Translate code using a pointer to an assembly in Pascal - Delphi

Question

I have this code below and I want to translate it to ASM to use it in Delphi.

var
    FunctionAddressList: Array of Integer;

type TFunction = function(parameter: Integer): Integer; cdecl;

function Function(parameter: Integer): Integer;
var
    ExternFunction: TFunction;
begin
    ExternFunction := TFunction(FunctionAddressList[5]);
    Result := ExternFunction(parameter);
end;

It works fine, but when I try to execute its build version:

function Function(parameter: Integer): Integer; cdecl;
asm
  mov eax, FunctionAddressList
  jmp dword ptr [eax + 5 * 4]
end;

It should work because in C ++ it works in both directions:

void *FunctionAddressList;

_declspec(naked) int Function(int parameter)
{
    _asm mov eax, FunctionAddressList;
    _asm jmp dword ptr [eax + 5 * 4];
}

typedef int (*TFunction)(int parameter);
int Function(int parameter)
{
    TFunction ExternFunction = ((TFunction *)FunctionAddressList)[5];
    return ExternFunction(parameter);
}

But this does not work in Delphi.

In the Assembly version, it multiplies the array by 4, since this is the size of the offset between each element of the array, so both versions are equivalent.

So, I want to know why it does not work with Delphi. In Delphi, is the offset size between the Integer values ​​in the array different from C ++?

, 1, 2, 4, 6, 8 .. Array (Array of Pointer, , Integer ..), cdecl , non-asm, ASM .

.

Answer 1

:

var
  FunctionAddressList: Array of Integer;

function Bar(parameter: Integer): Integer; cdecl;
begin
  ShowMessage('Bar '+IntToStr(parameter));
end;

function Foo(parameter: Integer): Integer; cdecl;
asm
  mov eax, FunctionAddressList
  jmp dword ptr [eax + 5 * 4]
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  SetLength(FunctionAddressList, 6);
  FunctionAddressList[5]:= Integer(@Bar);
  Foo(25);
end;

Bar , , Delphi epilog Foo, Foo

0046CD30 55               push ebp
0046CD31 8BEC             mov ebp,esp
Unit1.pas.46:             mov eax, FunctionAddressList
Unit1.pas.47:             jmp dword ptr [eax + 5 * 4]
0046CD3B 5D               pop ebp
0046CD3C C3               ret

, . ,

function Foo(parameter: Integer): Integer; cdecl;
asm
  pop ebp
  mov eax, FunctionAddressList
  jmp dword ptr [eax + 5 * 4]
end;

Answer 2

Array of Integer - , . .

FunctionAddressList: ^Pointer; - , .