tberghammer created this revision.
tberghammer added a reviewer: jasonmolenda.
tberghammer added a subscriber: lldb-commits.
Change the looping stack detection code
In some special case (e.g. signal handlers, hand written assembly) it is
valid to have 2 stack frame with the same CFA value. This CL change the
looping stack detection code to report a loop only if at least 3
consecutive frames have the same CFA.
Note: I would prefer to get rid of this looping stack detection because the
implementation is still a bit flaky and rely on the logic in
UnwindLLDB::GetOneMoreFrame to stop the infinite loop in case of a looping
stack, but I don't know how big the user impact will be in the cases where the
unwind go wrong and start looping
http://reviews.llvm.org/D12699
Files:
source/Plugins/Process/Utility/RegisterContextLLDB.cpp
Index: source/Plugins/Process/Utility/RegisterContextLLDB.cpp
===================================================================
--- source/Plugins/Process/Utility/RegisterContextLLDB.cpp
+++ source/Plugins/Process/Utility/RegisterContextLLDB.cpp
@@ -634,28 +634,30 @@
RegisterContextLLDB::CheckIfLoopingStack ()
{
// If we have a bad stack setup, we can get the same CFA value multiple
times -- or even
- // more devious, we can actually oscillate between two CFA values. Detect
that here and
+ // more devious, we can actually oscillate between two CFA values. Detect
that here and
// break out to avoid a possible infinite loop in lldb trying to unwind
the stack.
- addr_t next_frame_cfa;
- addr_t next_next_frame_cfa = LLDB_INVALID_ADDRESS;
- if (GetNextFrame().get() && GetNextFrame()->GetCFA(next_frame_cfa))
+ // To detect when we have the same CFA value multiple times, we compare
the CFA of the current
+ // frame with the 2nd next frame because in some specail case (e.g. signal
hanlders, hand
+ // written assembly without ABI compiance) we can have 2 frames with the
same CFA (in theory we
+ // can have arbitrary number of frames with the same CFA, but more then 2
is very very unlikely)
+
+ RegisterContextLLDB::SharedPtr next_frame = GetNextFrame();
+ if (next_frame)
{
- if (next_frame_cfa == m_cfa)
- {
- // We have a loop in the stack unwind
- return true;
- }
- if (GetNextFrame()->GetNextFrame().get() &&
GetNextFrame()->GetNextFrame()->GetCFA(next_next_frame_cfa)
- && next_next_frame_cfa == m_cfa)
+ RegisterContextLLDB::SharedPtr next_next_frame =
next_frame->GetNextFrame();
+ addr_t next_next_frame_cfa = LLDB_INVALID_ADDRESS;
+ if (next_next_frame && next_next_frame->GetCFA(next_next_frame_cfa))
{
- // We have a loop in the stack unwind
- return true;
+ if (next_next_frame_cfa == m_cfa)
+ {
+ // We have a loop in the stack unwind
+ return true;
+ }
}
}
return false;
}
-
bool
RegisterContextLLDB::IsFrameZero () const
{
Index: source/Plugins/Process/Utility/RegisterContextLLDB.cpp
===================================================================
--- source/Plugins/Process/Utility/RegisterContextLLDB.cpp
+++ source/Plugins/Process/Utility/RegisterContextLLDB.cpp
@@ -634,28 +634,30 @@
RegisterContextLLDB::CheckIfLoopingStack ()
{
// If we have a bad stack setup, we can get the same CFA value multiple times -- or even
- // more devious, we can actually oscillate between two CFA values. Detect that here and
+ // more devious, we can actually oscillate between two CFA values. Detect that here and
// break out to avoid a possible infinite loop in lldb trying to unwind the stack.
- addr_t next_frame_cfa;
- addr_t next_next_frame_cfa = LLDB_INVALID_ADDRESS;
- if (GetNextFrame().get() && GetNextFrame()->GetCFA(next_frame_cfa))
+ // To detect when we have the same CFA value multiple times, we compare the CFA of the current
+ // frame with the 2nd next frame because in some specail case (e.g. signal hanlders, hand
+ // written assembly without ABI compiance) we can have 2 frames with the same CFA (in theory we
+ // can have arbitrary number of frames with the same CFA, but more then 2 is very very unlikely)
+
+ RegisterContextLLDB::SharedPtr next_frame = GetNextFrame();
+ if (next_frame)
{
- if (next_frame_cfa == m_cfa)
- {
- // We have a loop in the stack unwind
- return true;
- }
- if (GetNextFrame()->GetNextFrame().get() && GetNextFrame()->GetNextFrame()->GetCFA(next_next_frame_cfa)
- && next_next_frame_cfa == m_cfa)
+ RegisterContextLLDB::SharedPtr next_next_frame = next_frame->GetNextFrame();
+ addr_t next_next_frame_cfa = LLDB_INVALID_ADDRESS;
+ if (next_next_frame && next_next_frame->GetCFA(next_next_frame_cfa))
{
- // We have a loop in the stack unwind
- return true;
+ if (next_next_frame_cfa == m_cfa)
+ {
+ // We have a loop in the stack unwind
+ return true;
+ }
}
}
return false;
}
-
bool
RegisterContextLLDB::IsFrameZero () const
{
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