[cdac] Read contract descriptor from target (#101208)

- Get `DotNetRuntimeContractDescriptor` address from the target
- Read contract descriptor to determine endianness and pointer size
- Parse JSON descriptor and store contracts

Author: elinor-fung

src/coreclr/debug/daccess/cdac.cpp

@@ -28,8 +28,12 @@ namespace
 
     int ReadFromTargetCallback(uint64_t addr, uint8_t* dest, uint32_t count, void* context)
     {
-        CDAC* cdac = reinterpret_cast<CDAC*>(context);
-        return cdac->ReadFromTarget(addr, dest, count);
+        ICorDebugDataTarget* target = reinterpret_cast<ICorDebugDataTarget*>(context);
+        HRESULT hr = ReadFromDataTarget(target, addr, dest, count);
+        if (FAILED(hr))
+            return hr;
+
+        return S_OK;
     }
 }
 
@@ -52,11 +56,12 @@ CDAC::CDAC(HMODULE module, uint64_t descriptorAddr, ICorDebugDataTarget* target)
         return;
     }
 
+    m_target->AddRef();
     decltype(&cdac_reader_init) init = reinterpret_cast<decltype(&cdac_reader_init)>(::GetProcAddress(m_module, "cdac_reader_init"));
     decltype(&cdac_reader_get_sos_interface) getSosInterface = reinterpret_cast<decltype(&cdac_reader_get_sos_interface)>(::GetProcAddress(m_module, "cdac_reader_get_sos_interface"));
     _ASSERTE(init != nullptr && getSosInterface != nullptr);
 
-    init(descriptorAddr, &ReadFromTargetCallback, this, &m_cdac_handle);
+    init(descriptorAddr, &ReadFromTargetCallback, m_target, &m_cdac_handle);
     getSosInterface(m_cdac_handle, &m_sos);
 }
 
@@ -77,12 +82,3 @@ IUnknown* CDAC::SosInterface()
 {
     return m_sos;
 }
-
-int CDAC::ReadFromTarget(uint64_t addr, uint8_t* dest, uint32_t count)
-{
-    HRESULT hr = ReadFromDataTarget(m_target, addr, dest, count);
-    if (FAILED(hr))
-        return hr;
-
-    return S_OK;
-}

src/coreclr/debug/daccess/cdac.h

@@ -21,7 +21,7 @@ class CDAC final
     CDAC(CDAC&& other)
         : m_module{ other.m_module }
         , m_cdac_handle{ other.m_cdac_handle }
-        , m_target{ other.m_target }
+        , m_target{ other.m_target.Extract() }
         , m_sos{ other.m_sos.Extract() }
     {
         other.m_module = NULL;
@@ -34,7 +34,7 @@ class CDAC final
     {
         m_module = other.m_module;
         m_cdac_handle = other.m_cdac_handle;
-        m_target = other.m_target;
+        m_target = other.m_target.Extract();
         m_sos = other.m_sos.Extract();
 
         other.m_module = NULL;
@@ -54,15 +54,14 @@ class CDAC final
 
     // This does not AddRef the returned interface
     IUnknown* SosInterface();
-    int ReadFromTarget(uint64_t addr, uint8_t* dest, uint32_t count);
 
 private:
     CDAC(HMODULE module, uint64_t descriptorAddr, ICorDebugDataTarget* target);
 
 private:
     HMODULE m_module;
     intptr_t m_cdac_handle;
-    ICorDebugDataTarget* m_target;
+    NonVMComHolder<ICorDebugDataTarget> m_target;
     NonVMComHolder<IUnknown> m_sos;
 };
 

src/coreclr/debug/daccess/daccess.cpp

@@ -30,6 +30,8 @@
 #include <dactablerva.h>
 #else
 extern "C" bool TryGetSymbol(ICorDebugDataTarget* dataTarget, uint64_t baseAddress, const char* symbolName, uint64_t* symbolAddress);
+// cDAC depends on symbol lookup to find the contract descriptor
+#define CAN_USE_CDAC
 #endif
 
 #include "dwbucketmanager.hpp"
@@ -5493,15 +5495,16 @@ ClrDataAccess::Initialize(void)
     IfFailRet(GetDacGlobalValues());
     IfFailRet(DacGetHostVtPtrs());
 
+// TODO: [cdac] TryGetSymbol is only implemented for Linux, OSX, and Windows.
+#ifdef CAN_USE_CDAC
     CLRConfigNoCache enable = CLRConfigNoCache::Get("ENABLE_CDAC");
     if (enable.IsSet())
     {
         DWORD val;
         if (enable.TryAsInteger(10, val) && val == 1)
         {
-            // TODO: [cdac] Get contract descriptor from exported symbol
             uint64_t contractDescriptorAddr = 0;
-            //if (TryGetSymbol(m_pTarget, m_globalBase, "DotNetRuntimeContractDescriptor", &contractDescriptorAddr))
+            if (TryGetSymbol(m_pTarget, m_globalBase, "DotNetRuntimeContractDescriptor", &contractDescriptorAddr))
             {
                 m_cdac = CDAC::Create(contractDescriptorAddr, m_pTarget);
                 if (m_cdac.IsValid())
@@ -5514,6 +5517,7 @@ ClrDataAccess::Initialize(void)
             }
         }
     }
+#endif
 
