include/linux/percpu-defs.h

   1 #ifndef _LINUX_PERCPU_DEFS_H
   2 #define _LINUX_PERCPU_DEFS_H
   3
   4 /*
   5  * Determine the real variable name from the name visible in the
   6  * kernel sources.
   7  */
   8 #define per_cpu_var(var) per_cpu__##var
   9
  10 /*
  11  * Base implementations of per-CPU variable declarations and definitions, where
  12  * the section in which the variable is to be placed is provided by the
  13  * 'sec' argument.  This may be used to affect the parameters governing the
  14  * variable's storage.
  15  *
  16  * NOTE!  The sections for the DECLARE and for the DEFINE must match, lest
  17  * linkage errors occur due the compiler generating the wrong code to access
  18  * that section.
  19  */
  20 #define __PCPU_ATTRS(sec)                                               \
  21         __attribute__((section(PER_CPU_BASE_SECTION sec)))              \
  22         PER_CPU_ATTRIBUTES
  23
  24 #define __PCPU_DUMMY_ATTRS                                              \
  25         __attribute__((section(".discard"), unused))
  26
  27 /*
  28  * s390 and alpha modules require percpu variables to be defined as
  29  * weak to force the compiler to generate GOT based external
  30  * references for them.  This is necessary because percpu sections
  31  * will be located outside of the usually addressable area.
  32  *
  33  * This definition puts the following two extra restrictions when
  34  * defining percpu variables.
  35  *
  36  * 1. The symbol must be globally unique, even the static ones.
  37  * 2. Static percpu variables cannot be defined inside a function.
  38  *
  39  * Archs which need weak percpu definitions should define
  40  * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
  41  *
  42  * To ensure that the generic code observes the above two
  43  * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
  44  * definition is used for all cases.
  45  */
  46 #if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
  47 /*
  48  * __pcpu_scope_* dummy variable is used to enforce scope.  It
  49  * receives the static modifier when it's used in front of
  50  * DEFINE_PER_CPU() and will trigger build failure if
  51  * DECLARE_PER_CPU() is used for the same variable.
  52  *
  53  * __pcpu_unique_* dummy variable is used to enforce symbol uniqueness
  54  * such that hidden weak symbol collision, which will cause unrelated
  55  * variables to share the same address, can be detected during build.
  56  */
  57 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  58         extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;             \
  59         extern __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name
  60
  61 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  62         __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;                    \
  63         __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;                   \
  64         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak                 \
  65         __typeof__(type) per_cpu__##name
  66 #else
  67 /*
  68  * Normal declaration and definition macros.
  69  */
  70 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  71         extern __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name
  72
  73 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  74         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES                        \
  75         __typeof__(type) per_cpu__##name
  76 #endif
  77
  78 /*
  79  * Variant on the per-CPU variable declaration/definition theme used for
  80  * ordinary per-CPU variables.
  81  */
  82 #define DECLARE_PER_CPU(type, name)                                     \
  83         DECLARE_PER_CPU_SECTION(type, name, "")
  84
  85 #define DEFINE_PER_CPU(type, name)                                      \
  86         DEFINE_PER_CPU_SECTION(type, name, "")
  87
  88 /*
  89  * Declaration/definition used for per-CPU variables that must come first in
  90  * the set of variables.
  91  */
  92 #define DECLARE_PER_CPU_FIRST(type, name)                               \
  93         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  94
  95 #define DEFINE_PER_CPU_FIRST(type, name)                                \
  96         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  97
  98 /*
  99  * Declaration/definition used for per-CPU variables that must be cacheline
 100  * aligned under SMP conditions so that, whilst a particular instance of the
 101  * data corresponds to a particular CPU, inefficiencies due to direct access by
 102  * other CPUs are reduced by preventing the data from unnecessarily spanning
 103  * cachelines.
 104  *
 105  * An example of this would be statistical data, where each CPU's set of data
 106  * is updated by that CPU alone, but the data from across all CPUs is collated
 107  * by a CPU processing a read from a proc file.
 108  */
 109 #define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)                      \
 110         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 111         ____cacheline_aligned_in_smp
 112
 113 #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
 114         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 115         ____cacheline_aligned_in_smp
 116
 117 #define DECLARE_PER_CPU_ALIGNED(type, name)                             \
 118         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)    \
 119         ____cacheline_aligned
 120
 121 #define DEFINE_PER_CPU_ALIGNED(type, name)                              \
 122         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)     \
 123         ____cacheline_aligned
 124
 125 /*
 126  * Declaration/definition used for per-CPU variables that must be page aligned.
 127  */
 128 #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)                        \
 129         DECLARE_PER_CPU_SECTION(type, name, ".page_aligned")            \
 130         __aligned(PAGE_SIZE)
 131
 132 #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)                         \
 133         DEFINE_PER_CPU_SECTION(type, name, ".page_aligned")             \
 134         __aligned(PAGE_SIZE)
 135
 136 /*
 137  * Intermodule exports for per-CPU variables.
 138  */
 139 #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var)
 140 #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var)
 141
 142
 143 #endif /* _LINUX_PERCPU_DEFS_H */