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         extern __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;            \
  64         __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;                   \
  65         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak                 \
  66         __typeof__(type) per_cpu__##name
  67 #else
  68 /*
  69  * Normal declaration and definition macros.
  70  */
  71 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  72         extern __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name
  73
  74 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  75         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES                        \
  76         __typeof__(type) per_cpu__##name
  77 #endif
  78
  79 /*
  80  * Variant on the per-CPU variable declaration/definition theme used for
  81  * ordinary per-CPU variables.
  82  */
  83 #define DECLARE_PER_CPU(type, name)                                     \
  84         DECLARE_PER_CPU_SECTION(type, name, "")
  85
  86 #define DEFINE_PER_CPU(type, name)                                      \
  87         DEFINE_PER_CPU_SECTION(type, name, "")
  88
  89 /*
  90  * Declaration/definition used for per-CPU variables that must come first in
  91  * the set of variables.
  92  */
  93 #define DECLARE_PER_CPU_FIRST(type, name)                               \
  94         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  95
  96 #define DEFINE_PER_CPU_FIRST(type, name)                                \
  97         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  98
  99 /*
 100  * Declaration/definition used for per-CPU variables that must be cacheline
 101  * aligned under SMP conditions so that, whilst a particular instance of the
 102  * data corresponds to a particular CPU, inefficiencies due to direct access by
 103  * other CPUs are reduced by preventing the data from unnecessarily spanning
 104  * cachelines.
 105  *
 106  * An example of this would be statistical data, where each CPU's set of data
 107  * is updated by that CPU alone, but the data from across all CPUs is collated
 108  * by a CPU processing a read from a proc file.
 109  */
 110 #define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)                      \
 111         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 112         ____cacheline_aligned_in_smp
 113
 114 #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
 115         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 116         ____cacheline_aligned_in_smp
 117
 118 #define DECLARE_PER_CPU_ALIGNED(type, name)                             \
 119         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)    \
 120         ____cacheline_aligned
 121
 122 #define DEFINE_PER_CPU_ALIGNED(type, name)                              \
 123         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)     \
 124         ____cacheline_aligned
 125
 126 /*
 127  * Declaration/definition used for per-CPU variables that must be page aligned.
 128  */
 129 #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)                        \
 130         DECLARE_PER_CPU_SECTION(type, name, ".page_aligned")            \
 131         __aligned(PAGE_SIZE)
 132
 133 #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)                         \
 134         DEFINE_PER_CPU_SECTION(type, name, ".page_aligned")             \
 135         __aligned(PAGE_SIZE)
 136
 137 /*
 138  * Intermodule exports for per-CPU variables.
 139  */
 140 #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var)
 141 #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var)
 142
 143
 144 #endif /* _LINUX_PERCPU_DEFS_H */