percpu: use __weak only in the definition of weak percpu variables
[linux-2.6.git] / 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) __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 */