Re: [fpc-pascal]Var parameter passing to asm procedure

[Nelson M. Sicuro]

The asm block can be this way:

procedure increment(var x: dword); assembler;
asm
  inc [eax]
end;

You don't need to worry about segment registers, but don't mess with them!
I assume that the parameter x is passed on the eax register as Delphi does.
Please correct me if I'm wrong...

Hi,

I have a problem when trying to pass some variable parameters to a
procedure writen using integrated assembler. I have reduced the
problem to the following code:

program IncrementDemo;
{$R+}
{$asmmode intel}

var
   a: dword;

procedure increment(var x: dword); assembler;
   asm
      push ds { Is DS saved by default? }

      lds ebx, x
      mov eax, [ebx]     { Line with the problem }
      inc eax
      mov [ebx], eax

      pop ds
   end;

begin
   write('Enter a number: ');
   readln(a);
   increment(a);
   writeln('Result is: ', a, '.')
end.

Line with the problem is marked above. If I tried using
mov eax, [bx]
integrated environment would report that 16-bit references are not
supported. With EBX instead of BX program reports run-time error 216.

I have tried using both DOS and Win32 targets. FPC 1.0.10, Win32.

Another Q: Is it necessary to save the segment registers' contents
when entering an assembler procedure?

Thanks,
Ivan

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