createdump: fix macOS arm64 thread IDs in LLDB

src/coreclr/debug/createdump/dumpwritermacho.cpp

@@ -16,11 +16,16 @@ DumpWriter::WriteDump()
 
     BuildThreadLoadCommands();
 
+    BuildProcessMetadataNote();
+
     uint64_t fileOffset = 0;
     if (!WriteHeader(&fileOffset)) {
         return false;
     }
 
+    m_processMetadataNote.offset = fileOffset;
+    fileOffset += m_processMetadataNote.size;
+
     TRACE("Writing %zd thread commands to core file\n", m_threadLoadCommands.size());
 
     // Write thread commands
@@ -54,6 +59,14 @@ DumpWriter::WriteDump()
         }
     }
 
+    // Write the process metadata note as the final load command
+    if (!WriteData(&m_processMetadataNote, m_processMetadataNote.cmdsize)) {
+        return false;
+    }
+    if (!WriteData(m_processMetadata.data(), m_processMetadata.size())) {
+        return false;
+    }
+
     // Write any segment alignment required to the core file
     if (alignment > 0)
     {
@@ -87,6 +100,33 @@ ConvertFlags(uint32_t flags)
     return prot;
 }
 
+void
+DumpWriter::BuildProcessMetadataNote()
+{
+    // LLDB specifies the "process metadata" LC_NOTE as compact JSON whose
+    // thread entries correspond by position to the LC_THREAD commands.
+    m_processMetadata = "{\"threads\":[";
+    bool first = true;
+    for (const ThreadInfo* thread : m_crashInfo.Threads())
+    {
+        if (!first)
+        {
+            m_processMetadata.push_back(',');
+        }
+        first = false;
+        m_processMetadata.append("{\"thread_id\":");
+        m_processMetadata.append(std::to_string(thread->Tid()));
+        m_processMetadata.push_back('}');
+    }
+    m_processMetadata.append("]}");
+
+    m_processMetadataNote.cmd = LC_NOTE;
+    m_processMetadataNote.cmdsize = sizeof(note_command);
+    static_assert(sizeof(m_processMetadataNote.data_owner) == sizeof("process metadata") - 1);
+    memcpy(m_processMetadataNote.data_owner, "process metadata", sizeof(m_processMetadataNote.data_owner));
+    m_processMetadataNote.size = m_processMetadata.size();
+}
+
 void
 DumpWriter::BuildSegmentLoadCommands()
 {
@@ -190,6 +230,9 @@ DumpWriter::WriteHeader(uint64_t* pFileOffset)
         header.sizeofcmds += segment.cmdsize;
     }
 
+    header.ncmds++;
+    header.sizeofcmds += m_processMetadataNote.cmdsize;
+
     *pFileOffset = sizeof(mach_header_64) + header.sizeofcmds;
 
     TRACE("Macho header: magic %08x cputype %08x cpusubtype %08x filetype %08x ncmds %08x sizeofcmds %08x flags %08x reserved %08x\n",

src/coreclr/debug/createdump/dumpwritermacho.h

@@ -28,6 +28,8 @@ class DumpWriter
 
     std::vector<segment_command_64> m_segmentLoadCommands;
     std::vector<ThreadCommand> m_threadLoadCommands;
+    note_command m_processMetadataNote{};
+    std::string m_processMetadata;
     BYTE m_tempBuffer[0x4000];
 
     // no public copy constructor
@@ -43,6 +45,7 @@ class DumpWriter
 
 private:
     bool WriteDiagInfo(size_t size);
+    void BuildProcessMetadataNote();
     void BuildSegmentLoadCommands();
     void BuildThreadLoadCommands();
     bool WriteHeader(uint64_t* pFileOffset);

src/coreclr/debug/createdump/specialthreadinfo.h

@@ -14,7 +14,13 @@
 
 #define SPECIAL_THREADINFO_SIGNATURE "THREADINFO"
 
+#if defined(HOST_ARM64) || defined(__arm64__) || defined(__aarch64__)
+// Apple Silicon (arm64) macOS user-space VM is 47 bits. lldb's core reader
+// rejects segments above 0x7FFF_FFFF_FFFF, so use a 47-bit-valid address.
+const uint64_t SpecialThreadInfoAddress = 0x00007ffffff00000;
+#else
 const uint64_t SpecialThreadInfoAddress = 0x7fffffff00000000;
+#endif
 
 struct SpecialThreadInfoHeader
 {