Re: [PATCH] unbreak alpha percpu

Al Viro
2009-04-10T15:47:19Z

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