[PATCH] trigger a syntax error if percpu macros are incorrectly used

get_cpu_var()/per_cpu()/__get_cpu_var() arguments must be simple
identifiers.  Otherwise the arch dependent implementations might break.

This patch enforces the correct usage of the macros by producing a syntax
error if the variable is not a simple identifier.
Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-generic/percpu.h

@@ -14,7 +14,9 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
     __attribute__((__section__(".data.percpu"))) __typeof__(type) per_cpu__##name
 
 /* var is in discarded region: offset to particular copy we want */
-#define per_cpu(var, cpu) (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]))
+#define per_cpu(var, cpu) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]); }))
 #define __get_cpu_var(var) per_cpu(var, smp_processor_id())
 #define __raw_get_cpu_var(var) per_cpu(var, raw_smp_processor_id())
 

include/asm-s390/percpu.h

@@ -15,16 +15,18 @@
  */
 #if defined(__s390x__) && defined(MODULE)
 
-#define __reloc_hide(var,offset) \
-  (*({ unsigned long *__ptr; \
+#define __reloc_hide(var,offset) (*({			\
+	extern int simple_indentifier_##var(void);	\
+	unsigned long *__ptr;				\
 	asm ( "larl %0,per_cpu__"#var"@GOTENT"		\
 	    : "=a" (__ptr) : "X" (per_cpu__##var) );	\
 	(typeof(&per_cpu__##var))((*__ptr) + (offset));	}))
 
 #else
 
-#define __reloc_hide(var, offset) \
-  (*({ unsigned long __ptr; \
+#define __reloc_hide(var, offset) (*({				\
+	extern int simple_indentifier_##var(void);		\
+	unsigned long __ptr;					\
 	asm ( "" : "=a" (__ptr) : "0" (&per_cpu__##var) );	\
 	(typeof(&per_cpu__##var)) (__ptr + (offset)); }))
 

include/asm-x86_64/percpu.h

@@ -21,9 +21,15 @@
     __attribute__((__section__(".data.percpu"))) __typeof__(type) per_cpu__##name
 
 /* var is in discarded region: offset to particular copy we want */
-#define per_cpu(var, cpu) (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset(cpu)))
-#define __get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()))
-#define __raw_get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()))
+#define per_cpu(var, cpu) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	RELOC_HIDE(&per_cpu__##var, __per_cpu_offset(cpu)); }))
+#define __get_cpu_var(var) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()); }))
+#define __raw_get_cpu_var(var) (*({			\
+	extern int simple_indentifier_##var(void);	\
+	RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()); }))
 
 /* A macro to avoid #include hell... */
 #define percpu_modcopy(pcpudst, src, size)			\

include/linux/percpu.h

@@ -11,8 +11,14 @@
 #define PERCPU_ENOUGH_ROOM 32768
 #endif
 
-/* Must be an lvalue. */
-#define get_cpu_var(var) (*({ preempt_disable(); &__get_cpu_var(var); }))
+/*
+ * Must be an lvalue. Since @var must be a simple identifier,
+ * we force a syntax error here if it isn't.
+ */
+#define get_cpu_var(var) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	preempt_disable();				\
+	&__get_cpu_var(var); }))
 #define put_cpu_var(var) preempt_enable()
 
 #ifdef CONFIG_SMP