On Sat, Aug 17, 2019 at 09:04:42AM +0000, Christophe Leroy wrote: > Unlike BUG_ON(x), WARN_ON(x) uses !!(x) as the trigger > of the t(d/w)nei instruction instead of using directly the > value of x. > > This leads to GCC adding unnecessary pair of addic/subfe.
And it has to, it is passed as an "r" to an asm, GCC has to put the "!!" value into a register. > By using (x) instead of !!(x) like BUG_ON() does, the additional > instructions go away: But is it correct? What happens if you pass an int to WARN_ON, on a 64-bit kernel? (You might want to have 64-bit generate either tw or td. But, with your __builtin_trap patch, all that will be automatic). Segher
