[Lldb-commits] [lldb] [lldb] Unwind through ARM Cortex-M exceptions automatically (PR #153922)

[David Spickett via lldb-commits]

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@@ -150,3 +158,161 @@ addr_t ArchitectureArm::GetOpcodeLoadAddress(addr_t opcode_addr,
   }
   return opcode_addr & ~(1ull);
 }
+
+// The ARM M-Profile Armv7-M Architecture Reference Manual
+// "Exception return behavior" describes how the processor
+// saves registers to the stack, decrements the stack pointer,
+// puts a special value in $lr, and then calls a registered
+// exception handler routine.
+//
+// Detect that special value in $lr, and if present, add
+// unwind rules for the registers that were saved above this
+// stack frame's CFA.  Overwrite any register locations that
+// the current_unwindplan has for these registers; they are
+// not correct when we're invoked this way.
+UnwindPlanSP ArchitectureArm::GetArchitectureUnwindPlan(
+    Thread &thread, RegisterContextUnwind *regctx,
+    std::shared_ptr<const UnwindPlan> current_unwindplan) {
+
+  ProcessSP process_sp = thread.GetProcess();
+  if (!process_sp)
+    return {};
+
+  const ArchSpec arch = process_sp->GetTarget().GetArchitecture();
+  if (!arch.GetTriple().isArmMClass() || arch.GetAddressByteSize() != 4)
+    return {};
+
+  // Get the caller's LR value from regctx (the LR value
+  // at function entry to this function).
+  RegisterNumber ra_regnum(thread, eRegisterKindGeneric,
+                           LLDB_REGNUM_GENERIC_RA);
+  uint32_t ra_regnum_lldb = ra_regnum.GetAsKind(eRegisterKindLLDB);
+
+  if (ra_regnum_lldb == LLDB_INVALID_REGNUM)
+    return {};
+
+  UnwindLLDB::ConcreteRegisterLocation regloc = {};
+  bool got_concrete_location = false;
+  if (regctx->SavedLocationForRegister(ra_regnum_lldb, regloc) ==
+      UnwindLLDB::RegisterSearchResult::eRegisterFound) {
+    got_concrete_location = true;
+  } else {
+    RegisterNumber pc_regnum(thread, eRegisterKindGeneric,
+                             LLDB_REGNUM_GENERIC_PC);
+    uint32_t pc_regnum_lldb = pc_regnum.GetAsKind(eRegisterKindLLDB);
+    if (regctx->SavedLocationForRegister(pc_regnum_lldb, regloc) ==
+        UnwindLLDB::RegisterSearchResult::eRegisterFound)
+      got_concrete_location = true;
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DavidSpickett wrote:

In what circumstance do we need to lookup the PC instead of LR here?

https://github.com/llvm/llvm-project/pull/153922