[lldb-dev] LLDB deadlocks trying to unwind

[Félix Cloutier]

LLDB, connected to a stub I'm building, is trying to produce a stack trace of my stopped program but deadlocks instead:

#0	__psynch_mutexwait ()
#1	pthread_mutex_lock ()
#2	lldb_private::Mutex::Lock() at lldb/source/Host/common/Mutex.cpp:281
#3	lldb_private::Mutex::Locker::Lock(lldb_private::Mutex&) at lldb/source/Host/common/Mutex.cpp:152
#4	lldb_private::Mutex::Locker::Locker(lldb_private::Mutex&) at lldb/source/Host/common/Mutex.cpp:112
#5	lldb_private::Mutex::Locker::Locker(lldb_private::Mutex&) at lldb/source/Host/common/Mutex.cpp:113
#6	lldb_private::Unwind::GetFrameCount() at lldb/include/lldb/Target/Unwind.h:51
#7	UnwindMacOSXFrameBackchain::DoGetFrameInfoAtIndex(unsigned int, unsigned long long&, unsigned long long&) at lldb/source/Plugins/Process/Utility/UnwindMacOSXFrameBackchain.cpp:59
#8	lldb_private::Unwind::GetFrameInfoAtIndex(unsigned int, unsigned long long&, unsigned long long&) at lldb/include/lldb/Target/Unwind.h:78
#9	lldb_private::StackFrameList::GetFramesUpTo(unsigned int) at lldb/source/Target/StackFrameList.cpp:304
#10	lldb_private::StackFrameList::ResetCurrentInlinedDepth() at lldb/source/Target/StackFrameList.cpp:110
#11	lldb_private::StackFrameList::CalculateCurrentInlinedDepth() at lldb/source/Target/StackFrameList.cpp:79
#12	lldb_private::Thread::ShouldStop(lldb_private::Event*) at lldb/source/Target/Thread.cpp:752
#13	lldb_private::ThreadList::ShouldStop(lldb_private::Event*) at lldb/source/Target/ThreadList.cpp:298
#14	lldb_private::Process::ShouldBroadcastEvent(lldb_private::Event*) at lldb/source/Target/Process.cpp:3707
#15	lldb_private::Process::HandlePrivateEvent(std::__1::shared_ptr<lldb_private::Event>&) at lldb/source/Target/Process.cpp:3936
#16	lldb_private::Process::ConnectRemote(lldb_private::Stream*, char const*) at lldb/source/Target/Process.cpp:3257
#17	CommandObjectProcessConnect::DoExecute(lldb_private::Args&, lldb_private::CommandReturnObject&) at lldb/source/Commands/CommandObjectProcess.cpp:1173
#18	lldb_private::CommandObjectParsed::Execute(char const*, lldb_private::CommandReturnObject&) at lldb/source/Interpreter/CommandObject.cpp:1038
#19	lldb_private::CommandInterpreter::HandleCommand(char const*, lldb_private::LazyBool, lldb_private::CommandReturnObject&, lldb_private::ExecutionContext*, bool, bool) at lldb/source/Interpreter/CommandInterpreter.cpp:1825
#20	lldb_private::CommandObjectRegexCommand::DoExecute(char const*, lldb_private::CommandReturnObject&) at lldb/source/Interpreter/CommandObjectRegexCommand.cpp:89
#21	lldb_private::CommandObjectRaw::Execute(char const*, lldb_private::CommandReturnObject&) at lldb/source/Interpreter/CommandObject.cpp:1064
#22	lldb_private::CommandInterpreter::HandleCommand(char const*, lldb_private::LazyBool, lldb_private::CommandReturnObject&, lldb_private::ExecutionContext*, bool, bool) at lldb/source/Interpreter/CommandInterpreter.cpp:1825
#23	lldb::SBCommandInterpreter::HandleCommand(char const*, lldb::SBCommandReturnObject&, bool) at lldb/source/API/SBCommandInterpreter.cpp:122
#24	Driver::HandleIOEvent(lldb::SBEvent const&) at lldb/tools/driver/Driver.cpp:1083
#25	Driver::MainLoop() at lldb/tools/driver/Driver.cpp:1556
#26	main at lldb/tools/driver/Driver.cpp:1727
#27	start ()

#8 locks m_unwind_mutex and #6 tries to do the same thing.

The code path is unconditional (calling GetFrameInfoAtIndex with a UnwindMacOSXFrameBackchain can only end in a deadlock, from what I can see), so I'm not sure how I can prevent this from happening.

Félix
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