On 15:38 Mon 16 May , Arnaud Lacombe wrote: > Hi, > > On Mon, May 16, 2011 at 3:03 PM, <Valdis.Kletnieks@xxxxxx> wrote: > > On Fri, 13 May 2011 10:09:09 +0200, Jean-Christophe PLAGNIOL-VILLARD said: > >> On 10:52 Mon 09 May , Michal Marek wrote: > >> > Do you have proof of concept patches that make use of the > >> > config_is_xxx macros? Acked by the respective subsystem maintainers? > >> > It would be a good idea to send them along to show that this feature > >> > is going to be actually used. > >> I've seen thousands of place in the kernel we can use > >> so I'll just take one example on x86 > >> > >> the patch attached is just an example > > > > Out of curiosity, will this Do The Right Thing for cases where things simply won't > > build for some configs? For example, consider this code snippet from kernel/timer.c, > > in __mod_timer() (near line 682): > > > > debug_activate(timer, expires); > > > > cpu = smp_processor_id(); > > > > #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP) > > if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu)) > > cpu = get_nohz_timer_target(); > > #endif > > new_base = per_cpu(tvec_bases, cpu); > > > > If you convert this to an if statement, will it still compile? Which will > > happen first, dead code elimination, or the warning that get_nohz_timer_target() > > is an implicit declaration because the definition in the .h file is also > > guarded by #ifdef CONFIG_NO_HZ? > > > I already exposed this case, but let's prove it: > > % grep CONFIG_SMP .config > # CONFIG_SMP is not set > > % git diff > diff --git a/kernel/timer.c b/kernel/timer.c > index fd61986..ea4a5ba 100644 > --- a/kernel/timer.c > +++ b/kernel/timer.c > @@ -681,10 +681,8 @@ __mod_timer(struct timer_list *timer, unsigned > long expires, > > cpu = smp_processor_id(); > > -#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP) > - if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu)) > + if (0 && 0 && !pinned && get_sysctl_timer_migration() && idle_cpu(cpu)) > cpu = get_nohz_timer_target(); > -#endif > new_base = per_cpu(tvec_bases, cpu); > > % gmake kernel/timer.o > CHK include/linux/version.h > CHK include/generated/utsrelease.h > CALL scripts/checksyscalls.sh > CC kernel/timer.o > kernel/timer.c: In function '__mod_timer': > kernel/timer.c:685:3: error: implicit declaration of function > 'get_nohz_timer_target' > gmake[1]: *** [kernel/timer.o] Error 1 > gmake: *** [kernel/timer.o] Error 2 because we do not define the inline function if the CONFIG_ is not define as we are supposed to do if we want to compile without ifdef everywhere Best Regards, J. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
