Re: [PATCH] unbreak alpha percpu

[Linus Torvalds <torvalds@linux-foundation.org>]

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.

		Linus

---
On Fri, 10 Apr 2009, Al Viro wrote:
> On Fri, Apr 10, 2009 at 04:12:24PM +0100, Al Viro wrote:
> > asm-generic/percpu.h is *NOT* included by every asm/percpu.h out there.
> > Namely, alpha can't use it since it needs the var name in
> > SHIFT_PERCPU_PTR - &per_cpu_var(var) won't do at all.  So adding stuff
> > to asm-generic/percpu.h and expecting it to be picked by everything
> > is not going to work.
> > 
> > Frankly, I'd rather have SHIFT_PERCPU_PTR() calling conventions changed,
> > but for now the patch below will do.
> > 
> > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> 
> Alternative patch (changing SHIFT_PERCPU_PTR() arguments and switching
> alpha to asm-generic/percpu.h) would be this (only build-tested, though):
> 
> diff --git a/arch/alpha/include/asm/percpu.h b/arch/alpha/include/asm/percpu.h
> index 3495e8e..1c52a2d 100644
> --- a/arch/alpha/include/asm/percpu.h
> +++ b/arch/alpha/include/asm/percpu.h
> @@ -3,33 +3,8 @@
>  #include <linux/compiler.h>
>  #include <linux/threads.h>
>  
> -/*
> - * Determine the real variable name from the name visible in the
> - * kernel sources.
> - */
> -#define per_cpu_var(var) per_cpu__##var
> -
>  #ifdef CONFIG_SMP
> -
> -/*
> - * per_cpu_offset() is the offset that has to be added to a
> - * percpu variable to get to the instance for a certain processor.
> - */
> -extern unsigned long __per_cpu_offset[NR_CPUS];
> -
> -#define per_cpu_offset(x) (__per_cpu_offset[x])
> -
> -#define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
> -#ifdef CONFIG_DEBUG_PREEMPT
> -#define my_cpu_offset per_cpu_offset(smp_processor_id())
> -#else
> -#define my_cpu_offset __my_cpu_offset
> -#endif
> -
> -#ifndef MODULE
> -#define SHIFT_PERCPU_PTR(var, offset) RELOC_HIDE(&per_cpu_var(var), (offset))
> -#define PER_CPU_ATTRIBUTES
> -#else
> +#ifdef MODULE
>  /*
>   * To calculate addresses of locally defined variables, GCC uses 32-bit
>   * displacement from the GP. Which doesn't work for per cpu variables in
> @@ -39,40 +14,15 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
>   * ldq instruction with a 'literal' relocation.
>   */
>  #define SHIFT_PERCPU_PTR(var, offset) ({		\
> -	extern int simple_identifier_##var(void);	\
>  	unsigned long __ptr, tmp_gp;			\
>  	asm (  "br	%1, 1f		  	      \n\
>  	1:	ldgp	%1, 0(%1)	    	      \n\
>  		ldq %0, per_cpu__" #var"(%1)\t!literal"		\
>  		: "=&r"(__ptr), "=&r"(tmp_gp));		\
>  	(typeof(&per_cpu_var(var)))(__ptr + (offset)); })
> -
> -#define PER_CPU_ATTRIBUTES	__used
> -
>  #endif /* MODULE */
> -
> -/*
> - * A percpu variable may point to a discarded regions. The following are
> - * established ways to produce a usable pointer from the percpu variable
> - * offset.
> - */
> -#define per_cpu(var, cpu) \
> -	(*SHIFT_PERCPU_PTR(var, per_cpu_offset(cpu)))
> -#define __get_cpu_var(var) \
> -	(*SHIFT_PERCPU_PTR(var, my_cpu_offset))
> -#define __raw_get_cpu_var(var) \
> -	(*SHIFT_PERCPU_PTR(var, __my_cpu_offset))
> -
> -#else /* ! SMP */
> -
> -#define per_cpu(var, cpu)		(*((void)(cpu), &per_cpu_var(var)))
> -#define __get_cpu_var(var)		per_cpu_var(var)
> -#define __raw_get_cpu_var(var)		per_cpu_var(var)
> -
> -#define PER_CPU_ATTRIBUTES
> -
>  #endif /* SMP */
>  
> -#define DECLARE_PER_CPU(type, name) extern __typeof__(type) per_cpu_var(name)
> +#include <asm-generic/percpu.h>
>  
>  #endif /* __ALPHA_PERCPU_H */
> 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
>  
> diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
> index 00f45ff..7463700 100644
> --- a/include/asm-generic/percpu.h
> +++ b/include/asm-generic/percpu.h
> @@ -42,10 +42,10 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
>  /*
>   * Add a offset to a pointer but keep the pointer as is.
>   *
> - * Only S390 provides its own means of moving the pointer.
> + * Only S390 and Alpha provide their own means of moving the pointer.
>   */
>  #ifndef SHIFT_PERCPU_PTR
> -#define SHIFT_PERCPU_PTR(__p, __offset)	RELOC_HIDE((__p), (__offset))
> +#define SHIFT_PERCPU_PTR(__v, __offset)	RELOC_HIDE(&per_cpu_var(__v), (__offset))
>  #endif
>  
>  /*
> @@ -54,11 +54,11 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
>   * offset.
>   */
>  #define per_cpu(var, cpu) \
> -	(*SHIFT_PERCPU_PTR(&per_cpu_var(var), per_cpu_offset(cpu)))
> +	(*SHIFT_PERCPU_PTR(var, per_cpu_offset(cpu)))
>  #define __get_cpu_var(var) \
> -	(*SHIFT_PERCPU_PTR(&per_cpu_var(var), my_cpu_offset))
> +	(*SHIFT_PERCPU_PTR(var, my_cpu_offset))
>  #define __raw_get_cpu_var(var) \
> -	(*SHIFT_PERCPU_PTR(&per_cpu_var(var), __my_cpu_offset))
> +	(*SHIFT_PERCPU_PTR(var, __my_cpu_offset))
>  
>  
>  #ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
>