> Sanjiv Kumar Gupta wrote:
>
> > > What is stopping the value of 'foo' itself being
> > 255?
> > Programmer will get an overflow error for that
> during linking.
>
> For my curiosity, what's the background here? Do you
> really only have 256
> bytes of storage on this system?
>
That was just an example. We have an
"segment_base+offset" insn with 16-bit offset.
> If you've got eight bit registers in a larger
> address space then I'd expect
> you'd want to address data outside the first 256
> bytes, e.g. you'd actually
> want
>
> add r1, lowpart_offset(foo)
> add r2, highpart_offset(foo)
>
> in which case
>
> add r1, lowpart_offset(foo + 10)
> add r2, highpart_offset(foo + 10)
>
> would make sense.
>
> On the other hand, if you actually do only have 256
> bytes storage then you'd
> want to the link to fail anyway because the hardware
> won't cope - so the
> overflow error is as good as anything else, isn't
> it?
>
> Rup.
>
The problem at my hand is that the code like
j = 10; // global
main ()
{ int i;
i = a[j - 10];
}
doesn't work with -O2 but it works without -O2.
-O2 generates like
add1 r1, segment_base, (a - 40)
add2 r1, 40
Since 'a' is at the boundary of segment so 'a - 40'
causes relocation overflow.
But the same code works without -O2, because that
generates code like
add1 r1, segment_base, a
add2 r1, -40
add2 r1, 40
So, all I want to do is don't allow 'a - 40' in 'add1'
so that -O2 doesn't seem to be broken.
thanks
--Sanjiv
>
>
>
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