On 7 March 2015 at 23:16, Michael Cronenworth wrote: > Hello, > > I am attempting to debug why WINE[1], when compiled with GCC 5[2] on Fedora > Rawhide, cannot run when an optimization level is specified. > > -O0 : works > -O1 : segfault > -O2 : segfault Do you have any more details available somewhere I can see them? Maybe in Fedora's bugzilla or on the devel@ list? > I have enabled -O1 flags manually and WINE works. What other settings is GCC > 5 enabling between optimization levels? I have run -Q --help=optimizers and > that's what I based my flag settings on, but there is something obviously > missing that -O1 enables. As already pointed out, turning on individual optimizations without -O has no effect. https://gcc.gnu.org/bugs/ advises "Before reporting that GCC compiles your code incorrectly, compile it with gcc -Wall -Wextra and see whether this shows anything wrong with your code. Similarly, if compiling with -fno-strict-aliasing -fwrapv -fno-aggressive-loop-optimizations makes a difference, your code probably is not correct." Although -fno-strict-aliasing is unlikely to make any difference because strict aliasing is only enabled at -O2 and above. You can also try -fsanitize=undefined to detect undefined behaviour at runtime.