     //
     // DAC is now setup and ready to use
@@ -6946,7 +6950,7 @@ GetDacTableAddress(ICorDebugDataTarget* dataTarget, ULONG64 baseAddress, PULONG6
         return E_INVALIDARG;
     }
 #endif
-    // On MacOS, FreeBSD or NetBSD use the RVA include file
+    // On FreeBSD, NetBSD, or SunOS use the RVA include file
     *dacTableAddress = baseAddress + DAC_TABLE_RVA;
 #else
     // Otherwise, try to get the dac table address via the export symbol

src/native/managed/cdacreader/src/ContractDescriptorParser.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Contracts;
 using System.Text.Json;
 using System.Text.Json.Serialization;
@@ -23,13 +24,15 @@ public partial class ContractDescriptorParser
     /// <summary>
     ///  Parses the "compact" representation of a contract descriptor.
     /// </summary>
+    // Workaround for https://github.com/dotnet/runtime/issues/101205
+    [DynamicDependency(DynamicallyAccessedMemberTypes.All, typeof(Root))]
     public static ContractDescriptor? ParseCompact(ReadOnlySpan<byte> json)
     {
         return JsonSerializer.Deserialize(json, ContractDescriptorContext.Default.ContractDescriptor);
     }
 
     [JsonSerializable(typeof(ContractDescriptor))]
-    [JsonSerializable(typeof(int))]
+    [JsonSerializable(typeof(int?))]
     [JsonSerializable(typeof(string))]
     [JsonSerializable(typeof(Dictionary<string, int>))]
     [JsonSerializable(typeof(Dictionary<string, TypeDescriptor>))]
@@ -38,11 +41,17 @@ public partial class ContractDescriptorParser
     [JsonSerializable(typeof(TypeDescriptor))]
     [JsonSerializable(typeof(FieldDescriptor))]
     [JsonSerializable(typeof(GlobalDescriptor))]
+    [JsonSerializable(typeof(Dictionary<string, JsonElement>))]
     [JsonSourceGenerationOptions(AllowTrailingCommas = true,
                                 DictionaryKeyPolicy = JsonKnownNamingPolicy.Unspecified, // contracts, types and globals are case sensitive
                                 PropertyNamingPolicy = JsonKnownNamingPolicy.CamelCase,
                                 NumberHandling = JsonNumberHandling.AllowReadingFromString,
-                                ReadCommentHandling = JsonCommentHandling.Skip)]
+                                ReadCommentHandling = JsonCommentHandling.Skip,
+                                UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
+                                UnknownTypeHandling = JsonUnknownTypeHandling.JsonElement,
+                                Converters = [typeof(TypeDescriptorConverter),
+                                            typeof(FieldDescriptorConverter),
+                                            typeof(GlobalDescriptorConverter)])]
     internal sealed partial class ContractDescriptorContext : JsonSerializerContext
     {
     }
@@ -58,7 +67,13 @@ public class ContractDescriptor
         public Dictionary<string, GlobalDescriptor>? Globals { get; set; }
 
         [JsonExtensionData]
-        public Dictionary<string, object?>? Extras { get; set; }
+        public Dictionary<string, JsonElement>? Extras { get; set; }
+
+        public override string ToString()
+        {
+            return $"Version: {Version}, Baseline: {Baseline}, Contracts: {Contracts?.Count}, Types: {Types?.Count}, Globals: {Globals?.Count}";
+        }
+
     }
 
     [JsonConverter(typeof(TypeDescriptorConverter))]

src/native/managed/cdacreader/src/Entrypoints.cs

@@ -14,7 +14,10 @@ internal static class Entrypoints
     [UnmanagedCallersOnly(EntryPoint = $"{CDAC}init")]
     private static unsafe int Init(ulong descriptor, delegate* unmanaged<ulong, byte*, uint, void*, int> readFromTarget, void* readContext, IntPtr* handle)
     {
-        Target target = new(descriptor, readFromTarget, readContext);
+        // TODO: [cdac] Better error code/details
+        if (!Target.TryCreate(descriptor, readFromTarget, readContext, out Target? target))
+            return -1;
+
         GCHandle gcHandle = GCHandle.Alloc(target);
         *handle = GCHandle.ToIntPtr(gcHandle);
         return 0;

src/native/managed/cdacreader/src/Root.cs

@@ -0,0 +1,12 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Text.Json.Serialization;
+
+namespace Microsoft.Diagnostics.DataContractReader;
+
+internal static class Root
+{
+    // https://github.com/dotnet/runtime/issues/101205
+    public static JsonDerivedTypeAttribute[] R1 = new JsonDerivedTypeAttribute[] { null! };
+}