1 files changed, 149 insertions, 0 deletions
diff --git a/ARMeilleure/Translation/JumpTable.cs b/ARMeilleure/Translation/JumpTable.cs
new file mode 100644
index 00000000..5cad2944
--- /dev/null
+++ b/ARMeilleure/Translation/JumpTable.cs
@@ -0,0 +1,149 @@
+using ARMeilleure.Memory;
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using System.Threading;
+
+namespace ARMeilleure.Translation
+{
+    class JumpTable
+    {
+        public static JumpTable Instance { get; }
+
+        static JumpTable()
+        {
+            Instance = new JumpTable();
+        }
+
+        // The jump table is a block of (guestAddress, hostAddress) function mappings.
+        // Each entry corresponds to one branch in a JIT compiled function. The entries are
+        // reserved specifically for each call.
+        // The _dependants dictionary can be used to update the hostAddress for any functions that change.
+
+        public const int JumpTableStride = 16; // 8 byte guest address, 8 byte host address
+
+        private const int JumpTableSize = 1048576;
+
+        private const int JumpTableByteSize = JumpTableSize * JumpTableStride;
+
+        // The dynamic table is also a block of (guestAddress, hostAddress) function mappings.
+        // The main difference is that indirect calls and jumps reserve _multiple_ entries on the table.
+        // These start out as all 0. When an indirect call is made, it tries to find the guest address on the table.
+
+        // If we get to an empty address, the guestAddress is set to the call that we want.
+
+        // If we get to a guestAddress that matches our own (or we just claimed it), the hostAddress is read.
+        // If it is non-zero, we immediately branch or call the host function.
+        // If it is 0, NativeInterface is called to find the rejited address of the call.
+        // If none is found, the hostAddress entry stays at 0. Otherwise, the new address is placed in the entry.
+
+        // If the table size is exhausted and we didn't find our desired address, we fall back to requesting 
+        // the function from the JIT.
+
+        private const int DynamicTableSize = 1048576;
+
+        public const int DynamicTableElems = 1;
+
+        public const int DynamicTableStride = DynamicTableElems * JumpTableStride;
+
+        private const int DynamicTableByteSize = DynamicTableSize * JumpTableStride * DynamicTableElems;
+
+        private int _tableEnd = 0;
+        private int _dynTableEnd = 0;
+
+        private ConcurrentDictionary<ulong, TranslatedFunction> _targets;
+        private ConcurrentDictionary<ulong, LinkedList<int>> _dependants; // TODO: Attach to TranslatedFunction or a wrapper class.
+
+        private ReservedRegion _jumpRegion;
+        private ReservedRegion _dynamicRegion;
+        public IntPtr JumpPointer => _jumpRegion.Pointer;
+        public IntPtr DynamicPointer => _dynamicRegion.Pointer;
+
+        public JumpTable()
+        {
+            _jumpRegion = new ReservedRegion(JumpTableByteSize);
+            _dynamicRegion = new ReservedRegion(DynamicTableByteSize);
+
+            _targets = new ConcurrentDictionary<ulong, TranslatedFunction>();
+            _dependants = new ConcurrentDictionary<ulong, LinkedList<int>>();
+        }
+
+        public void RegisterFunction(ulong address, TranslatedFunction func) {
+            address &= ~3UL;
+            _targets.AddOrUpdate(address, func, (key, oldFunc) => func);
+            long funcPtr = func.GetPointer().ToInt64();
+
+            // Update all jump table entries that target this address.
+            LinkedList<int> myDependants;
+            if (_dependants.TryGetValue(address, out myDependants)) 
+            {
+                lock (myDependants)
+                {
+                    foreach (var entry in myDependants)
+                    {
+                        IntPtr addr = _jumpRegion.Pointer + entry * JumpTableStride;
+                        Marshal.WriteInt64(addr, 8, funcPtr);
+                    }
+                }
+            }
+        }
+
+        public int ReserveDynamicEntry(bool isJump)
+        {
+            int entry = Interlocked.Increment(ref _dynTableEnd);
+            if (entry >= DynamicTableSize)
+            {
+                throw new OutOfMemoryException("JIT Dynamic Jump Table exhausted.");
+            }
+
+            _dynamicRegion.ExpandIfNeeded((ulong)((entry + 1) * DynamicTableStride));
+
+            // Initialize all host function pointers to the indirect call stub.
+
+            IntPtr addr = _dynamicRegion.Pointer + entry * DynamicTableStride;
+            long stubPtr = (long)DirectCallStubs.IndirectCallStub(isJump);
+
+            for (int i = 0; i < DynamicTableElems; i++)
+            {
+                Marshal.WriteInt64(addr, i * JumpTableStride + 8, stubPtr);
+            }
+
+            return entry;
+        }
+
+        public int ReserveTableEntry(long ownerAddress, long address, bool isJump)
+        {
+            int entry = Interlocked.Increment(ref _tableEnd);
+            if (entry >= JumpTableSize)
+            {
+                throw new OutOfMemoryException("JIT Direct Jump Table exhausted.");
+            }
+
+            _jumpRegion.ExpandIfNeeded((ulong)((entry + 1) * JumpTableStride));
+
+            // Is the address we have already registered? If so, put the function address in the jump table.
+            // If not, it will point to the direct call stub.
+            long value = (long)DirectCallStubs.DirectCallStub(isJump);
+            TranslatedFunction func;
+            if (_targets.TryGetValue((ulong)address, out func))
+            {
+                value = func.GetPointer().ToInt64();
+            }
+
+            // Make sure changes to the function at the target address update this jump table entry.
+            LinkedList<int> targetDependants = _dependants.GetOrAdd((ulong)address, (addr) => new LinkedList<int>());
+            lock (targetDependants)
+            {
+                targetDependants.AddLast(entry);
+            }
+
+            IntPtr addr = _jumpRegion.Pointer + entry * JumpTableStride;
+
+            Marshal.WriteInt64(addr, 0, address);
+            Marshal.WriteInt64(addr, 8, value);
+
+            return entry;
+        }
+    }
+}