On Mon, Apr 16, 2018 at 10:54:26AM +0200, Philipp Klocke wrote:

This patch is motivated by the clang warning Wconstant-logical-operand, issued when logically comparing a variable to a constant integer that is neither 1 nor 0. It happens for sched_feat(x) when sysctl_sched_features is constant, i.e., CONFIG_SCHED_DEBUG is not set.

kernel/sched/fair.c:3927:14: warning: use of logical '&&' with constant operand [-Wconstant-logical-operand] if (initial && sched_feat(START_DEBIT)) ^ ~~~~~~~~~~~~~~~~~~~~~~~ kernel/sched/fair.c:3927:14: note: use '&' for a bitwise operation if (initial && sched_feat(START_DEBIT)) ^~ & kernel/sched/fair.c:3927:14: note: remove constant to silence this warning if (initial && sched_feat(START_DEBIT)) ~^~~~~~~~~~~~~~~~~~~~~~~~~~

@@ -1305,7 +1305,11 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features = 0; #undef SCHED_FEAT

+#ifdef CONFIG_SCHED_DEBUG #define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x)) +#else +#define sched_feat(x) ((sysctl_sched_features >> __SCHED_FEAT_##x) & 1UL) +#endif

So this is extra ugly, for no gain? WTH does clang complain about a constant? Can't you just disable that stupid warning? Also, if sysctl_sched_features is a constant, the both expressions _should_ really result in a constant and clang should still warn about it. I'm really not seeing why we'd want to do this. Just fix clang to not be stupid.