#14501: Fix memory allocation problems in data_structures_pyx.pxi
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Reporter: dcoudert | Owner: joyner
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.10
Component: group theory | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: David Coudert | Merged in:
Dependencies: | Stopgaps:
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Old description:
> The following test causes a segfault on my computer (Intel(R) Xeon(R) CPU
> W3520 @ 2.67GHz / 4GB ram / linux)
> {{{
> sage: G = graphs.CompleteGraph(10)
> sage: GG = G.line_graph().line_graph().line_graph()
> sage: H = GG.relabel(inplace=False)
> sage: GG.is_isomorphic(H)
> ...
> sage: line 135: 3438 Segmentation fault (core dumped)
> "$SAGE_ROOT/spkg/bin/sage" "$@"
> }}}
> Tracking the segfault, I ended up in the {{{SC_new}}} of
> {{{sage/groups/perm_gps/partn_ref/data_structures_pyx.pxi}}}
>
> This patch fix some assignments performed before testing memory
> allocations and other similar stuff, but does not fix my problem.
New description:
The following test causes a segfault on my computer (Intel(R) Xeon(R) CPU
W3520 @ 2.67GHz / 4GB ram / linux)
{{{
sage: G = graphs.CompleteGraph(10)
sage: GG = G.line_graph().line_graph().line_graph()
sage: H = GG.relabel(inplace=False)
sage: GG.is_isomorphic(H)
...
sage: line 135: 3438 Segmentation fault (core dumped)
"$SAGE_ROOT/spkg/bin/sage" "$@"
}}}
Tracking the segfault, I ended up in the {{{SC_new}}} of
{{{sage/groups/perm_gps/partn_ref/data_structures_pyx.pxi}}}
This patch fix some assignments performed before testing memory
allocations and other similar stuff, but does not fix my problem.
Apply:
* trac_14501.2.patch
--
Comment (by dcoudert):
> Moving the two assignment can avoid a segfault alright,
Yes
> replacing a malloc by a calloc is unnecessary unless proven otherwise,
Proof: With malloc, C allocates a contiguous segment of memory. However,
this block ''is not initialized''! type "man malloc" in your terminal of
go to http://man7.org/linux/man-pages/man3/malloc.3.html.
With calloc, the memory is initialized to 0 or NULL. \qed
In any case, it is always safer to ensure that variables are initialized.
> and splitting a loop into two may also be unnecessary if the two vectors
are only allocated together (and checked at that time).
Ok.
-----
I forgot to tick "replace" while uploading update patch.
Apply: trac_14501.2.patch
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14501#comment:4>
Sage <http://www.sagemath.org>
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