Hi,
this is an announcement to make you aware of a GCC compiler bug that
caused us a lot of grief. This bug affects the C++11 version of the
VectorT class in OpenMesh (and hence also any Vec(2/3/4)(d/f/i)
typedef). Since OpenFlipper heavily depends on the OpenMesh vector
class, it is affected as well.
This bug only affects you, if
* you are using OpenMesh's vector class (possibly indirectly)
* and you are using GCC >= 4.9 and < 6.0
* and you are compiling with -O3 (that's default in release mode)
* and you are compiling with -std=c++11 (or c++0x or c++14).
If these four conditions are satisfied then the compiler sometimes
generates SSE instructions (which require 16 byte alignment) using
memory addresses that are not 16-byte-aligned. Since these errors lead
to segfaults, suggesting that you tried to access invalid memory
addresses, they are extremely hard to recognize and debug.
There are several workarounds:
* Use GCC <= 4.8 or use GCC >= 6.0
* or use clang
* or use -O2 (instead of -O3)
* or use -O3 -march=<architecture> for an architecture that supports
AVX. This way the compiler will generate AVX instead of SSE instructions
which do allow unaligned memory access at a small performance penalty.
This is the corresponding bug report in GCC:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66598
We are currently working on adding a unit test that exposes this bug.
Best
Hans-Christian Ebke
--
Dipl.-Inform. Hans-Christian Ebke
RWTH Aachen University
Department for Computer Graphics, Multimedia, and Computer Vision
Ahornstraße 55
52074 Aachen
Building E3, Room 114
Phone: +49 241 8021803
