2013/11/25 Guy Harris <g...@alum.mit.edu>:
>
> On Nov 24, 2013, at 5:37 PM, Bálint Réczey <bal...@balintreczey.hu> wrote:
>
>> I tried to trigger a crash using GCC and -ftrapv without success while
>> the clang-compiled binary crashed as expected:
>
> Reproduced with clang on (x86-64) OS X.
>
> The problem is in
>
> PRIVATE int strhash(const char *x)
> {
> int h = 0;
> while( *x) h = h*13 + *(x++);
> return h;
> }
>
> In practice, the result of the hash function is taken modulo the hash table
> size, and that's always done with &, so, in practice, it's safe if it
> overflows.
>
> Perhaps it should do the calculation with unsigned integers and return an
> unsigned integer, however.
Yes, signed int overflow yields undefined behaviour, but the result of
unsigned overflow is defined thus the code above is invalid C.
At least we (you) found a real problem by temporarily enabling the
broken -ftrapv. :-)
Cheers,
Balint
___________________________________________________________________________
Sent via: Wireshark-dev mailing list <wireshark-dev@wireshark.org>
Archives: http://www.wireshark.org/lists/wireshark-dev
Unsubscribe: https://wireshark.org/mailman/options/wireshark-dev
mailto:wireshark-dev-requ...@wireshark.org?subject=unsubscribe
