Protect against stack overflow caused by deep recursive calls

src/ARMeilleure/Instructions/InstEmitException.cs

@@ -19,7 +19,7 @@ namespace ARMeilleure.Instructions
 
             context.LoadFromContext();
 
-            context.Return(Const(op.Address));
+            InstEmitFlowHelper.EmitReturn(context, Const(op.Address));
         }
 
         public static void Svc(ArmEmitterContext context)
@@ -49,7 +49,7 @@ namespace ARMeilleure.Instructions
 
             context.LoadFromContext();
 
-            context.Return(Const(op.Address));
+            InstEmitFlowHelper.EmitReturn(context, Const(op.Address));
         }
     }
 }

src/ARMeilleure/Instructions/InstEmitException32.cs

@@ -33,7 +33,7 @@ namespace ARMeilleure.Instructions
 
             context.LoadFromContext();
 
-            context.Return(Const(context.CurrOp.Address));
+            InstEmitFlowHelper.EmitReturn(context, Const(context.CurrOp.Address));
         }
     }
 }

src/ARMeilleure/Instructions/InstEmitFlow.cs

@@ -66,7 +66,7 @@ namespace ARMeilleure.Instructions
         {
             OpCodeBReg op = (OpCodeBReg)context.CurrOp;
 
-            context.Return(GetIntOrZR(context, op.Rn));
+            EmitReturn(context, GetIntOrZR(context, op.Rn));
         }
 
         public static void Tbnz(ArmEmitterContext context) => EmitTb(context, onNotZero: true);

src/ARMeilleure/Instructions/InstEmitFlowHelper.cs

@@ -12,6 +12,10 @@ namespace ARMeilleure.Instructions
 {
     static class InstEmitFlowHelper
     {
+        // How many calls we can have in our call stack before we give up and return to the dispatcher.
+        // This prevents stack overflows caused by deep recursive calls.
+        private const int MaxCallDepth = 200;
+
         public static void EmitCondBranch(ArmEmitterContext context, Operand target, Condition cond)
         {
             if (cond != Condition.Al)
@@ -163,6 +167,19 @@ namespace ARMeilleure.Instructions
         {
             if (isReturn)
             {
+                EmitReturn(context, target);
+            }
+            else
+            {
+                EmitTableBranch(context, target, isJump: true);
+            }
+        }
+
+        public static void EmitReturn(ArmEmitterContext context, Operand target)
+        {
+            Operand nativeContext = context.LoadArgument(OperandType.I64, 0);
+            DecreaseCallDepth(context, nativeContext);
+
             if (target.Type == OperandType.I32)
             {
                 target = context.ZeroExtend32(OperandType.I64, target);
@@ -170,11 +187,6 @@ namespace ARMeilleure.Instructions
 
             context.Return(target);
         }
-            else
-            {
-                EmitTableBranch(context, target, isJump: true);
-            }
-        }
 
         private static void EmitTableBranch(ArmEmitterContext context, Operand guestAddress, bool isJump)
         {
@@ -218,6 +230,8 @@ namespace ARMeilleure.Instructions
             {
                 OpCode op = context.CurrOp;
 
+                EmitCallDepthCheckAndIncrement(context, nativeContext, guestAddress);
+
                 Operand returnAddress = context.Call(hostAddress, OperandType.I64, nativeContext);
 
                 context.LoadFromContext();
@@ -233,8 +247,41 @@ namespace ARMeilleure.Instructions
                 Operand lblContinue = context.GetLabel(nextAddr.Value);
                 context.BranchIf(lblContinue, returnAddress, nextAddr, Comparison.Equal, BasicBlockFrequency.Cold);
 
+                DecreaseCallDepth(context, nativeContext);
+
                 context.Return(returnAddress);
             }
         }
+
+        private static void EmitCallDepthCheckAndIncrement(EmitterContext context, Operand nativeContext, Operand guestAddress)
+        {
+            if (!Optimizations.EnableDeepCallRecursionProtection)
+            {
+                return;
+            }
+
+            Operand callDepthAddr = context.Add(nativeContext, Const((ulong)NativeContext.GetCallDepthOffset()));
+            Operand currentCallDepth = context.Load(OperandType.I32, callDepthAddr);
+            Operand lblDoCall = Label();
+
+            context.BranchIf(lblDoCall, currentCallDepth, Const(MaxCallDepth), Comparison.LessUI);
+            context.Store(callDepthAddr, context.Subtract(currentCallDepth, Const(1)));
+            context.Return(guestAddress);
+
+            context.MarkLabel(lblDoCall);
+            context.Store(callDepthAddr, context.Add(currentCallDepth, Const(1)));
+        }
+
+        private static void DecreaseCallDepth(EmitterContext context, Operand nativeContext)
+        {
+            if (!Optimizations.EnableDeepCallRecursionProtection)
+            {
+                return;
+            }
+
+            Operand callDepthAddr = context.Add(nativeContext, Const((ulong)NativeContext.GetCallDepthOffset()));
+            Operand currentCallDepth = context.Load(OperandType.I32, callDepthAddr);
+            context.Store(callDepthAddr, context.Subtract(currentCallDepth, Const(1)));
+        }
     }
 }

src/ARMeilleure/Optimizations.cs

@@ -9,6 +9,7 @@ namespace ARMeilleure
 
         public static bool AllowLcqInFunctionTable { get; set; } = true;
         public static bool UseUnmanagedDispatchLoop { get; set; } = true;
+        public static bool EnableDeepCallRecursionProtection { get; set; } = true;
 
         public static bool UseAdvSimdIfAvailable { get; set; } = true;
         public static bool UseArm64AesIfAvailable { get; set; } = true;

src/ARMeilleure/State/NativeContext.cs

@@ -21,6 +21,7 @@ namespace ARMeilleure.State
             public ulong ExclusiveValueLow;
             public ulong ExclusiveValueHigh;
             public int Running;
+            public int CallDepth;
         }
 
         private static NativeCtxStorage _dummyStorage = new();
@@ -257,6 +258,11 @@ namespace ARMeilleure.State
             return StorageOffset(ref _dummyStorage, ref _dummyStorage.Running);
         }
 
+        public static int GetCallDepthOffset()
+        {
+            return StorageOffset(ref _dummyStorage, ref _dummyStorage.CallDepth);
+        }
+
         private static int StorageOffset<T>(ref NativeCtxStorage storage, ref T target)
         {
             return (int)Unsafe.ByteOffset(ref Unsafe.As<NativeCtxStorage, T>(ref storage), ref target);

src/ARMeilleure/Translation/TranslatorStubs.cs

@@ -262,10 +262,18 @@ namespace ARMeilleure.Translation
 
             Operand runningAddress = context.Add(nativeContext, Const((ulong)NativeContext.GetRunningOffset()));
             Operand dispatchAddress = context.Add(nativeContext, Const((ulong)NativeContext.GetDispatchAddressOffset()));
+            Operand callDepthAddress = context.Add(nativeContext, Const((ulong)NativeContext.GetCallDepthOffset()));
 
             EmitSyncFpContext(context, nativeContext, true);
 
             context.MarkLabel(beginLbl);
+
+            if (Optimizations.EnableDeepCallRecursionProtection)
+            {
+                // Reset the call depth counter, since this is our first guest function call.
+                context.Store(callDepthAddress, Const(1));
+            }
+
             context.Store(dispatchAddress, guestAddress);
             context.Copy(guestAddress, context.Call(Const((ulong)DispatchStub), OperandType.I64, nativeContext));
             context.BranchIfFalse(endLbl, guestAddress);