* Ingo Molnar <[email protected]> wrote:
> We could do something like:
>
> c = *(unsigned long *)(src+res);
> *(unsigned long *)(dest+res) = c;
>
> if (has_zero(c, &data, &constants)) {
> unsigned int zero_pos;
>
> data = prep_zero_mask(c, data, &constants);
> data = create_zero_mask(data);
>
> zero_pos = find_zero(data);
> res += zero_pos;
>
> memset(dest+res, 0, sizeof(long)-zero_pos);
>
> return res;
> }
>
> I.e. the extra memset() clears out the partial word (if any) after the NUL.
A slightly more paranoid version would be:
c = *(unsigned long *)(src+res);
if (has_zero(c, &data, &constants)) {
unsigned int zero_pos;
data = prep_zero_mask(c, data, &constants);
data = create_zero_mask(data);
zero_pos = find_zero(data);
/* Clear out undefined data within the final word after
the NUL: */
memset((void *)&c + zero_pos, 0, sizeof(long)-zero_pos);
*(unsigned long *)(dest+res) = c;
return res+zero_pos;
}
*(unsigned long *)(dest+res) = c;
This would solve any theoretical races in the _target_ buffer: if the target
buffer may be copied to user-space in a racy fashion and we don't ever want it
to
have undefined data, then this variant does the tail-zeroing of the final word
in
the temporary copy, not in the target buffer.
Still untested.
Thanks,
Ingo
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