From 191a3c183ffdc7a48768983979a5e8509f4e8a6f Mon Sep 17 00:00:00 2001
From: yowl <scott.waye@hubse.com>
Date: Sun, 19 Apr 2020 16:28:37 -0500
Subject: [PATCH] Wasm: change NRE handling from trap to exception (#8096)

---
 .../src/CodeGen/ILToWebAssemblyImporter.cs    | 22 +++++++---
 tests/src/Simple/HelloWasm/Program.cs         | 43 +++++++++++++++++++
 2 files changed, 59 insertions(+), 6 deletions(-)

diff --git a/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs b/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs
index bcce9d469fd..1cf2787e4b6 100644
--- a/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs
+++ b/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs
@@ -4210,20 +4210,30 @@ private void ThrowIfNull(LLVMValueRef entry)
                 var resultAddress = builder.BuildIntCast(builder.BuildAlloca(LLVMTypeRef.Int32, "resultAddress"), LLVMTypeRef.CreatePointer(LLVMTypeRef.Int8, 0), "castResultAddress");
                 HandleDirectCall(helperMethod, helperMethod.Signature, arguments, null, default(LLVMValueRef), 0, NullRefFunction.GetParam(0), builder, true, resultAddress, helperMethod);
 
-                var exceptionEntry = new ExpressionEntry(GetStackValueKind(nullRefType), "RhNewObject_return", resultAddress, nullRefType);
+                var exceptionEntry = new LoadExpressionEntry(GetStackValueKind(nullRefType), "RhNewObject_return", resultAddress, nullRefType);
 
                 var ctorDef = nullRefType.GetDefaultConstructor();
 
-                var constructedExceptionObject = HandleDirectCall(ctorDef, ctorDef.Signature, new StackEntry[] { exceptionEntry }, null, default(LLVMValueRef), 0, NullRefFunction.GetParam(0), builder, false, default(LLVMValueRef), ctorDef);
+                HandleDirectCall(ctorDef, ctorDef.Signature, new StackEntry[] { exceptionEntry }, null, default(LLVMValueRef), 0, NullRefFunction.GetParam(0), builder, false, default(LLVMValueRef), ctorDef);
 
-                EmitTrapCall(builder);
+                EnsureRhpThrowEx();
+                LLVMValueRef[] args = new LLVMValueRef[] { exceptionEntry.ValueAsType(LLVMTypeRef.CreatePointer(LLVMTypeRef.Int8, 0), builder) };
+                builder.BuildCall(RhpThrowEx, args, "");
+                builder.BuildUnreachable();
                 builder.PositionAtEnd(retBlock);
                 builder.BuildRetVoid();
             }
 
-            LLVMValueRef shadowStack = _builder.BuildGEP(_currentFunclet.GetParam(0), new LLVMValueRef[] { LLVMValueRef.CreateConstInt(LLVMTypeRef.Int32, (uint)(GetTotalLocalOffset() + GetTotalParameterOffset()), false) }, String.Empty);
+            LLVMBasicBlockRef nextInstrBlock = default;
+            CallOrInvoke(false, _builder, GetCurrentTryRegion(), NullRefFunction, new List<LLVMValueRef> { GetShadowStack(), entry }, ref nextInstrBlock);
+        }
 
-            _builder.BuildCall(NullRefFunction, new LLVMValueRef[] { shadowStack, entry }, string.Empty);
+        void EnsureRhpThrowEx()
+        {
+            if (RhpThrowEx.Handle.Equals(IntPtr.Zero))
+            {
+                RhpThrowEx = Module.AddFunction("RhpThrowEx", LLVMTypeRef.CreateFunction(LLVMTypeRef.Void, new LLVMTypeRef[] { LLVMTypeRef.CreatePointer(LLVMTypeRef.Int8, 0) }, false));
+            }
         }
 
         private LLVMValueRef GetInstanceFieldAddress(StackEntry objectEntry, FieldDesc field)
@@ -4248,7 +4258,7 @@ private LLVMValueRef GetInstanceFieldAddress(StackEntry objectEntry, FieldDesc f
             {
                 untypedObjectValue = objectEntry.ValueAsType(LLVMTypeRef.CreatePointer(LLVMTypeRef.Int8, 0), _builder);
             }
-
+            ThrowIfNull(untypedObjectValue);
             if (field.Offset.AsInt == 0)
             {
                 return untypedObjectValue;
diff --git a/tests/src/Simple/HelloWasm/Program.cs b/tests/src/Simple/HelloWasm/Program.cs
index c1269e05a0a..7f53c9b7ea6 100644
--- a/tests/src/Simple/HelloWasm/Program.cs
+++ b/tests/src/Simple/HelloWasm/Program.cs
@@ -342,6 +342,8 @@ private static unsafe int Main(string[] args)
 
         TestInterlockedExchange();
 
+        TestThrowIfNull();
+
         // This test should remain last to get other results before stopping the debugger
         PrintLine("Debugger.Break() test: Ok if debugger is open and breaks.");
         System.Diagnostics.Debugger.Break();
@@ -1633,6 +1635,42 @@ static void TestInterlockedExchange()
         EndTest(exInt1 == 2 && exLong1 == 3);
     }
 
+    static void TestThrowIfNull()
+    {
+        StartTest("TestThrowIfNull");
+        ClassForNre c = null;
+        var success = true;
+        try
+        {
+            var f = c.F; //field access
+            PrintLine("NRE Field access failed");
+            success = false;
+        }
+        catch(NullReferenceException)
+        {
+        }
+        catch(Exception)
+        {
+            success = false;
+        }
+
+        try
+        {
+            var f = c.ToString(); //method access
+            PrintLine("NRE method access failed");
+            success = false;
+        }
+        catch (NullReferenceException)
+        {
+        }
+        catch (Exception)
+        {
+            success = false;
+        }
+
+        EndTest(success);
+    }
+
     static ushort ReadUInt16()
     {
         // something with MSB set
@@ -1649,6 +1687,11 @@ static ushort ReadUInt16()
     private static unsafe extern int printf(byte* str, byte* unused);
 }
 
+public class ClassForNre
+{
+    public int F;
+}
+
 public class ClassWithFloat
 {
     public static float F;