Re: [Boost-bugs] [Boost C++ Libraries] #12861: Segmentation fault when creating R-tree with packing algorithm with gcc4.8.2

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #12861: Segmentation fault when creating R-tree with packing algorithm with gcc4.8.2
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-02-25 00:35:09

#12861: Segmentation fault when creating R-tree with packing algorithm with
gcc4.8.2
---------------------------------+----------------------
  Reporter:  michael.moessner@…  |      Owner:  awulkiew
      Type:  Bugs                |     Status:  new
 Milestone:  To Be Determined    |  Component:  geometry
   Version:  Boost 1.63.0        |   Severity:  Problem
Resolution:                      |   Keywords:  rtree
---------------------------------+----------------------

Comment (by awulkiew):

 I was able to reproduce it. It is a bug in libstdc++ in
 `std::nth_element()` function, see:
 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58800


 For your data `__unguarded_partition` goes out of bounds for a case
 similar to this (values below are z coordinates of centroids of some
 boxes):

 {{{
 std::vector<float> vec = {3.94167948, 2.87522459, 4.17142391, 3.00844622};
 std::nth_element(vec.begin(), vec.begin() + 2, vec.end());
 }}}

 It seems that `std::sort` doesn't have this problem so it could be called
 instead for specific version of gcc/libstdc++. So instead of a SEGFAULT
 the rtree would be slower. If I figured out how reliable is the timestamp
 defined by `__GLIBCXX__` in this case I could conditionally call
 `std::sort`. At the GCC bug page they wrote that several GCC versions were
 affected (Fixed for 4.7.4/4.8.3/4.9.0.) and the timestamp may be set to
 different value for different compilers, so IDK. At the moment I could
 enable it for this specific version I've used, `__GLIBCXX__` is
 `20131016`. Is it the same for you? Do you have any suggestions?

 As a workaround you can either update gcc/libstdc++ or alter your local
 copy of Boost by replacing `std::nth_element` calls with `std::sort`
 calls. Just use `grep` to find them in `boost/geometry`. There are some
 calls in the rstar balancing algorithm and one call in packing algorithm,
 here:
 https://github.com/boostorg/geometry/blob/develop/include/boost/geometry/index/detail/rtree/pack_create.hpp#L70

 which could be replaced with:


 {{{
 std::sort(first, last, point_entries_comparer<I>());
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12861#comment:6>
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