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[lldb] Recognize MTE fault Mach exceptions #159117

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Merged
merged 1 commit into from
Sep 17, 2025
Merged

[lldb] Recognize MTE fault Mach exceptions #159117

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31 changes: 31 additions & 0 deletions lldb/source/Plugins/Process/Utility/StopInfoMachException.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,35 @@ static void DescribeAddressBriefly(Stream &strm, const Address &addr,
strm.Printf(".\n");
}

static constexpr uint8_t g_mte_tag_shift = 64 - 8;
static constexpr uintptr_t g_mte_tag_mask = (uintptr_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)
return false;

const uint64_t bad_address = m_exc_subcode;

StreamString strm;
strm.Printf("EXC_ARM_MTE_TAG_FAULT (code=%" PRIu64 ", address=0x%" PRIx64
")\n",
m_exc_code, bad_address);

const uint8_t tag = (bad_address & g_mte_tag_mask) >> g_mte_tag_shift;
const uint64_t canonical_addr = bad_address & ~g_mte_tag_mask;
strm.Printf(
"Note: MTE tag mismatch detected: pointer tag=%d, address=0x%" PRIx64,
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@DavidSpickett DavidSpickett Sep 16, 2025

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The Linux version will go and fetch the allocation tag, but I am not sure whether you have access to process here to do that.

tag, canonical_addr);
m_description = std::string(strm.GetString());

return true;
}

bool StopInfoMachException::DeterminePtrauthFailure(ExecutionContext &exe_ctx) {
bool IsBreakpoint = m_value == 6; // EXC_BREAKPOINT
bool IsBadAccess = m_value == 1; // EXC_BAD_ACCESS
Expand Down Expand Up @@ -266,6 +295,8 @@ const char *StopInfoMachException::GetDescription() {
case llvm::Triple::aarch64:
if (DeterminePtrauthFailure(exe_ctx))
return m_description.c_str();
if (DetermineTagMismatch(exe_ctx))
return m_description.c_str();
break;

default:
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2 changes: 2 additions & 0 deletions lldb/source/Plugins/Process/Utility/StopInfoMachException.h
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,8 @@ class StopInfoMachException : public StopInfo {
/// is auth-related failure, and returns false otherwise.
bool DeterminePtrauthFailure(ExecutionContext &exe_ctx);

bool DetermineTagMismatch(ExecutionContext &exe_ctx);

public:
// Constructors and Destructors
StopInfoMachException(Thread &thread, uint32_t exc_type,
Expand Down
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