[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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