What is the (fnptr)* type and how to create it?

Question

The following IL code creates a Type instance named (fnptr)* (token 0x2000000 - invalid, module mscorlib.dll).

ldtoken method void* ()*
call cla         


        

Answer 1

Not sure where you're seeing the FNPTR being declared.

For this code:

.assembly extern mscorlib {}

.assembly Test
{
    .ver 1:0:1:0
}
.module test.exe

.method static void main() cil managed
{
    .maxstack 1
    .entrypoint

    ldtoken method void* ()*
    call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)

    ldtoken method void* ()
    call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)

    ret
}

ILASM (4.5.22.0) outputs the following:

.method privatescope static void  main$PST06000001() cil managed
{
  .entrypoint
  // Code size       21 (0x15)
  .maxstack  1
  IL_0000:  ldtoken    method void *()*
  IL_0005:  call       class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
  IL_000a:  ldtoken    method void *()
  IL_000f:  call       class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
  IL_0014:  ret
} // end of method 'Global Functions'::main

Update #1:

Perhaps I am being dense here, but I am not seeing FNPTR being generated from this code:

typeof(StringBuilder).ToString();

The IL looks like this:

IL_0000:  nop
IL_0001:  ldtoken    [mscorlib]System.Text.StringBuilder
IL_0006:  call       class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_000b:  callvirt   instance string [mscorlib]System.Object::ToString()
IL_0010:  pop
IL_0011:  ret

The Type.ToString() call is a callvirt operation since ToString() is a virtual method.

Virtual functions are usually manifested as structs of function pointers which would, I guess, result in a FNPTR being emitted. If you omit the * in ()* resulting in (), you're now describing a function, not a function pointer.

What version of .NET are you using when you see the FNPTR? What are you using to extract the IL?