From 94d2ce0fcfc853a80aa918685324344f7bead8e4 Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Thu, 1 Jun 2023 14:34:05 +0200
Subject: [PATCH] Fix crash when control flow reaches end of method.

---
 .../ILPrettyTestRunner.cs                     |  6 +++
 .../TestCases/ILPretty/EmptyBodies.cs         | 14 ++++++
 .../TestCases/ILPretty/EmptyBodies.il         | 45 +++++++++++++++++++
 ICSharpCode.Decompiler/IL/ILReader.cs         | 15 +++++--
 4 files changed, 77 insertions(+), 3 deletions(-)
 create mode 100644 ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs
 create mode 100644 ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.il

diff --git a/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs b/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs
index 237bdd402..5338bb7c9 100644
--- a/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs
+++ b/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs
@@ -263,6 +263,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await Run();
 		}
 
+		[Test]
+		public async Task EmptyBodies()
+		{
+			await Run();
+		}
+
 		async Task Run([CallerMemberName] string testName = null, DecompilerSettings settings = null,
 			AssemblerOptions assemblerOptions = AssemblerOptions.Library)
 		{
diff --git a/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs
new file mode 100644
index 000000000..6945a1db1
--- /dev/null
+++ b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs
@@ -0,0 +1,14 @@
+internal class EmptyBodies
+{
+	public static void RetVoid()
+	{
+	}
+	public static int RetInt()
+	{
+		return (int)/*Error near IL_0001: Stack underflow*/;
+	}
+	public static void Nop()
+	{
+		/*Error: End of method reached without returning.*/;
+	}
+}
\ No newline at end of file
diff --git a/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.il b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.il
new file mode 100644
index 000000000..bd14a188c
--- /dev/null
+++ b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.il
@@ -0,0 +1,45 @@
+#define CORE_ASSEMBLY "System.Runtime"
+
+.assembly extern CORE_ASSEMBLY
+{
+  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
+  .ver 4:0:0:0
+}
+
+.class private auto ansi beforefieldinit EmptyBodies
+    extends [CORE_ASSEMBLY]System.Object
+{
+    // I cannot test a truly empty body because the assembler will automatically add a ret instruction.
+
+    .method public hidebysig static void RetVoid () cil managed 
+    {
+	    .maxstack 8
+		ret
+    }
+
+	.method public hidebysig static int32 RetInt () cil managed 
+    {
+	    .maxstack 8
+		ret
+    }
+
+	.method public hidebysig static void Nop () cil managed 
+    {
+	    .maxstack 8
+		nop
+    }
+
+    .method public hidebysig specialname rtspecialname 
+        instance void .ctor () cil managed 
+    {
+        // Method begins at RVA 0x206e
+        // Code size 8 (0x8)
+        .maxstack 8
+
+        IL_0000: ldarg.0
+        IL_0001: call instance void [System.Private.CoreLib]System.Object::.ctor()
+        IL_0006: nop
+        IL_0007: ret
+    } // end of method Example::.ctor
+
+} // end of class EmptyBodies
diff --git a/ICSharpCode.Decompiler/IL/ILReader.cs b/ICSharpCode.Decompiler/IL/ILReader.cs
index 89d0739ae..8b1072967 100644
--- a/ICSharpCode.Decompiler/IL/ILReader.cs
+++ b/ICSharpCode.Decompiler/IL/ILReader.cs
@@ -535,16 +535,25 @@ namespace ICSharpCode.Decompiler.IL
 			if (!block.Block.HasFlag(InstructionFlags.EndPointUnreachable))
 			{
 				// create fall through branch
-				MarkBranchTarget(reader.Offset, isFallThrough: true);
+				ILInstruction branch;
+				if (reader.RemainingBytes > 0)
+				{
+					MarkBranchTarget(reader.Offset, isFallThrough: true);
+					branch = new Branch(reader.Offset);
+				}
+				else
+				{
+					branch = new InvalidBranch("End of method reached without returning.");
+				}
 				if (block.Block.Instructions.LastOrDefault() is SwitchInstruction switchInst && switchInst.Sections.Last().Body.MatchNop())
 				{
 					// Instead of putting the default branch after the switch instruction
-					switchInst.Sections.Last().Body = new Branch(reader.Offset);
+					switchInst.Sections.Last().Body = branch;
 					Debug.Assert(switchInst.HasFlag(InstructionFlags.EndPointUnreachable));
 				}
 				else
 				{
-					block.Block.Instructions.Add(new Branch(reader.Offset));
+					block.Block.Instructions.Add(branch);
 				}
 			}
 		}