https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79341
--- Comment #48 from Ulrich Weigand <uweigand at gcc dot gnu.org> --- s390(x) has -fasynchronous-unwind-tables on by default anyway, and .eh_frame based DWARF unwinding is the only way to create stack backtraces that always works. However, I understood that asan deliberately doesn't want to use DWARF unwinding for the the malloc/free case since it can be slow. That's why Marcin actually added -mbackchain to LLVM in the first place. (We've had -mbackchain in GCC forever, but it has defaulted to off for a very long time.) I don't think we should switch to *always* using backchain unwinding in asan, since system libraries on s390 will be built without backchain. However, switching -mbackchain on by default when building for asan might make sense.
