[Python-Dev] segfaults due to hash randomization in C OrderedDict
ericsnowcurrently at gmail.com
Thu May 21 23:52:52 CEST 2015
Good catch. Unfortunately, sticking "keys = ((PyDictObject
*)od)->ma_keys;" right after "hash = ..." did not make a difference.
I still get the same segfault.
On Thu, May 21, 2015 at 11:17 AM, MRAB <python at mrabarnett.plus.com> wrote:
> On 2015-05-21 15:55, Eric Snow wrote:
>> (see http://bugs.python.org/issue16991)
>> I an working on resolving an intermittent segfault that my C
>> OrderedDict patch introduces. The failure happens in
>> test_configparser (RawConfigParser uses OrderedDict internally), but
>> only sporadically. However, Ned pointed out to me that it appears to
>> be related to hash randomization, which I have verified. I'm looking
>> into it.
>> In the meantime, here's a specific question. What would lead to the
>> pattern of failures I'm seeing? I've verified that the segfault
>> happens consistently for certain hash randomization seeds and never
>> for the rest. I don't immediately recognize the pattern but expect
>> that it would shed some light on where the problem lies. I ran the
>> following command with the OrderedDict patch applied:
>> for i in `seq 1 100`; do echo $i; PYTHONHASHSEED=$i ./python -m
>> test.regrtest -m test_basic test_configparser ; done
>> Through 100 I get segfaults with seeds of 7, 15, 35, 37, 39, 40, 42,
>> 47, 50, 66, 67, 85, 87, 88, and 92. I expect the distribution across
>> all seeds is uniform, but I haven't verified that.
> In "_odict_get_index", for example (there are others), you're caching
> PyDictKeysObject *keys = ((PyDictObject *)od)->ma_keys;
> If it resizes, you go back to the label "start", which is after that
> line, but could "ma_keys" change when it's resized?
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