[Lldb-commits] [lldb] r241434 - Improve UnwindLLDB with better detection for unwinding failures
Tamas Berghammer
tberghammer at google.com
Mon Jul 6 02:24:21 PDT 2015
Author: tberghammer
Date: Mon Jul 6 04:24:20 2015
New Revision: 241434
URL: http://llvm.org/viewvc/llvm-project?rev=241434&view=rev
Log:
Improve UnwindLLDB with better detection for unwinding failures
Previously we accepted a frame as correct result if the PC pointed
into an executable section of code. The isse with that approac is
that if we calculated PC correctly but messed up the value of CFA
then unwinding from the next fram will most likely fail.
With this change I modify the logic with keeping the requirement
for PC to point to an executable section and also check that we can
continue the unwind from the frame we calculated. If continuing from
the frame calculated with the primary unwind plan isn't working then
fall back to the fallback plan with the hope for a better frame (if
the fallback plan won't help then we acceot the frame from the
primary plan).
Differential revision: http://reviews.llvm.org/D10932
Modified:
lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.cpp
lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.h
Modified: lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.cpp
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.cpp?rev=241434&r1=241433&r2=241434&view=diff
==============================================================================
--- lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.cpp (original)
+++ lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.cpp Mon Jul 6 04:24:20 2015
@@ -120,29 +120,28 @@ unwind_done:
return false;
}
-// For adding a non-zero stack frame to m_frames.
-bool
-UnwindLLDB::AddOneMoreFrame (ABI *abi)
+UnwindLLDB::CursorSP
+UnwindLLDB::GetOneMoreFrame (ABI* abi)
{
+ assert (m_frames.size() != 0 && "Get one more frame called with empty frame list");
+
// If we've already gotten to the end of the stack, don't bother to try again...
if (m_unwind_complete)
- return false;
+ return nullptr;
Log *log(GetLogIfAllCategoriesSet (LIBLLDB_LOG_UNWIND));
- CursorSP cursor_sp(new Cursor ());
- // Frame zero is a little different
- if (m_frames.size() == 0)
- return false;
+ CursorSP prev_frame = m_frames.back();
+ uint32_t cur_idx = m_frames.size();
- uint32_t cur_idx = m_frames.size ();
+ CursorSP cursor_sp(new Cursor ());
RegisterContextLLDBSP reg_ctx_sp(new RegisterContextLLDB (m_thread,
- m_frames[cur_idx - 1]->reg_ctx_lldb_sp,
+ prev_frame->reg_ctx_lldb_sp,
cursor_sp->sctx,
cur_idx,
*this));
- // We want to detect an unwind that cycles erronously and stop backtracing.
+ // We want to detect an unwind that cycles erroneously and stop backtracing.
// Don't want this maximum unwind limit to be too low -- if you have a backtrace
// with an "infinitely recursing" bug, it will crash when the stack blows out
// and the first 35,000 frames are uninteresting - it's the top most 5 frames that
@@ -154,21 +153,20 @@ UnwindLLDB::AddOneMoreFrame (ABI *abi)
if (log)
log->Printf ("%*sFrame %d unwound too many frames, assuming unwind has gone astray, stopping.",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- goto unwind_done;
+ return nullptr;
}
if (reg_ctx_sp.get() == NULL)
{
// If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
// true. Subsequent calls to TryFallbackUnwindPlan() will return false.
- if (m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
- {
- return AddOneMoreFrame (abi);
- }
+ if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+ return GetOneMoreFrame (abi);
+
if (log)
log->Printf ("%*sFrame %d did not get a RegisterContext, stopping.",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- goto unwind_done;
+ return nullptr;
}
if (!reg_ctx_sp->IsValid())
@@ -176,31 +174,25 @@ UnwindLLDB::AddOneMoreFrame (ABI *abi)
// We failed to get a valid RegisterContext.
// See if the regctx below this on the stack has a fallback unwind plan it can use.
// Subsequent calls to TryFallbackUnwindPlan() will return false.
- if (m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
- {
- return AddOneMoreFrame (abi);
- }
+ if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+ return GetOneMoreFrame (abi);
+
if (log)
- {
log->Printf("%*sFrame %d invalid RegisterContext for this frame, stopping stack walk",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- }
- goto unwind_done;
+ return nullptr;
}
if (!reg_ctx_sp->GetCFA (cursor_sp->cfa))
{
// If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
// true. Subsequent calls to TryFallbackUnwindPlan() will return false.
- if (m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
- {
- return AddOneMoreFrame (abi);
- }
+ if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+ return GetOneMoreFrame (abi);
+
if (log)
- {
log->Printf("%*sFrame %d did not get CFA for this frame, stopping stack walk",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- }
- goto unwind_done;
+ return nullptr;
}
if (abi && !abi->CallFrameAddressIsValid(cursor_sp->cfa))
{
@@ -219,24 +211,19 @@ UnwindLLDB::AddOneMoreFrame (ABI *abi)
|| reg_ctx_sp->GetCFA (cursor_sp->cfa) == false
|| abi->CallFrameAddressIsValid(cursor_sp->cfa) == false)
{
- if (m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
- {
- return AddOneMoreFrame (abi);
- }
+ if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+ return GetOneMoreFrame (abi);
+
if (log)
- {
log->Printf("%*sFrame %d did not get a valid CFA for this frame, stopping stack walk",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- }
- goto unwind_done;
+ return nullptr;
}
else
{
if (log)
- {
log->Printf("%*sFrame %d had a bad CFA value but we switched the UnwindPlan being used and got one that looks more realistic.",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- }
}
}
}
@@ -244,54 +231,103 @@ UnwindLLDB::AddOneMoreFrame (ABI *abi)
{
// If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
// true. Subsequent calls to TryFallbackUnwindPlan() will return false.
- if (m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
- {
- return AddOneMoreFrame (abi);
- }
+ if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+ return GetOneMoreFrame (abi);
+
if (log)
- {
log->Printf("%*sFrame %d did not get PC for this frame, stopping stack walk",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- }
- goto unwind_done;
+ return nullptr;
}
if (abi && !abi->CodeAddressIsValid (cursor_sp->start_pc))
{
// If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
// true. Subsequent calls to TryFallbackUnwindPlan() will return false.
- if (m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
- {
- return AddOneMoreFrame (abi);
- }
+ if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+ return GetOneMoreFrame (abi);
+
if (log)
- {
log->Printf("%*sFrame %d did not get a valid PC, stopping stack walk",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
- }
- goto unwind_done;
+ return nullptr;
}
- if (!m_frames.empty())
+ // Infinite loop where the current cursor is the same as the previous one...
+ if (prev_frame->start_pc == cursor_sp->start_pc && prev_frame->cfa == cursor_sp->cfa)
{
- // Infinite loop where the current cursor is the same as the previous one...
- if (m_frames.back()->start_pc == cursor_sp->start_pc && m_frames.back()->cfa == cursor_sp->cfa)
- {
- if (log)
- log->Printf ("th%d pc of this frame is the same as the previous frame and CFAs for both frames are identical -- stopping unwind", m_thread.GetIndexID());
- goto unwind_done;
- }
+ if (log)
+ log->Printf ("th%d pc of this frame is the same as the previous frame and CFAs for both frames are identical -- stopping unwind", m_thread.GetIndexID());
+ return nullptr;
}
cursor_sp->reg_ctx_lldb_sp = reg_ctx_sp;
- m_frames.push_back (cursor_sp);
- return true;
-
-unwind_done:
- if (log)
+ return cursor_sp;
+}
+
+bool
+UnwindLLDB::AddOneMoreFrame (ABI *abi)
+{
+ Log *log(GetLogIfAllCategoriesSet (LIBLLDB_LOG_UNWIND));
+
+ // Frame zero is a little different
+ if (m_frames.empty())
+ return false;
+
+ // If we've already gotten to the end of the stack, don't bother to try again...
+ if (m_unwind_complete)
+ return false;
+
+ CursorSP new_frame = m_candidate_frame;
+ if (new_frame == nullptr)
+ new_frame = GetOneMoreFrame(abi);
+
+ if (new_frame == nullptr)
{
- log->Printf ("th%d Unwind of this thread is complete.", m_thread.GetIndexID());
+ if (log)
+ log->Printf ("th%d Unwind of this thread is complete.", m_thread.GetIndexID());
+ m_unwind_complete = true;
+ return false;
}
- m_unwind_complete = true;
- return false;
+
+ m_frames.push_back(new_frame);
+
+ // If we can get one more frame further then accept that we get back a correct frame.
+ m_candidate_frame = GetOneMoreFrame(abi);
+ if (m_candidate_frame)
+ return true;
+
+ // We can't go further from the frame returned by GetOneMore frame. Lets try to get a
+ // different frame with using the fallback unwind plan.
+ if (!m_frames[m_frames.size() - 2]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+ {
+ // We don't have a valid fallback unwind plan. Accept the frame as it is. This is a
+ // valid situation when we are at the bottom of the stack.
+ return true;
+ }
+
+ // Remove the possibly incorrect frame from the frame list and try to add a different one with
+ // the newly selected fallback unwind plan.
+ m_frames.pop_back();
+ CursorSP new_frame_v2 = GetOneMoreFrame(abi);
+ if (new_frame_v2 == nullptr)
+ {
+ // We haven't got a new frame from the fallback unwind plan. Accept the frame from the
+ // original unwind plan. This is a valid situation when we are at the bottom of the stack.
+ m_frames.push_back(new_frame);
+ return true;
+ }
+
+ // Push the new frame to the list and try to continue from this frame. If we can get a new frame
+ // then accept it as the correct one.
+ m_frames.push_back(new_frame_v2);
+ m_candidate_frame = GetOneMoreFrame(abi);
+ if (m_candidate_frame)
+ return true;
+
+ // The new frame isn't helped in unwinding. Fall back to the original one as the default unwind
+ // plan is usually more reliable then the fallback one.
+ m_frames.pop_back();
+ m_frames.push_back(new_frame);
+ return true;
}
bool
Modified: lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.h
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.h?rev=241434&r1=241433&r2=241434&view=diff
==============================================================================
--- lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.h (original)
+++ lldb/trunk/source/Plugins/Process/Utility/UnwindLLDB.h Mon Jul 6 04:24:20 2015
@@ -65,6 +65,7 @@ protected:
DoClear()
{
m_frames.clear();
+ m_candidate_frame.reset();
m_unwind_complete = false;
}
@@ -126,14 +127,21 @@ private:
typedef std::shared_ptr<Cursor> CursorSP;
std::vector<CursorSP> m_frames;
+ CursorSP m_candidate_frame;
bool m_unwind_complete; // If this is true, we've enumerated all the frames in the stack, and m_frames.size() is the
// number of frames, etc. Otherwise we've only gone as far as directly asked, and m_frames.size()
// is how far we've currently gone.
std::vector<ConstString> m_user_supplied_trap_handler_functions;
- bool AddOneMoreFrame (ABI *abi);
- bool AddFirstFrame ();
+ CursorSP
+ GetOneMoreFrame (ABI* abi);
+
+ bool
+ AddOneMoreFrame (ABI *abi);
+
+ bool
+ AddFirstFrame ();
//------------------------------------------------------------------
// For UnwindLLDB only
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