Thanks for replying Jonathan > It's not supported to mix C++11 code compiled with 4.x and GCC 5+, in > any way, whether linking dynamically or statically. OK, but this is true even when the API is C? In this case no c++ structure is ever passed to mesa. If mesa was compiled with the new ABI, I should still be fine, right? > If you're only using C++98 (and of course only using the old COW > std::string in the code compiled with GCC 5+) Yeah, my gcc 5.x has _GLIBCXX_USE_CXX11_ABI=0 in the specs > This of course assumes both GCC versions are configured to be > compatible, i.e. you're not using --enable-fully-dynamic-string I'm not using many configure options, only --enable-version-specific-runtime-libs --disable-multilib So if this should work I will try to investigate it further, but I'm not sure what else I can do. gdb did not help much because if I recompile mesa without optimizations the crash does not happen. Actually disabling only inline optimization also makes the crash go away. Given that all invalid free stacks shown by valgrind contain inline functions from basic_string.h does that ring you any bells? Any other tips for debugging this?