#ifndef _LINUX_PERCPU_DEFS_H
  #define _LINUX_PERCPU_DEFS_H
  
  /*
   * Base implementations of per-CPU variable declarations and definitions, where
   * the section in which the variable is to be placed is provided by the
   * 'sec' argument.  This may be used to affect the parameters governing the
   * variable's storage.
   *
   * NOTE!  The sections for the DECLARE and for the DEFINE must match, lest
   * linkage errors occur due the compiler generating the wrong code to access
   * that section.
   */
  #define __PCPU_ATTRS(sec)						\
  	__percpu __attribute__((section(PER_CPU_BASE_SECTION sec)))	\
  	PER_CPU_ATTRIBUTES
  
  #define __PCPU_DUMMY_ATTRS						\
  	__attribute__((section(".discard"), unused))
  
  /*
   * Macro which verifies @ptr is a percpu pointer without evaluating
   * @ptr.  This is to be used in percpu accessors to verify that the
   * input parameter is a percpu pointer.
   *
   * + 0 is required in order to convert the pointer type from a
   * potential array type to a pointer to a single item of the array.
   */
  #define __verify_pcpu_ptr(ptr)	do {					\
  	const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;	\
  	(void)__vpp_verify;						\
  } while (0)
  
  /*
   * s390 and alpha modules require percpu variables to be defined as
   * weak to force the compiler to generate GOT based external
   * references for them.  This is necessary because percpu sections
   * will be located outside of the usually addressable area.
   *
   * This definition puts the following two extra restrictions when
   * defining percpu variables.
   *
   * 1. The symbol must be globally unique, even the static ones.
   * 2. Static percpu variables cannot be defined inside a function.
   *
   * Archs which need weak percpu definitions should define
   * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
   *
   * To ensure that the generic code observes the above two
   * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
   * definition is used for all cases.
   */
  #if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
  /*
   * __pcpu_scope_* dummy variable is used to enforce scope.  It
   * receives the static modifier when it's used in front of
   * DEFINE_PER_CPU() and will trigger build failure if
   * DECLARE_PER_CPU() is used for the same variable.
   *
   * __pcpu_unique_* dummy variable is used to enforce symbol uniqueness
   * such that hidden weak symbol collision, which will cause unrelated
   * variables to share the same address, can be detected during build.
   */
  #define DECLARE_PER_CPU_SECTION(type, name, sec)			\
  	extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;		\
  	extern __PCPU_ATTRS(sec) __typeof__(type) name
  
  #define DEFINE_PER_CPU_SECTION(type, name, sec)				\
  	__PCPU_DUMMY_ATTRS char __pcpu_scope_##name;			\
  	extern __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;		\
  	__PCPU_DUMMY_ATTRS char __pcpu_unique_##name;			\
  	extern __PCPU_ATTRS(sec) __typeof__(type) name;			\
  	__PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak			\
  	__typeof__(type) name
  #else
  /*
   * Normal declaration and definition macros.
   */
  #define DECLARE_PER_CPU_SECTION(type, name, sec)			\
  	extern __PCPU_ATTRS(sec) __typeof__(type) name
  
  #define DEFINE_PER_CPU_SECTION(type, name, sec)				\
  	__PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES			\
  	__typeof__(type) name
  #endif
  
  /*
   * Variant on the per-CPU variable declaration/definition theme used for
   * ordinary per-CPU variables.
   */
  #define DECLARE_PER_CPU(type, name)					\
  	DECLARE_PER_CPU_SECTION(type, name, "")
  
  #define DEFINE_PER_CPU(type, name)					\
  	DEFINE_PER_CPU_SECTION(type, name, "")
  
  /*
   * Declaration/definition used for per-CPU variables that must come first in
   * the set of variables.
   */
  #define DECLARE_PER_CPU_FIRST(type, name)				\
  	DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  
  #define DEFINE_PER_CPU_FIRST(type, name)				\
  	DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  
  /*
   * Declaration/definition used for per-CPU variables that must be cacheline
   * aligned under SMP conditions so that, whilst a particular instance of the
   * data corresponds to a particular CPU, inefficiencies due to direct access by
   * other CPUs are reduced by preventing the data from unnecessarily spanning
   * cachelines.
   *
   * An example of this would be statistical data, where each CPU's set of data
   * is updated by that CPU alone, but the data from across all CPUs is collated
   * by a CPU processing a read from a proc file.
   */
  #define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)			\
  	DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
  	____cacheline_aligned_in_smp
  
  #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)			\
  	DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
  	____cacheline_aligned_in_smp
  
  #define DECLARE_PER_CPU_ALIGNED(type, name)				\
  	DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)	\
  	____cacheline_aligned
  
  #define DEFINE_PER_CPU_ALIGNED(type, name)				\
  	DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)	\
  	____cacheline_aligned
  
  /*
   * Declaration/definition used for per-CPU variables that must be page aligned.
   */
  #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)			\
  	DECLARE_PER_CPU_SECTION(type, name, "..page_aligned")		\
  	__aligned(PAGE_SIZE)
  
  #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)				\
  	DEFINE_PER_CPU_SECTION(type, name, "..page_aligned")		\
  	__aligned(PAGE_SIZE)
  
  /*
   * Declaration/definition used for per-CPU variables that must be read mostly.
   */
  #define DECLARE_PER_CPU_READ_MOSTLY(type, name)			\
  	DECLARE_PER_CPU_SECTION(type, name, "..readmostly")
  
  #define DEFINE_PER_CPU_READ_MOSTLY(type, name)				\
  	DEFINE_PER_CPU_SECTION(type, name, "..readmostly")
  
  /*
   * Intermodule exports for per-CPU variables.  sparse forgets about
   * address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
   * noop if __CHECKER__.
   */
  #ifndef __CHECKER__
  #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(var)
  #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(var)
  #else
  #define EXPORT_PER_CPU_SYMBOL(var)
  #define EXPORT_PER_CPU_SYMBOL_GPL(var)
  #endif
  
  #endif /* _LINUX_PERCPU_DEFS_H */