On Mon, Oct 05 2015, Ingo Molnar <[email protected]> wrote:
> * Linus Torvalds <[email protected]> wrote:
>
>> On Thu, Sep 10, 2015 at 8:43 PM, Chris Metcalf <[email protected]> wrote:
>> >
>> > Please pull the following changes for 4.3 from:
>> >
>> > git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile.git
>> > strscpy
>>
>> So I finally pulled it. I like the patch, I like the new interface,
>> but despite that I wasn't really sure if I wanted to pull it in - thus
>> the long delay of me just seeing this in my list of pending pulls for
>> almost a month, but never really getting to the point where I decided
>> I want to commit to it.
>
> Interesting. I noticed that strscpy() says this in its comments:
>
> * In addition, the implementation is robust to the string changing out
> * from underneath it, unlike the current strlcpy() implementation.
Apologies for beating a dead horse, but:
c = *(unsigned long *)(src+res);
if (has_zero(c, &data, &constants)) {
data = prep_zero_mask(c, data, &constants);
data = create_zero_mask(data);
*(unsigned long *)(dest+res) = c & zero_bytemask(data);
return res + find_zero(data);
}
*(unsigned long *)(dest+res) = c;
I wonder whether an insane compiler might actually reload c before
storing to dest+res, so that we'd have exactly the same problem of
embedded nul characters? And similarly in the byte-by-byte case:
char c;
c = src[res];
dest[res] = c;
if (!c)
return res;
(yes, there's a store between the load and the test, and the compiler
probably can't know or prove that src and dest don't alias - but we're
storing c, so a sufficiently clever _and_ insane compiler could test
src[res]). Would READ_ONCE be justified?
Rasmus
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