[lldb][debugserver][MacOSX] Work around sanitizer misaligned address errors when reading exception data (#132193)

We've been dealing with UBSAN issues around this code for some time now
(see `9c36859b33b386fbfa9599646de1e2ae01158180` and
`1a2122e9e9d1d495fdf337a4a9445b61ca56df6f`). On recent macOS versions, a
UBSAN-enabled debugserver will crash when performing a `memcpy` of the
input `mach_exception_data_t`. The pointer to the beginning of the
exception data may not be aligned on a doubleword boundary, leading to
UBSAN failures such as:
```
$ ./bin/debugserver 0.0.0.0:5555 /Volumes/SSD/llvm-builds/llvm-worktrees/clang-work/build-sanitized-release/tools/lldb/test/Shell/Recognizer/Output/verbose_trap.test.tmp.out
/Volumes/SSD/llvm-builds/llvm-worktrees/clang-work/lldb/tools/debugserver/source/MacOSX/MachException.cpp:35:12: runtime error: store to misaligned address 0x00016ddfa634 for type 'mach_exception_data_type_t *' (aka 'long long *'), which requires 8 byte alignment
0x00016ddfa634: note: pointer points here
  02 00 00 00 03 00 01 00  00 00 00 00 11 00 00 00  00 00 00 00 00 00 00 00  08 00 00 00 00 00 00 00
              ^
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /Volumes/SSD/llvm-builds/llvm-worktrees/clang-work/lldb/tools/debugserver/source/MacOSX/MachException.cpp:35:12
```

Work around these failures by pretending the input data is a `char*`
buffer.

Drive-by changes:
* I factored out some duplicated code into a static
`AppendExceptionData` and made the types consistent

---------

Co-authored-by: Jonas Devlieghere <[email protected]>

Author: Michael137

lldb/tools/debugserver/source/MacOSX/MachException.cpp

@@ -18,9 +18,25 @@
 #include "PThreadMutex.h"
 #include "SysSignal.h"
 #include <cerrno>
+#include <inttypes.h>
 #include <sys/ptrace.h>
 #include <sys/types.h>
 
+static void AppendExceptionData(std::vector<mach_exception_data_type_t> &out,
+                                mach_exception_data_t data,
+                                mach_msg_type_number_t count) {
+  mach_exception_data_type_t buf;
+  for (mach_msg_type_number_t i = 0; i < count; ++i) {
+    // The input Data we receive need not be aligned correctly.
+    // Perform an unaligned copy by pretending we're dealing with
+    // a char* buffer. This is required to work around UBSAN/ASAN
+    // "misaligned address" errors.
+    auto *src = reinterpret_cast<char *>(data + i);
+    memcpy(&buf, src, sizeof(mach_exception_data_type_t));
+    out.push_back(buf);
+  }
+}
+
 // Routine mach_exception_raise
 extern "C" kern_return_t
 catch_mach_exception_raise(mach_port_t exception_port, mach_port_t thread,
@@ -95,20 +111,16 @@ catch_mach_exception_raise(mach_port_t exc_port, mach_port_t thread_port,
                            mach_exception_data_t exc_data,
                            mach_msg_type_number_t exc_data_count) {
   if (DNBLogCheckLogBit(LOG_EXCEPTIONS)) {
-    std::vector<uint64_t> exc_datas;
-    uint64_t tmp;
-    for (unsigned i = 0; i < exc_data_count; ++i) {
-      // Perform an unaligned copy.
-      memcpy(&tmp, &exc_data[i], sizeof(uint64_t));
-      exc_datas.push_back(tmp);
-    }
+    std::vector<mach_exception_data_type_t> exc_datas;
+    AppendExceptionData(exc_datas, exc_data, exc_data_count);
     DNBLogThreaded("::%s ( exc_port = 0x%4.4x, thd_port = 0x%4.4x, tsk_port = "
-                   "0x%4.4x, exc_type = %d ( %s ), exc_data[%d] = { 0x%llx, "
-                   "0x%llx })",
+                   "0x%4.4x, exc_type = %d ( %s ), exc_data[%d] = { 0x%" PRIx64
+                   ", "
+                   "0x%" PRIx64 " })",
                    __FUNCTION__, exc_port, thread_port, task_port, exc_type,
                    MachException::Name(exc_type), exc_data_count,
-                   (uint64_t)(exc_data_count > 0 ? exc_datas[0] : 0xBADDBADD),
-                   (uint64_t)(exc_data_count > 1 ? exc_datas[1] : 0xBADDBADD));
+                   (exc_data_count > 0 ? exc_datas[0] : 0xBADDBADD),
+                   (exc_data_count > 1 ? exc_datas[1] : 0xBADDBADD));
   }
   g_message->exc_type = 0;
   g_message->exc_data.clear();
@@ -117,7 +129,7 @@ catch_mach_exception_raise(mach_port_t exc_port, mach_port_t thread_port,
     g_message->task_port = task_port;
     g_message->thread_port = thread_port;
     g_message->exc_type = exc_type;
-    g_message->AppendExceptionData(exc_data, exc_data_count);
+    AppendExceptionData(g_message->exc_data, exc_data, exc_data_count);
     return KERN_SUCCESS;
   } else if (!MachTask::IsValid(g_message->task_port)) {
     // Our original exception port isn't valid anymore check for a SIGTRAP
@@ -129,7 +141,7 @@ catch_mach_exception_raise(mach_port_t exc_port, mach_port_t thread_port,
       g_message->task_port = task_port;
       g_message->thread_port = thread_port;
       g_message->exc_type = exc_type;
-      g_message->AppendExceptionData(exc_data, exc_data_count);
+      AppendExceptionData(g_message->exc_data, exc_data, exc_data_count);
       return KERN_SUCCESS;
     }
   }

lldb/tools/debugserver/source/MacOSX/MachException.h

@@ -70,15 +70,6 @@ class MachException {
       return (exc_type == EXC_BREAKPOINT ||
               ((exc_type == EXC_SOFTWARE) && exc_data[0] == 1));
     }
-    void AppendExceptionData(mach_exception_data_t Data,
-                             mach_msg_type_number_t Count) {
-      mach_exception_data_type_t Buf;
-      for (mach_msg_type_number_t i = 0; i < Count; ++i) {
-        // Perform an unaligned copy.
-        memcpy(&Buf, Data + i, sizeof(mach_exception_data_type_t));
-        exc_data.push_back(Buf);
-      }
-    }
     void Dump() const;
     void DumpStopReason() const;
     bool GetStopInfo(struct DNBThreadStopInfo *stop_info) const;