=...)
    at ~/src/seer/src/SeerStackLocalsBrowserWidget.cpp:89
#3  0x00005555557a05ff in QtPrivate::FunctorCall<QtPrivate::IndexesList<0>, QtPrivate::List<QString const&>, void, void (SeerStackLocalsBrowserWidget::*)(QString const&)>::call (
    f=(void (SeerStackLocalsBrowserWidget::*)(SeerStackLocalsBrowserWidget * const, const QString &)) 0x55555581511a <SeerStackLocalsBrowserWidget::handleText(QString const&)>, o=0x555555d5bad0, arg=0x7fffffffd0e0) at /usr/include/x86_64-linux-gnu/qt6/QtCore/qobjectdefs_impl.h:135
#4  0x000055555579ecbd in QtPrivate::FunctionPointer<void (SeerStackLocalsBrowserWidget::*)(QString const&)>::call<QtPrivate::List<QString const&>, void> (
    f=(void (SeerStackLocalsBrowserWidget::*)(SeerStackLocalsBrowserWidget * const, const QString &)) 0x55555581511a <SeerStackLocalsBrowserWidget::handleText(QString const&)>, o=0x555555d5bad0, arg=0x7fffffffd0e0) at /usr/include/x86_64-linux-gnu/qt6/QtCore/qobjectdefs_impl.h:172
#5  0x000055555579b8df in QtPrivate::QSlotObject<void (SeerStackLocalsBrowserWidget::*)(QString const&), QtPrivate::List<QString const&>, void>::impl
    (which=1, this_=0x555555d9e370, r=0x555555d5bad0, a=0x7fffffffd0e0, ret=0x0) at /usr/include/x86_64-linux-gnu/qt6/QtCore/qobjectdefs_impl.h:383
#6  0x00007ffff6b11326 in ?? () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#7  0x00005555556a2830 in GdbMonitor::caretTextOutput (this=0x555555b53b70, _t1=...)
    at ~/src/seer/src/build/seergdb_autogen/EWIEGA46WW/moc_GdbMonitor.cpp:371
#8  0x00005555556d1c50 in GdbMonitor::handleReadyReadStandardOutput (this=0x555555b53b70) at ~/src/seer/src/GdbMonitor.cpp:98
#9  0x000055555579fcb6 in QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, void (GdbMonitor::*)()>::call(void (GdbMonitor::*)(), GdbMonitor*, void**) (f=(void (GdbMonitor::*)(GdbMonitor * const)) 0x5555556d18f0 <GdbMonitor::handleReadyReadStandardOutput()>,
    o=0x555555b53b70, arg=0x7fffffffd370) at /usr/include/x86_64-linux-gnu/qt6/QtCore/qobjectdefs_impl.h:135
#10 0x000055555579e951 in QtPrivate::FunctionPointer<void (GdbMonitor::*)()>::call<QtPrivate::List<>, void>(void (GdbMonitor::*)(), GdbMonitor*, void**) (f=(void (GdbMonitor::*)(GdbMonitor * const)) 0x5555556d18f0 <GdbMonitor::handleReadyReadStandardOutput()>, o=0x555555b53b70, arg=0x7fffffffd370)
    at /usr/include/x86_64-linux-gnu/qt6/QtCore/qobjectdefs_impl.h:172
#11 0x000055555579ad57 in QtPrivate::QSlotObject<void (GdbMonitor::*)(), QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) (which=1, this_=0x555555b6b640, r=0x555555b53b70, a=0x7fffffffd370, ret=0x0)
    at /usr/include/x86_64-linux-gnu/qt6/QtCore/qobjectdefs_impl.h:383
#12 0x00007ffff6b11326 in ?? () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#13 0x00007ffff6c4e021 in QProcess::readyReadStandardOutput(QProcess::QPrivateSignal) () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#14 0x00007ffff6c4e2dd in ?? () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#15 0x00007ffff6c51515 in ?? () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#16 0x00007ffff6b116d3 in ?? () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#17 0x00007ffff6b155d3 in QSocketNotifier::activated(QSocketDescriptor, QSocketNotifier::Type, QSocketNotifier::QPrivateSignal) ()
   from /lib/x86_64-linux-gnu/libQt6Core.so.6
#18 0x00007ffff6b17bd3 in QSocketNotifier::event(QEvent*) () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#19 0x00007ffff775daab in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /lib/x86_64-linux-gnu/libQt6Widgets.so.6
#20 0x00007ffff6ac6858 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#21 0x00007ffff6cbc58f in ?? () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#22 0x00007ffff60e749d in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#23 0x00007ffff6142178 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#24 0x00007ffff60e61b0 in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#25 0x00007ffff6cb3f20 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#26 0x00007ffff6ad09aa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#27 0x00007ffff6ac971c in QCoreApplication::exec() () from /lib/x86_64-linux-gnu/libQt6Core.so.6
#28 0x00005555556cd226 in main (argc=3, argv=0x7fffffffdf48) at ~/src/seer/src/seergdb.cpp:338

epasveer commented 10 months ago

Thanks for the detailed problem report. I should be able to reproduce it using your directions.

epasveer commented 9 months ago

I wasn't able to duplicate it with your instructions. However, the traceback pointed me to the error in my code.

I've fixed it in the mainline.

tinloaf commented 9 months ago

The crash is gone, thanks a lot!

epasveer / seer

Crash on debugging a segfaulted rr trace #181

Reproduction

Backtrace