[Lldb-commits] [PATCH] D74398: [lldb-server] jThreadsInfo returns stack memory

Tue Mar 31 02:10:27 PDT 2020

jarin added a comment.

In D74398#1939372 <https://reviews.llvm.org/D74398#1939372>, @jarin wrote:

> In D74398#1935438 <https://reviews.llvm.org/D74398#1935438>, @jasonmolenda wrote:
>
> > (and if you're still seeing mystery reads, put a breakpoint on ProcessGDBRemote::DoReadMemory and see who is doing it)
>
>
> Thanks for the great explanations! I did put a breakpoint into DoReadMemory, and the unwinder doing the reads for each thread (called from https://github.com/llvm/llvm-project/blob/master/lldb/source/Target/ThreadList.cpp#L349). If I understand correctly, the Thread::WillStop/SelectMostRelevantFrame should care only about the current PC of each thread, but not about the stack contents. Let me double check that.

Looking at this in more detail, Thread::WillStop will unwind more than one frame (for each thread), the stack trace is below. I guess the surprising bit is that UnwindLLDB::UpdateUnwindPlanForFirstFrameIfInvalid (frame #11) always unwinds one more frame. Is that expected?

#0: process_gdb_remote::ProcessGDBRemote::DoReadMemory() at ProcessGDBRemote.cpp:2694:54
#1: Process::ReadMemoryFromInferior() at Process.cpp:2092:21
#2: Process::ReadMemoryFromInferior() at Process.cpp:2081
#3: MemoryCache::Read() at Memory.cpp:229:69
#4: RegisterContext::ReadRegisterValueFromMemory() at RegisterContext.cpp:337:31
#5: RegisterContextUnwind::ReadRegisterValueFromRegisterLocation() at RegisterContextUnwind.cpp:1040:15
#6: RegisterContextUnwind::ReadGPRValue() at RegisterContextUnwind.cpp:2008:44
#7: RegisterContextUnwind::InitializeNonZerothFrame() at RegisterContextUnwind.cpp:287:20
#8: RegisterContextUnwind::RegisterContextUnwind() at RegisterContextUnwind.cpp:70:29
#9: UnwindLLDB::GetOneMoreFrame() at UnwindLLDB.cpp:129:77
#10: UnwindLLDB::AddOneMoreFrame() at UnwindLLDB.cpp:332:32
#11: UnwindLLDB::UpdateUnwindPlanForFirstFrameIfInvalid() at UnwindLLDB.cpp:305:18
#12: UnwindLLDB::AddFirstFrame() at UnwindLLDB.cpp:99:41
#13: UnwindLLDB::AddFirstFrame() at UnwindLLDB.cpp:70
#14: UnwindLLDB::DoGetFrameInfoAtIndex() at UnwindLLDB.cpp:395:23
#15: StackFrameList::GetFramesUpTo() at Unwind.h:53:33
#16: StackFrameList::GetFrameAtIndex() at StackFrameList.cpp:660:16
#17: Thread::SelectMostRelevantFrame() at Thread.cpp:612:52
#18: Thread::WillStop() at Thread.cpp:634:26
#19: ThreadList::ShouldStop() at ThreadList.cpp:349:26
#20: Process::ShouldBroadcastEvent() at Process.cpp:3427:50
#21: Process::HandlePrivateEvent() at Process.cpp:3652:53
#22: Process::RunPrivateStateThread() at Process.cpp:3846:25

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