jasonmolenda created this revision.
jasonmolenda added a project: LLDB.
Herald added a subscriber: kristof.beyls.
On targets with a return address register (e.g. $lr on arm), when the unwinder
is asked to fetch the caller's pc, we rewrite that to fetch the return address
value.
However, when we're in a trap handler -- either from an interrupt or an async
signal -- we will have a full register context for the frame that was
interrupted/trapped. The unwinder correctly allows you to fetch volatile
registers when you're above a trap handler. But we are still rewriting the
"fetch the pc" request when the trap handler is asked to find the caller's
saved pc. This is incorrect, and results in lldb showing the wrong function
that was interrupted/faulted.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D75007
Files:
lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
Index: lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
===================================================================
--- lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
+++ lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
@@ -1203,9 +1203,13 @@
// If we're fetching the saved pc and this UnwindPlan defines a
// ReturnAddress register (e.g. lr on arm), look for the return address
// register number in the UnwindPlan's row.
+ // If this is a trap handler frame, we have access to the complete
+ // register context when the interrupt/async signal was received, so
+ // we need to fetch the actual saved $pc value.
if (pc_regnum.IsValid() && pc_regnum == regnum &&
m_full_unwind_plan_sp->GetReturnAddressRegister() !=
- LLDB_INVALID_REGNUM) {
+ LLDB_INVALID_REGNUM &&
+ m_frame_type != eTrapHandlerFrame) {
return_address_reg.init(
m_thread, m_full_unwind_plan_sp->GetRegisterKind(),
Index: lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
===================================================================
--- lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
+++ lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
@@ -1203,9 +1203,13 @@
// If we're fetching the saved pc and this UnwindPlan defines a
// ReturnAddress register (e.g. lr on arm), look for the return address
// register number in the UnwindPlan's row.
+ // If this is a trap handler frame, we have access to the complete
+ // register context when the interrupt/async signal was received, so
+ // we need to fetch the actual saved $pc value.
if (pc_regnum.IsValid() && pc_regnum == regnum &&
m_full_unwind_plan_sp->GetReturnAddressRegister() !=
- LLDB_INVALID_REGNUM) {
+ LLDB_INVALID_REGNUM &&
+ m_frame_type != eTrapHandlerFrame) {
return_address_reg.init(
m_thread, m_full_unwind_plan_sp->GetRegisterKind(),
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