include/linux/percpu-defs.h

   1 #ifndef _LINUX_PERCPU_DEFS_H
   2 #define _LINUX_PERCPU_DEFS_H
   3
   4 /*
   5  * Base implementations of per-CPU variable declarations and definitions, where
   6  * the section in which the variable is to be placed is provided by the
   7  * 'sec' argument.  This may be used to affect the parameters governing the
   8  * variable's storage.
   9  *
  10  * NOTE!  The sections for the DECLARE and for the DEFINE must match, lest
  11  * linkage errors occur due the compiler generating the wrong code to access
  12  * that section.
  13  */
  14 #define __PCPU_ATTRS(sec)                                               \
  15         __percpu __attribute__((section(PER_CPU_BASE_SECTION sec)))     \
  16         PER_CPU_ATTRIBUTES
  17
  18 #define __PCPU_DUMMY_ATTRS                                              \
  19         __attribute__((section(".discard"), unused))
  20
  21 /*
  22  * Macro which verifies @ptr is a percpu pointer without evaluating
  23  * @ptr.  This is to be used in percpu accessors to verify that the
  24  * input parameter is a percpu pointer.
  25  */
  26 #define __verify_pcpu_ptr(ptr)  do {                                    \
  27         const void __percpu *__vpp_verify = (typeof(ptr))NULL;          \
  28         (void)__vpp_verify;                                             \
  29 } while (0)
  30
  31 /*
  32  * s390 and alpha modules require percpu variables to be defined as
  33  * weak to force the compiler to generate GOT based external
  34  * references for them.  This is necessary because percpu sections
  35  * will be located outside of the usually addressable area.
  36  *
  37  * This definition puts the following two extra restrictions when
  38  * defining percpu variables.
  39  *
  40  * 1. The symbol must be globally unique, even the static ones.
  41  * 2. Static percpu variables cannot be defined inside a function.
  42  *
  43  * Archs which need weak percpu definitions should define
  44  * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
  45  *
  46  * To ensure that the generic code observes the above two
  47  * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
  48  * definition is used for all cases.
  49  */
  50 #if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
  51 /*
  52  * __pcpu_scope_* dummy variable is used to enforce scope.  It
  53  * receives the static modifier when it's used in front of
  54  * DEFINE_PER_CPU() and will trigger build failure if
  55  * DECLARE_PER_CPU() is used for the same variable.
  56  *
  57  * __pcpu_unique_* dummy variable is used to enforce symbol uniqueness
  58  * such that hidden weak symbol collision, which will cause unrelated
  59  * variables to share the same address, can be detected during build.
  60  */
  61 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  62         extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;             \
  63         extern __PCPU_ATTRS(sec) __typeof__(type) name
  64
  65 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  66         __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;                    \
  67         extern __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;            \
  68         __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;                   \
  69         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak                 \
  70         __typeof__(type) name
  71 #else
  72 /*
  73  * Normal declaration and definition macros.
  74  */
  75 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  76         extern __PCPU_ATTRS(sec) __typeof__(type) name
  77
  78 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  79         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES                        \
  80         __typeof__(type) name
  81 #endif
  82
  83 /*
  84  * Variant on the per-CPU variable declaration/definition theme used for
  85  * ordinary per-CPU variables.
  86  */
  87 #define DECLARE_PER_CPU(type, name)                                     \
  88         DECLARE_PER_CPU_SECTION(type, name, "")
  89
  90 #define DEFINE_PER_CPU(type, name)                                      \
  91         DEFINE_PER_CPU_SECTION(type, name, "")
  92
  93 /*
  94  * Declaration/definition used for per-CPU variables that must come first in
  95  * the set of variables.
  96  */
  97 #define DECLARE_PER_CPU_FIRST(type, name)                               \
  98         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  99
 100 #define DEFINE_PER_CPU_FIRST(type, name)                                \
 101         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
 102
 103 /*
 104  * Declaration/definition used for per-CPU variables that must be cacheline
 105  * aligned under SMP conditions so that, whilst a particular instance of the
 106  * data corresponds to a particular CPU, inefficiencies due to direct access by
 107  * other CPUs are reduced by preventing the data from unnecessarily spanning
 108  * cachelines.
 109  *
 110  * An example of this would be statistical data, where each CPU's set of data
 111  * is updated by that CPU alone, but the data from across all CPUs is collated
 112  * by a CPU processing a read from a proc file.
 113  */
 114 #define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)                      \
 115         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 116         ____cacheline_aligned_in_smp
 117
 118 #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
 119         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 120         ____cacheline_aligned_in_smp
 121
 122 #define DECLARE_PER_CPU_ALIGNED(type, name)                             \
 123         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)    \
 124         ____cacheline_aligned
 125
 126 #define DEFINE_PER_CPU_ALIGNED(type, name)                              \
 127         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)     \
 128         ____cacheline_aligned
 129
 130 /*
 131  * Declaration/definition used for per-CPU variables that must be page aligned.
 132  */
 133 #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)                        \
 134         DECLARE_PER_CPU_SECTION(type, name, "..page_aligned")           \
 135         __aligned(PAGE_SIZE)
 136
 137 #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)                         \
 138         DEFINE_PER_CPU_SECTION(type, name, "..page_aligned")            \
 139         __aligned(PAGE_SIZE)
 140
 141 /*
 142  * Declaration/definition used for per-CPU variables that must be read mostly.
 143  */
 144 #define DECLARE_PER_CPU_READ_MOSTLY(type, name)                 \
 145         DECLARE_PER_CPU_SECTION(type, name, "..readmostly")
 146
 147 #define DEFINE_PER_CPU_READ_MOSTLY(type, name)                          \
 148         DEFINE_PER_CPU_SECTION(type, name, "..readmostly")
 149
 150 /*
 151  * Intermodule exports for per-CPU variables.  sparse forgets about
 152  * address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
 153  * noop if __CHECKER__.
 154  */
 155 #ifndef __CHECKER__
 156 #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(var)
 157 #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(var)
 158 #else
 159 #define EXPORT_PER_CPU_SYMBOL(var)
 160 #define EXPORT_PER_CPU_SYMBOL_GPL(var)
 161 #endif
 162
 163 #endif /* _LINUX_PERCPU_DEFS_H */