Add special diagnostic info memory region

Contains the exception record address for Native AOT crashes.

Author: Mike McLaughlin

src/coreclr/debug/createdump/crashinfo.cpp

@@ -194,6 +194,9 @@ CrashInfo::GatherCrashInfo(DumpType dumpType)
     {
         return false;
     }
+    // Add the special (fake) memory region for the special diagnostics info
+    MemoryRegion special(PF_R, SpecialDiagInfoAddress, SpecialDiagInfoAddress + PAGE_SIZE);
+    m_memoryRegions.insert(special);
 #ifdef __APPLE__
     InitializeOtherMappings();
 #endif

src/coreclr/debug/createdump/createdump.h

@@ -137,6 +137,7 @@ typedef struct
 #include "crashreportwriter.h"
 #include "dumpwriter.h"
 #include "runtimeinfo.h"
+#include "specialdiaginfo.h"
 #endif
 
 #ifndef MAX_LONGPATH

src/coreclr/debug/createdump/dumpwriter.cpp

@@ -32,6 +32,27 @@ DumpWriter::OpenDump(const char* dumpFileName)
     return true;
 }
 
+bool
+DumpWriter::WriteDiagInfo(int size)
+{
+    // Write the diagnostics info header
+    SpecialDiagInfoHeader header = {
+        {SPECIAL_DIAGINFO_SIGNATURE},
+        SPECIAL_DIAGINFO_VERSION,
+        m_crashInfo.ExceptionRecord()
+    };
+    if (!WriteData(&header, sizeof(header))) {
+        return false;
+    }
+    int alignment = size - sizeof(header);
+    assert(alignment < sizeof(m_tempBuffer));
+    memset(m_tempBuffer, 0, alignment);
+    if (!WriteData(m_tempBuffer, alignment)) {
+        return false;
+    }
+    return true;
+}
+
 // Write all of the given buffer, handling short writes and EINTR. Return true iff successful.
 bool
 DumpWriter::WriteData(int fd, const void* buffer, size_t length)

src/coreclr/debug/createdump/dumpwriterelf.cpp

@@ -176,28 +176,37 @@ DumpWriter::WriteDump()
         size_t size = memoryRegion.Size();
         total += size;
 
-        while (size > 0)
+        if (address == SpecialDiagInfoAddress)
         {
-            size_t bytesToRead = std::min(size, sizeof(m_tempBuffer));
-            size_t read = 0;
-
-            if (!m_crashInfo.ReadProcessMemory((void*)address, m_tempBuffer, bytesToRead, &read)) {
-                printf_error("Error reading memory at %" PRIA PRIx64 " size %08zx FAILED %s (%d)\n", address, bytesToRead, strerror(g_readProcessMemoryErrno), g_readProcessMemoryErrno);
+            if (!WriteDiagInfo(size)) {
                 return false;
             }
-
-            // This can happen if the target process dies before createdump is finished
-            if (read == 0) {
-                printf_error("Error reading memory at %" PRIA PRIx64 " size %08zx returned 0 bytes read: %s (%d)\n", address, bytesToRead, strerror(g_readProcessMemoryErrno), g_readProcessMemoryErrno);
-                return false;
-            }
-
-            if (!WriteData(m_tempBuffer, read)) {
-                return false;
+        }
+        else
+        {
+            while (size > 0)
+            {
+                size_t bytesToRead = std::min(size, sizeof(m_tempBuffer));
+                size_t read = 0;
+
+                if (!m_crashInfo.ReadProcessMemory((void*)address, m_tempBuffer, bytesToRead, &read)) {
+                    printf_error("Error reading memory at %" PRIA PRIx64 " size %08zx FAILED %s (%d)\n", address, bytesToRead, strerror(g_readProcessMemoryErrno), g_readProcessMemoryErrno);
+                    return false;
+                }
+
+                // This can happen if the target process dies before createdump is finished
+                if (read == 0) {
+                    printf_error("Error reading memory at %" PRIA PRIx64 " size %08zx returned 0 bytes read: %s (%d)\n", address, bytesToRead, strerror(g_readProcessMemoryErrno), g_readProcessMemoryErrno);
+                    return false;
+                }
+
+                if (!WriteData(m_tempBuffer, read)) {
+                    return false;
+                }
+
+                address += read;
+                size -= read;
             }
-
-            address += read;
-            size -= read;
         }
     }
 

src/coreclr/debug/createdump/dumpwriterelf.h

@@ -56,6 +56,7 @@ class DumpWriter
     static bool WriteData(int fd, const void* buffer, size_t length);
 
 private:
+    bool WriteDiagInfo(int size);
     bool WriteProcessInfo();
     bool WriteAuxv();
     size_t GetNTFileInfoSize(size_t* alignmentBytes = nullptr);

src/coreclr/debug/createdump/dumpwritermacho.cpp

@@ -229,7 +229,13 @@ DumpWriter::WriteSegments()
             (segment.initprot & VM_PROT_EXECUTE) ? 'x' : '-',
             segment.initprot);
 
-        if (address == SpecialThreadInfoAddress)
+        if (address == SpecialDiagInfoAddress)
+        {
+            if (!WriteDiagInfo(size)) {
+                return false;
+            }
+        }
+        else if (address == SpecialThreadInfoAddress)
         {
             // Write the header
             SpecialThreadInfoHeader header = {

src/coreclr/debug/createdump/dumpwritermacho.h

@@ -42,6 +42,7 @@ class DumpWriter
     static bool WriteData(int fd, const void* buffer, size_t length);
 
 private:
+    bool WriteDiagInfo(int size);
     void BuildSegmentLoadCommands();
     void BuildThreadLoadCommands();
     bool WriteHeader(uint64_t* pFileOffset);

src/coreclr/debug/createdump/specialdiaginfo.h

@@ -0,0 +1,32 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// ******************************************************************************
+// WARNING!!!: This code is also used by SOS in the diagnostics repo. Should be
+// updated in a backwards and forwards compatible way.
+// See: https://github.com/dotnet/diagnostics/blob/main/src/SOS/inc/specialdiaginfo.h
+// ******************************************************************************
+
+// This is a special memory region added to ELF and MachO dumps that contains extra diagnostics
+// information like the exception record for a crash for a NativeAOT app. The exception record
+// contains the pointer to the JSON formatted crash info.
+
+#define SPECIAL_DIAGINFO_SIGNATURE "DIAGINFOHEADER"
+#define SPECIAL_DIAGINFO_VERSION 1
+
+#ifdef __APPLE__
+const uint64_t SpecialDiagInfoAddress = 0x7fffffff10000000;
+#else
+#if TARGET_64BIT
+const uint64_t SpecialDiagInfoAddress = 0x00007ffffff10000;
+#else
+const uint64_t SpecialDiagInfoAddress = 0x7fff1000;
+#endif
+#endif
+
+struct SpecialDiagInfoHeader
+{
+    char Signature[16];
+    int Version;
+    uint64_t ExceptionRecordAddress;
+};