[Lldb-commits] [lldb] 2d1bc9f - [lldb] Recognize MTE faults with EXC_GUARD exception type (#172579)

[via lldb-commits]

Author: Julian Lettner
Date: 2025-12-19T15:26:51-08:00
New Revision: 2d1bc9f5a212dc4c8fa14a5741af2a7a5e60ff36

URL: https://github.com/llvm/llvm-project/commit/2d1bc9f5a212dc4c8fa14a5741af2a7a5e60ff36
DIFF: https://github.com/llvm/llvm-project/commit/2d1bc9f5a212dc4c8fa14a5741af2a7a5e60ff36.diff

LOG: [lldb] Recognize MTE faults with EXC_GUARD exception type (#172579)

Recognize the new `EXC_GUARD` mach exception type
for MTE faults.  We also keep supporting the old
`EXC_BAD_ACCESS` exception type for backward
compatibility (newer LLDB on older OS).

rdar://166415268

Added: 
    

Modified: 
    lldb/source/Plugins/Process/Utility/StopInfoMachException.cpp
    lldb/source/Plugins/Process/Utility/StopInfoMachException.h

Removed: 
    


################################################################################
diff  --git a/lldb/source/Plugins/Process/Utility/StopInfoMachException.cpp b/lldb/source/Plugins/Process/Utility/StopInfoMachException.cpp
index 601cfdcb4e9f7..d374742b5722c 100644
--- a/lldb/source/Plugins/Process/Utility/StopInfoMachException.cpp
+++ b/lldb/source/Plugins/Process/Utility/StopInfoMachException.cpp
@@ -77,19 +77,28 @@ static void DescribeAddressBriefly(Stream &strm, const Address &addr,
   strm.Printf(".\n");
 }
 
+std::optional<addr_t> StopInfoMachException::GetTagFaultAddress() const {
+  const bool bad_access =
+      (m_value == 1 || m_value == 12);          // EXC_BAD_ACCESS or EXC_GUARD
+  const bool tag_fault = (m_exc_code == 0x106); // EXC_ARM_MTE_TAG_FAULT
+  // Whether the subcode (m_exc_subcode) holds the fault address.
+  const bool has_fault_addr = (m_exc_data_count >= 2);
+
+  if (bad_access && tag_fault && has_fault_addr)
+    return m_exc_subcode; // The subcode is the fault address.
+
+  return std::nullopt;
+}
+
 static constexpr uint8_t g_mte_tag_shift = 64 - 8;
 static constexpr addr_t g_mte_tag_mask = (addr_t)0x0f << g_mte_tag_shift;
 
-bool StopInfoMachException::DetermineTagMismatch(ExecutionContext &exe_ctx) {
-  const bool IsBadAccess = m_value == 1;            // EXC_BAD_ACCESS
-  const bool IsMTETagFault = (m_exc_code == 0x106); // EXC_ARM_MTE_TAG_FAULT
-  if (!IsBadAccess || !IsMTETagFault)
-    return false;
-
-  if (m_exc_data_count < 2)
+bool StopInfoMachException::DetermineTagMismatch() {
+  std::optional<addr_t> fault_address = GetTagFaultAddress();
+  if (!fault_address)
     return false;
 
-  const uint64_t bad_address = m_exc_subcode;
+  const uint64_t bad_address = *fault_address;
 
   StreamString strm;
   strm.Printf("EXC_ARM_MTE_TAG_FAULT (code=%" PRIu64 ", address=0x%" PRIx64
@@ -295,7 +304,7 @@ const char *StopInfoMachException::GetDescription() {
     case llvm::Triple::aarch64:
       if (DeterminePtrauthFailure(exe_ctx))
         return m_description.c_str();
-      if (DetermineTagMismatch(exe_ctx))
+      if (DetermineTagMismatch())
         return m_description.c_str();
       break;
 
@@ -490,6 +499,8 @@ const char *StopInfoMachException::GetDescription() {
 #endif
     break;
   case 12:
+    if (DetermineTagMismatch())
+      return m_description.c_str();
     exc_desc = "EXC_GUARD";
     break;
   }

diff  --git a/lldb/source/Plugins/Process/Utility/StopInfoMachException.h b/lldb/source/Plugins/Process/Utility/StopInfoMachException.h
index c02389e5b3642..26f93e0bb348f 100644
--- a/lldb/source/Plugins/Process/Utility/StopInfoMachException.h
+++ b/lldb/source/Plugins/Process/Utility/StopInfoMachException.h
@@ -27,7 +27,7 @@ class StopInfoMachException : public StopInfo {
   /// is auth-related failure, and returns false otherwise.
   bool DeterminePtrauthFailure(ExecutionContext &exe_ctx);
 
-  bool DetermineTagMismatch(ExecutionContext &exe_ctx);
+  bool DetermineTagMismatch();
 
 public:
   // Constructors and Destructors
@@ -48,6 +48,9 @@ class StopInfoMachException : public StopInfo {
 
   const char *GetDescription() override;
 
+  // Returns the fault address, iff this is a EXC_ARM_MTE_TAG_FAULT.
+  std::optional<lldb::addr_t> GetTagFaultAddress() const;
+
 #if defined(__APPLE__)
   struct MachException {
     static const char *Name(exception_type_t exc_type);