On Sat, Dec 12, 2020 at 12:07 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Fri, Dec 11 2020 at 22:08, Thomas Gleixner wrote: > > > On Fri, Dec 11 2020 at 19:53, Andy Shevchenko wrote: > > > >> On Thu, Dec 10, 2020 at 10:14 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >>> > >>> irq_set_lockdep_class() is used from modules and requires irq_to_desc() to > >>> be exported. Move it into the core code which lifts another requirement for > >>> the export. > >> > >> ... > >> > >>> + if (IS_ENABLED(CONFIG_LOCKDEP)) > >>> + __irq_set_lockdep_class(irq, lock_class, request_class); > > > > You are right. Let me fix that. > > No. I have to correct myself. You're wrong. > > The inline is evaluated in the compilation units which include that > header and because the function declaration is unconditional it is > happy. > > Now the optimizer stage makes the whole thing a NOOP if CONFIG_LOCKDEP=n > and thereby drops the reference to the function which makes it not > required for linking. > > So in the file where the function is implemented: > > #ifdef CONFIG_LOCKDEP > void __irq_set_lockdep_class(....) > { > } > #endif > > The whole block is either discarded because CONFIG_LOCKDEP is not > defined or compile if it is defined which makes it available for the > linker. > > And in the latter case the optimizer keeps the call in the inline (it > optimizes the condition away because it's always true). > > So in both cases the compiler and the linker are happy and everything > works as expected. > > It would fail if the header file had the following: > > #ifdef CONFIG_LOCKDEP > void __irq_set_lockdep_class(....); > #endif > > Because then it would complain about the missing function prototype when > it evaluates the inline. I understand that (that's why I put "if even no warning") and what I'm talking about is the purpose of IS_ENABLED(). It's usually good for compile testing !CONFIG_FOO cases. But here it seems inconsistent. The pattern I usually see in the cases like this is #ifdef CONFIG_LOCKDEP void __irq_set_lockdep_class(....); #else static inline void ... {} #endif and call it directly in the caller. It's not a big deal, so up to you. -- With Best Regards, Andy Shevchenko _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel