Add a new idea of a "fallback" UnwindPlan to the RegisterContextLLDB
class. If we try to unwind a stack frame to find a caller stack
frame, and we fail to get a valid-looking frame, AND if the UnwindPlan
we used is an assembly-inspection based UnwindPlan, then we should
throw away the assembly-inspection UnwindPlan and try unwinding with
the architectural default UnwindPlan.
This code path won't be taken if eh_frame unwind instructions are available -
lldb will always prefer those once it's off the zeroth frame.
The problem I'm trying to fix here is the class of unwind failures that
happen when we have hand-written assembly on the stack, with no eh_frame,
and lldb's assembly parser fails to understand the assembly. People usually
write their hand-written assembly to follow the frame-pointer-preserving
conventions of the platform so the architectural default UnwindPlan will
often work. We won't have the spill location for most of the non-volatile
registers if we fall back to this, but it's better than stopping the unwind
prematurely.
This is a bit of a tricky change that I believe is correct, but if we get
unwinds that go of into the weeds / unwind bogus frames at the end of the
stack, I'll need to revisit it.
<rdar://problem/16099440>
llvm-svn: 201839
diff --git a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
index a3a7002..5db08e5 100644
--- a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
+++ b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
@@ -158,6 +158,12 @@
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 (log)
log->Printf ("%*sFrame %d did not get a RegisterContext, stopping.",
cur_idx < 100 ? cur_idx : 100, "", cur_idx);
@@ -166,6 +172,12 @@
if (!reg_ctx_sp->IsValid())
{
+ // 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 (log)
{
log->Printf("%*sFrame %d invalid RegisterContext for this frame, stopping stack walk",
@@ -175,6 +187,12 @@
}
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 (log)
{
log->Printf("%*sFrame %d did not get CFA for this frame, stopping stack walk",
@@ -189,6 +207,12 @@
// these.
if (reg_ctx_sp->IsTrapHandlerFrame() == false)
{
+ // 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 (log)
{
log->Printf("%*sFrame %d did not get a valid CFA for this frame, stopping stack walk",
@@ -199,6 +223,12 @@
}
if (!reg_ctx_sp->ReadPC (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 (log)
{
log->Printf("%*sFrame %d did not get PC for this frame, stopping stack walk",
@@ -208,6 +238,12 @@
}
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 (log)
{
log->Printf("%*sFrame %d did not get a valid PC, stopping stack walk",