On Tue, Oct 01, 2019 at 04:28:27PM +0100, Andrew Murray wrote: > I hadn't noticed the use of __OPTIMIZE__ - indeed if __compiletime_assert > is no-op'd and you reach it then you won't have a build error - but you > may get uninitialised values instead. > > Presumably the purpose of __OPTIMIZE__ in this case is to prevent getting > an undefined function error for the __compiletime_assert line, even though > it doesn't get called (when using a compiler that doesn't optimize out the > call to the unused function). > > Why is the call to __get_user_bad not guarded in this way for when > __OPTIMIZE__ isn't set, i.e. why doesn't it suffer from the issue > that the following fixes?
Officially, the kernel does not support building with -O0. To start with, the top level makefile has: ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os else KBUILD_CFLAGS += -O2 endif and we've said for years that the kernel relies upon the compiler optimiser to build correctly. You may be lucky if you pass it via some method to 'make' but that's going to rely on the argument order to the compiler, and the order in which the compiler processes its arguments, and whether it (for example) correctly disables all optimisations if it encounters -O0 somewhere. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up