On Thu, 05 Aug 2004 16:56:28 +0200, Florian Klaempfl wrote
> Ivan Stamenkovic wrote:
>
> > 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?
>
> FPC is 32 bit (flat memory modell) compiler so don't mess with
> segment registers!
>
> So:
> procedure increment(var x: dword); assembler;
> asm
> mov ebx, x
> mov eax, [ebx] { Line with the problem }
> inc eax
> mov [ebx], eax
> end;
In addition, please, note that ebx needs to be preserved in assembler
procedures in later FPC versions (although 1.0.10 is OK because of a different
default calling convention), so it would be better to either use indirect
addressing as mentioned in another message in this thread, or use a different
register (to avoid having to save ebx at the beginning and restore it at the
end) in order to ensure compatibility of your code with later FPC versions.
Tomas
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