Crash in _gui_support.color_ccs()

[jwilk]

When Gamera is built with GCC 9, test_rle.py crashes:

$ pytest test_rle.py
============================= test session starts ==============================
platform linux2 -- Python 2.7.16, pytest-4.6.5, py-1.8.0, pluggy-0.12.0
rootdir: /home/jwilk/gamera
collected 1 item

test_rle.py Segmentation fault

Backtrace:

#0  0x00007fb7e18aa603 in Gamera::RleDataDetail::RLEProxy<Gamera::RleDataDetail::RleVector<unsigned short> >::operator unsigned short (this=<synthetic pointer>) at include/rle_data.hpp:260
#1  Gamera::is_white<Gamera::RleDataDetail::RLEProxy<Gamera::RleDataDetail::RleVector<unsigned short> > > (value=...) at include/pixel.hpp:440
#2  Gamera::color_ccs<Gamera::ImageView<Gamera::RleImageData<unsigned short> > > (m=..., ignore_unlabeled=false) at include/plugins/gui_support.hpp:258
#3  0x00007fb7e18a0d6a in call_color_ccs (self=<optimized out>, args=<optimized out>) at /home/jwilk/gamera/gamera/plugins/_gui_support.cpp:275
#4  0x000056106008e0d9 in call_function (oparg=<optimized out>, pp_stack=0x7fff9951f7e8) at Python/ceval.c:4376
#5  PyEval_EvalFrameEx (f=f@entry=0x7fb7e0bb4050, throwflag=throwflag@entry=0) at Python/ceval.c:3013
...

Python backtrace:

File "/home/jwilk/.local/lib/python2.7/site-packages/gamera/plugins/gui_support.py", line 98, in __call__
  return _gui_support.color_ccs(image, ignore_unlabeled)
File "/home/jwilk/gamera/tests/test_rle.py", line 23, in test_rle1
  assert image1.color_ccs().to_string() == image2.color_ccs().to_string()
...

This was tested with:

• GCC 9.2.1
• Python 2.7.16 (built from source)
• Gamera from git master (c77194d)

The bug was originally reported in Debian:
https://bugs.debian.org/925689

[cdalitz]

Unfortunately, I do not have the opportunity to test this with gcc 9. It seems that the error occurs in is_white(). Could you test whether is_white() generally crashes for Onebit-Images in RLE encoding?

Note that we are currently in the process of porting Gamera to Python 3, which might fix inadvertently some bugs, but presumably will introduce other bugs.