Hi,
> I found strange and undocumented behaviour in kernel function INT21h/AX=6501h
> I wanted to report this as a bug but MS-DOS 7.1 has exactly the same
> behaviour.
> We have this snippet of code:
> var a:array[0..255] of byte;
> begin
> asm
> seges lea di,a
> mov bx,0ffffh
> mov dx,0ffffh
> mov cx,256
> mov ax,6501h
> int 21h
> end;
> It should return my country code and code page. But it sometimes works and
> sometimes not.
> It depends on values in A array.
> If A is zeroed (for i:=0 to 255 do a[i]:=0) it works.
> If A is assigned to constant value (for i:=0 to 255 do a[i]:=2) it works.
> But if I make: "for i:=0 to 255 do a[i]:=i" it does not work.
> This behaviour is not documented in RBIL.
> However MS-DOS 7.1 acts in same way as FreeDOS so I don't know whether is this
> bug or "feature".
it's simply a bug in your program.
ES:DI -> country information buffer (see #01750)
but your code does not load ES. so ES most likely points 'somewhere'
where you don't expect it.
push ss
pop es
should work (otherwise use a debugger)
> If A is assigned to constant value (for i:=0 to 255 do a[i]:=2) it works.
because your smart compiler turns this into something like
push ss
pop es
mov cx,256
mov al,2
rep stosb
and now es points to right segment.
Tom
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Mit freundlichen Grüßen/Kind regards
Tom Ehlert
+49-241-79886
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