[Python-Dev] segfaults due to hash randomization in C OrderedDict

Eric Snow ericsnowcurrently at gmail.com
Thu May 21 16:55:06 CEST 2015

(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.



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