[fpc-devel]Re: Latest status

[Stefan Ziegenbalg]

Pierre Muller wrote:
> 
> You will get troubles anyway if address arithmetic is wrong:
> 
>   - on linux the stack is often above the 0x80000000,

Yes, it depends on the kernel (settings). (Here stack starts/ends at
$C0000000 )

>   So any error in using signed operation could
> already break small program...

What I mean with "address arithemtic" is this:

var i    : longint;
    m,l  : ^longint;
begin
...
i:=1234;
m[i]:=l[i*6+5678];
end.

It's not possible to control how "i*6+5678" is calculated. The compiler
translates this example to:

	movl	$1234,_I
	movl	_M,%eax
	movl	_I,%edx
	movl	_L,%ebx
	movl	_I,%ecx
	imull	$6,%ecx
	addl	$5678,%ecx
	movl	(%ebx,%ecx,4),%edi
	movl	%edi,(%eax,%edx,4)

That means integer multiply. But in this case signed and unsigned
multiply should be the same ("mul reg,mem" does not exist).

So in this example it should be possible to access more then 2GB. 

Best regards,
Stefan

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