Le 18 déc. 2013 à 00:55, Evan Huus <eapa...@gmail.com> a écrit : > On Tue, Dec 17, 2013 at 6:13 PM, Pascal Quantin > <pascal.quan...@gmail.com> wrote: >> Hi Even, >> >> in 3GPP world BCD encoding starts with the least significant nibble. That's >> why tvb_bcd_dig_to_wmwm_packet_str() behaves like this. Changing it to >> decode the most significant nibble first would break all the dissectors >> currently using this function. > > OK, just wondering. > >> The "stop condition" for the most significant nibble set to 0xf is just to >> detect the filler digit in case you have an odd number of digits. In case of >> even number, the length itself is sufficient and you do not need a filler, >> so no "stop condition" is required. > > In that case, what should the decoder do if it encounters a 0xf nibble > embedded in a value (ie due to a malformed packet instead of > indicating a stop condition)? Currently our behaviour is rather > undefined: > - if 0xf is in the high nibble, decoding stops even though the whole > length has not yet been decoded (ie if we pass a len of 12 but the > very first nibble is 0xf then we don't decode anything at all) > - if 0xf is in the low nibble, we read past the end of the digit array > (dgt_set_t) and decode it as a garbage value > > Throwing an exception seems a little extreme, but I'm not sure what else to > do.
What about adding a new entry to the dht_set_t array and display a '?' like what we do for 0xa-0xe values? > >> 2013/12/17 Evan Huus <eapa...@gmail.com> >>> >>> Alexis's ASAN build recently caught an error in >>> tvb_bcd_dig_to_wmem_packet_str in which it appears that if the least >>> significant nibble of the decoded byte is 0xf then we read one element >>> past the end of the 14-element digit array. >>> >>> If the most significant nibble is 0xf we treat that as a stop >>> condition. Is the correct approach to treat a least significant nibble >>> of 0xf as a stop condition also? >>> >>> While in the neighbourhood - shouldn't we be decoding the more >>> significant nibble first, not second? Wiki states that most BCD >>> implementations are big-endian... >>> >>> Cheers, >>> Evan >>> >>> ___________________________________________________________________________ >>> 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 >> >> >> >> ___________________________________________________________________________ >> 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 > ___________________________________________________________________________ > 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 ___________________________________________________________________________ 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
