将在 windows 上运行的 Delphi 中的汇编程序 function 转换为 delphi/c++ 以在 ZEDC8310A5A3D57473E 上执行

Question

I have this assembler function in my application wriiten in delphi and this executes well on windows.But my requirement is to execute it on Linux as i am migrating my application on Linux. And while compiling this function in Linux i got error: "Unsupported language feature: 'ASM'".

Anybody can help or suggest how to implement it either in c++ or in delphi so that it works for Linux. sharing my code:

type 
  PVersionizedPointer = ^TVersionizedPointer; 
  TVersionizedPointer = packed record 
    Ver : NativeInt; 
    Ptr : Pointer; 
  end; 
  TVersionizedPointerStorage = array[0 .. 2 * sizeof(TVersionizedPointer) - 1] of byte; 

function GetVersionizedPointer(var PointerStorage : TVersionizedPointerStorage) : 
    PVersionizedPointer; assembler;
const
  vp_size = sizeof(TVersionizedPointer);  
      // Note: sizeof(any) inside asm is always $31
  asm
    {$ifdef CPUX86}
      add EAX, vp_size - 1
      and EAX, not(vp_size - 1)
    {$endif}
    {$ifdef CPUX64}
      mov RAX, RCX
      add RAX, vp_size - 1
      and RAX, not(vp_size - 1)
    {$endif}
  end;
end;

Answer 1

It's probably easiest just to concentrate on what the x86 version does:

function GetVersionizedPointer(var PointerStorage: TVersionizedPointerStorage): PVersionizedPointer;
const
  vp_size = sizeof(TVersionizedPointer);
asm
  add EAX, vp_size - 1
  and EAX, not(vp_size - 1)
end;

The x86 ABI means that the address of PointerStorage is passed into the function in EAX . The return value, another address, is also retuned in EAX . That knowledge lets us understand what the function does, and allows us to write it like this in Pascal:

function GetVersionizedPointer(var PointerStorage: TVersionizedPointerStorage): PVersionizedPointer;
var
  Address: NativeUInt;
begin
  Address := NativeUInt(@PointerStorage);
  Address := Address + (SizeOf(TVersionizedPointer) - 1);
  Address := Address and not (SizeOf(TVersionizedPointer) - 1);
  Result := PVersionizedPointer(Address);
end;

I've written it out rather verbosely to make it clear what each step is doing. The address variable is assigned the address of PointerStorage , and so serves the same role as EAX in the original version.

Make your life easier in the future by using this pure Pascal version, and losing the assembler code.

Answer 2

This function aim is to align the storage in memory. It is perfectly pointless in modern Intel/AMD CPUs . It may have had a benefit on a 8086 CPU, but not any more. Sounds definitively like wrong/premature optimization.

This whole alignment subroutine may just be avoided: it would make code cleaner and also faster. Just get rid of TVersionizedPointerStorage and only use TVersionizedPointer .

Not aligning the data will be faster, since you won't need to compute any alignment any more, and you would just use the needed memory, whereas TVersionizedPointerStorage is always using twice the size, so it pollutes the CPU L1 cache for no benefit, and add unneeded memory allocation.