Why can't I use compiler intrinsics in an asm block?

Question

Is this a compiler bug?

program Project44;
{$APPTYPE CONSOLE}
uses
  System.SysUtils;

function Test: integer;
asm
  xor eax,eax
  add eax,SizeOf(NativeInt);
end;

begin
  WriteLn(Test);  //Typically outputs 31 or 49
  {$ifdef CPUX86}
  WriteLn('should be 4');
  {$else}
  {$ifdef CPUX64}
  WriteLn('should be 8');
  {$endif}{$endif}
  ReadLn
end.

This program outputs all kinds of things, except for 4/8.

Is this an bug or is it documented that I cannot use SizeOf and other compiler intrinsics in assembler?
If I would want to use SizeOf(xx) in an asm block what do I do?

Answer 1

You cannot use compiler intrinsics because they are processed by the Delphi compiler rather than the assembler. Intrinsics are resolved by the Pascal compiler processing and parsing Pascal expressions, and then emitting code. That's the job of a compiler rather than an assembler. At least, that's my mental model.

In the case of SizeOf you need to use the type assembly expression operator:

add eax, type NativeInt

Or indeed:

function Test: integer;
asm
  mov eax, type NativeInt
end;

This function performs as you expect.

Documentation here: Assembly Expressions, Expression Operators.

And yes, the fact that your code compiles should be considered a bug.