On Thu, Mar 25, 2021 at 01:42:41AM +0100, Rasmus Villemoes wrote: > > Actually, it looks like I can't select PREEMPT_DYNAMIC> and tweaking Kconfig > > Ah, there's no prompt on the "bool" line, so it doesn't show up. That > seems to be a mistake, since there's an elaborate help text which says > > The runtime overhead is negligible with > HAVE_STATIC_CALL_INLINE enabled > but if runtime patching is not available for the specific > architecture > then the potential overhead should be considered. > > So it seems that it was meant to be "you can enable this if you really > want". > > to force enable it on arm64 results in a build error
Right, PREEMPT_DYNAMIC really hard relies on HAVE_STATIC_CALL There's an implicit dependency in the select: config PREEMPT ... select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC > > ("implicit declaration of function 'static_call_mod'"). > > Seems to be an omission in the last !HAVE_STATIC_CALL branch in > static_call_types.h, and there's also no > EXPORT_STATIC_CALL_TRAMP{,_GPL} in static_call.h for that case. That interface doesn't make sense for !HAVE_STATIC_CALL. It's impossible to not export the function pointer itself but still call it for !HAVE_STATIC_CALL.