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