Segmentation fault with g++ and optimization flags

[cphyc]

The test test_01c_zoom_grid fails with a segfault.

Configuration

• Linux (archlinux, kernel: 5.10.11-arch1-1 #1 SMP PREEMPT)
• g++ (GCC) 10.2.0
• Compilation flags: -g -O2

Note that with the same configuration and -O1 or -O0, the tests all seem to work.

Steps to reproduce

Compile the code and run the parameter file tests/test_01c_zoom_grid/paramfile.txt.

Debugging

When debugging, it seems the issue comes the variable valsForInterpolation being unallocated before being used. The variable is created here https://github.com/pynbody/genetIC/blob/6683d294dbaeeb788d5302092594cfe4bb01d242/genetIC/src/simulation/field/field.hpp#L395 The line where the segfault is reported is somewhere around here (not exact location because of the optimization flags). https://github.com/pynbody/genetIC/blob/0b75bf8cf5df71574a1939dd815dae1723900365/genetIC/src/simulation/field/field.hpp#L298-L299

[cphyc]

Further investigation:

• with g++-5 (GCC) 5.5.0 the segfault disappears
• with any version of gcc, it warns about the faulty line as follows:

  cc1plus: warning: function returns address of local variable [-Wreturn-local-addr]
  In file included from src/tools/numerics/fourier.hpp:15,
               from src/ic.hpp:15,
               from src/main.cpp:9:
  [...]/genetIC/genetIC/src/simulation/field/field.hpp:386:46: note: declared here
  386 |         return cache::cachedInterpolators.get(key).get();
    |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
  [...]/genetIC/genetIC/src/simulation/field/field.hpp:382:12: note: declared here
  382 |       auto result = cache::cachedInterpolators.get(key);
    |            ^~~~~~

[apontzen]

Ahah, that's really useful. Yes I begin to see the problem.