Generating IL for double arrays

Question

I’m writing some IL institutions for creating int and double arrays using System.Reflection.Emit name space.

For creating int array I’m using following code.

LocalBuilder arr = gen.DeclareLocal(typeof(int));
gen.Emit(OpCodes.Ldc_I4_1);
gen.Emit(OpCodes.Newarr, typeof(int));
gen.Emit(OpCodes.Stloc, arr);
gen.Emit(OpCodes.Ldloc, arr);
gen.Emit(OpCodes.Ldc_I4_0);
gen.Emit(OpCodes.Ldc_I4, 500);
gen.Emit(OpCodes.Stelem_I4);

gen.Emit(OpCodes.Ldloc, arr);
gen.Emit(OpCodes.Ldc_I4_0);
gen.Emit(OpCodes.Ldelem_I4);
gen.Emit(OpCodes.Call,typeof(Console).GetMethod("WriteLine",new Type[]{typeof(int)}));

It’s working as expected and prints 500 on the Console.

Same way I tried to create double array as shown below.

LocalBuilder arr = gen.DeclareLocal(typeof(double));
gen.Emit(OpCodes.Ldc_I4_1);
gen.Emit(OpCodes.Newarr, typeof(double));
gen.Emit(OpCodes.Stloc, arr);
gen.Emit(OpCodes.Ldloc, arr);
gen.Emit(OpCodes.Ldc_I4_0);
gen.Emit(OpCodes.Ldc_R8, 500D);
gen.Emit(OpCodes.Stelem_R8);

gen.Emit(OpCodes.Ldloc, arr);
gen.Emit(OpCodes.Ldc_I4_0);
gen.Emit(OpCodes.Ldelem_I8);
gen.Emit(OpCodes.Call,typeof(Console).GetMethod("WriteLine",new Type[]{typeof(double)}));

Unfortunately this doesn’t work and when I inspect generated assembly using pereview it gave me following error.

Microsoft (R) .NET Framework PE Verifier.  Version  4.0.30319.1
Copyright (c) Microsoft Corporation.  All rights reserved.

[IL]: Error: [C:\temp\Research\Research\bin\Debug\MyMod.exe : Foo::Main][offset 0x00000006][found ref array md
array 'System.Double[]'][expected Double] Unexpected type on the stack.
[IL]: Error: [C:\temp\Research\Research\bin\Debug\MyMod.exe : Foo::Main][offset 0x00000012] Expected single di
mension array.
2 Error(s) Verifying MyMod.exe

Furthermore, I inspected generated assembly using ildasm

.method privatescope static void  Main$PST06000001() cil managed
{
  .entrypoint
  // Code size       28 (0x1c)
  .maxstack  3
  .locals init (float64 V_0)
  IL_0000:  ldc.i4.1
  IL_0001:  newarr     [mscorlib]System.Double
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  ldc.i4.0
  IL_0009:  ldc.r8     500.
  IL_0012:  stelem.r8
  IL_0013:  ldloc.0
  IL_0014:  ldc.i4.0
  IL_0015:  ldelem.i8
  IL_0016:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_001b:  ret
} // end of method Foo::Main

Do you have any idea?

Answer 1

LocalBuilder arr = gen.DeclareLocal(typeof(int));
gen.Emit(OpCodes.Ldc_I4_1);
gen.Emit(OpCodes.Newarr, typeof(int));
gen.Emit(OpCodes.Stloc, arr);

Why is the arr not of type int[]?

I am certain peverify would complain for both versions.

The fact that it runs for the first version is simply 'luck'*.

* The reason is much more complex.