Messages in this thread | | | Date | Tue, 14 Apr 2009 09:45:56 +0200 | From | Martin Schwidefsky <> | Subject | Re: [PATCH] unbreak alpha percpu |
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On Fri, 10 Apr 2009 09:21:08 -0700 (PDT) Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > Hmm. I certainly personally _much_ prefer this version. > > It looks like this actually simplifies things for S390 too (no more > simple_identifier_##var games), and generally just looks better. And > seeing that the S390 special case is no longer S390-specific is also a > good sign, imho. > > Sorry for including the whole message, but I'm adding s390 and percpu > people to the cc. Guys - original uncorrupted patch on lkml. > > diff --git a/arch/s390/include/asm/percpu.h b/arch/s390/include/asm/percpu.h > > index 408d60b..6a71d73 100644 > > --- a/arch/s390/include/asm/percpu.h > > +++ b/arch/s390/include/asm/percpu.h > > @@ -13,20 +13,18 @@ > > */ > > #if defined(__s390x__) && defined(MODULE) > > > > -#define SHIFT_PERCPU_PTR(ptr,offset) (({ \ > > - extern int simple_identifier_##var(void); \ > > +#define SHIFT_PERCPU_PTR(var,offset) (({ \ > > unsigned long *__ptr; \ > > asm ( "larl %0, %1@GOTENT" \ > > - : "=a" (__ptr) : "X" (ptr) ); \ > > - (typeof(ptr))((*__ptr) + (offset)); })) > > + : "=a" (__ptr) : "X" (&per_cpu_var(var)) ); \ > > + (typeof(&per_cpu_var(var)))((*__ptr) + (offset)); })) > > > > #else > > > > -#define SHIFT_PERCPU_PTR(ptr, offset) (({ \ > > - extern int simple_identifier_##var(void); \ > > +#define SHIFT_PERCPU_PTR(var, offset) (({ \ > > unsigned long __ptr; \ > > - asm ( "" : "=a" (__ptr) : "0" (ptr) ); \ > > - (typeof(ptr)) (__ptr + (offset)); })) > > + asm ( "" : "=a" (__ptr) : "0" (&per_cpu_var(var)) ); \ > > + (typeof(&per_cpu_var(var))) (__ptr + (offset)); })) > > > > #endif > >
I would like to get rid of that SHIFT_PERCPU_PTR mess. The patch from Ivan will allow this, it uses a dummy variable to void the effect of a static modifier for percpu variables in modules. The percpu variable itself will be defined non-static, my gut feeling is that this is a dirty little trick that might bite us in the future. Another solution which I personally would prefer is to ban the use of static percpu variables. Then the compiler will use the GOT to get the address of percpu variables without any dirty tricks.
-- blue skies, Martin.
"Reality continues to ruin my life." - Calvin.
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