Eric Blake <ebl...@redhat.com> writes:
> On 05/24/2011 12:06 PM, Sam Steingold wrote:
>>> * Eric Blake <roy...@erqung.pbz> [2011-05-24 10:54:20 -0600]:
>>>
>>> Are you multi-threaded? Then you are suffering from a data race.
>>
>> I am sorry, I am afraid I am out of my depth.
>> Why is this function "suffering from a data race"?
>>
>> const char *strerror (int e) {
>> switch (e) {
>> case EINPROGRESS: return "Operation now in progress";
>> case EALREADY: return "Operation already in progress";
>> ...
>> }
> ...
> {
> static char const fmt[] = "Unknown error (%d)";
> verify (sizeof (buf) >= sizeof (fmt) + INT_STRLEN_BOUND (n));
> sprintf (buf, fmt, n);
>
>> }
>
> Try:
>
> strerror(-1) in thread 1
> strerror(-2) in thread 2
>
> POSIX explicitly allows strerror to use a static buffer, and that's
> _exactly_ what gnulib's implementation does on out-of-range input.
> Which means that "Unknown error (-1)" of thread 1 and "Unknown error
> (-2)" of thread 2 are calling sprintf on the same memory at the same
> time, and you will get indeterminate results.
Which begs the question why the error messages needs to be different for
different unknown errors? Is that required by POSIX?
/Simon
