From 8db62837e46d355bb5d0890ba09e9b2dc48a1f90 Mon Sep 17 00:00:00 2001
From: Elinor Fung <elfung@microsoft.com>
Date: Tue, 16 Apr 2024 22:08:30 -0700
Subject: [PATCH] Read contract descriptor from target

---
 src/native/managed/cdacreader/src/Target.cs | 115 ++++++++++++++++++--
 1 file changed, 104 insertions(+), 11 deletions(-)

diff --git a/src/native/managed/cdacreader/src/Target.cs b/src/native/managed/cdacreader/src/Target.cs
index 898cab774bfb5..3b4a88c8ce5ac 100644
--- a/src/native/managed/cdacreader/src/Target.cs
+++ b/src/native/managed/cdacreader/src/Target.cs
@@ -16,49 +16,142 @@ public struct TargetPointer
 
 internal sealed unsafe class Target
 {
+    private static readonly ReadOnlyMemory<byte> MagicLE = new byte[] { 0x44, 0x4e, 0x43, 0x43, 0x44, 0x41, 0x43, 0x00 }; // "DNCCDAC\0"
+    private static readonly ReadOnlyMemory<byte> MagicBE = new byte[] { 0x00, 0x43, 0x41, 0x44, 0x43, 0x43, 0x4e, 0x44 };
+
     private readonly delegate* unmanaged<ulong, byte*, uint, void*, int> _readFromTarget;
     private readonly void* _readContext;
 
     private bool _isLittleEndian;
     private int _pointerSize;
 
-    public Target(ulong _, delegate* unmanaged<ulong, byte*, uint, void*, int> readFromTarget, void* readContext)
+    private TargetPointer[] _pointerData = [];
+
+    public Target(ulong contractDescriptor, delegate* unmanaged<ulong, byte*, uint, void*, int> readFromTarget, void* readContext)
     {
         _readFromTarget = readFromTarget;
         _readContext = readContext;
 
-        // TODO: [cdac] Populate from descriptor
-        _isLittleEndian = BitConverter.IsLittleEndian;
-        _pointerSize = IntPtr.Size;
+        ReadContractDescriptor(contractDescriptor);
+    }
+
+    // See docs/design/datacontracts/contract-descriptor.md
+    private void ReadContractDescriptor(ulong address)
+    {
+        // Magic - uint64_t
+        Span<byte> buffer = stackalloc byte[sizeof(ulong)];
+        if (ReadFromTarget(address, buffer) < 0)
+            throw new InvalidOperationException("Failed to read magic.");
+
+        address += sizeof(ulong);
+        _isLittleEndian = buffer.SequenceEqual(MagicLE.Span);
+        if (!_isLittleEndian && !buffer.SequenceEqual(MagicBE.Span))
+            throw new InvalidOperationException("Invalid magic.");
+
+        // Flags - uint32_t
+        uint flags = ReadUInt32(address);
+        address += sizeof(uint);
+
+        // Bit 1 represents the pointer size. 0 = 64-bit, 1 = 32-bit.
+        _pointerSize = (int)(flags & 0x2) == 0 ? sizeof(ulong) : sizeof(uint);
+
+        // Descriptor size - uint32_t
+        uint descriptorSize = ReadUInt32(address);
+        address += sizeof(uint);
+
+        // Descriptor - char*
+        TargetPointer descriptor = ReadPointer(address);
+        address += (uint)_pointerSize;
+
+        // Pointer data count - uint32_t
+        uint pointerDataCount = ReadUInt32(address);
+        address += sizeof(uint);
+
+        // Padding
+        address += sizeof(uint);
+
+        // Pointer data - uintptr_t*
+        TargetPointer pointerData = ReadPointer(address);
+
+        // Read descriptor
+        // TODO: [cdac] Pass to JSON parser
+        Span<byte> descriptorBuffer = stackalloc byte[(int)descriptorSize];
+        if (ReadFromTarget(descriptor.Value, descriptorBuffer) < 0)
+            throw new InvalidOperationException("Failed to read descriptor.");
+
+        // Read pointer data
+        _pointerData = new TargetPointer[pointerDataCount];
+        for (int i = 0; i < pointerDataCount; i++)
+        {
+            _pointerData[i] = ReadPointer(pointerData.Value + (uint)(i * _pointerSize));
+        }
+    }
+
+    public uint ReadUInt32(ulong address)
+    {
+        if (!TryReadUInt32(address, out uint value))
+            throw new InvalidOperationException($"Failed to read uint32 at 0x{address:x8}.");
+
+        return value;
+    }
+
+    public bool TryReadUInt32(ulong address, out uint value)
+    {
+        value = 0;
+
+        Span<byte> buffer = stackalloc byte[sizeof(uint)];
+        if (ReadFromTarget(address, buffer) < 0)
+            return false;
+
+        value = _isLittleEndian
+            ? BinaryPrimitives.ReadUInt32LittleEndian(buffer)
+            : BinaryPrimitives.ReadUInt32BigEndian(buffer);
+
+        return true;
+    }
+
+    public TargetPointer ReadPointer(ulong address)
+    {
+        if (!TryReadPointer(address, out TargetPointer pointer))
+            throw new InvalidOperationException($"Failed to read pointer at 0x{address:x8}.");
+
+        return pointer;
     }
 
     public bool TryReadPointer(ulong address, out TargetPointer pointer)
     {
         pointer = TargetPointer.Null;
 
-        byte* buffer = stackalloc byte[_pointerSize];
-        ReadOnlySpan<byte> span = new ReadOnlySpan<byte>(buffer, _pointerSize);
-        if (ReadFromTarget(address, buffer, (uint)_pointerSize) < 0)
+        Span<byte> buffer = stackalloc byte[_pointerSize];
+        if (ReadFromTarget(address, buffer) < 0)
             return false;
 
         if (_pointerSize == sizeof(uint))
         {
             pointer = new TargetPointer(
                 _isLittleEndian
-                    ? BinaryPrimitives.ReadUInt32LittleEndian(span)
-                    : BinaryPrimitives.ReadUInt32BigEndian(span));
+                    ? BinaryPrimitives.ReadUInt32LittleEndian(buffer)
+                    : BinaryPrimitives.ReadUInt32BigEndian(buffer));
         }
         else if (_pointerSize == sizeof(ulong))
         {
             pointer = new TargetPointer(
                 _isLittleEndian
-                    ? BinaryPrimitives.ReadUInt64LittleEndian(span)
-                    : BinaryPrimitives.ReadUInt64BigEndian(span));
+                    ? BinaryPrimitives.ReadUInt64LittleEndian(buffer)
+                    : BinaryPrimitives.ReadUInt64BigEndian(buffer));
         }
 
         return true;
     }
 
+    private int ReadFromTarget(ulong address, Span<byte> buffer)
+    {
+        fixed (byte* bufferPtr = buffer)
+        {
+            return _readFromTarget(address, bufferPtr, (uint)buffer.Length, _readContext);
+        }
+    }
+
     private int ReadFromTarget(ulong address, byte* buffer, uint bytesToRead)
         => _readFromTarget(address, buffer, bytesToRead, _readContext);
 }