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When CONFIG_DEBUG_FORCE_WEAK_PER_CPU or CONFIG_ARCH_NEEDS_WEAK_PER_CPU is set, DEFINE_PER_CPU() explodes into cryptic series of definitions to still allow using "static" for percpu variables while keeping all per-cpu symbols unique in the kernel image which is required for weak symbols. This ultimately converts the actual symbol to global whether DEFINE_PER_CPU() is prefixed with static or not. Unfortunately, the macro forgot to add explicit extern declartion of the actual symbol ending up defining global symbol without preceding declaration for static definitions which naturally don't have matching DECLARE_PER_CPU(). The only ill effect is triggering of the following warnings. fs/inode.c:74:8: warning: symbol 'nr_inodes' was not declared. Should it be static? fs/inode.c:75:8: warning: symbol 'nr_unused' was not declared. Should it be static? Fix it by adding extern declaration in the DEFINE_PER_CPU() macro. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Wanlong Gao <gaowanlong@cn.fujitsu.com> Tested-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
168 lines
5.9 KiB
C
168 lines
5.9 KiB
C
#ifndef _LINUX_PERCPU_DEFS_H
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#define _LINUX_PERCPU_DEFS_H
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/*
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* Base implementations of per-CPU variable declarations and definitions, where
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* the section in which the variable is to be placed is provided by the
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* 'sec' argument. This may be used to affect the parameters governing the
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* variable's storage.
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*
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* NOTE! The sections for the DECLARE and for the DEFINE must match, lest
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* linkage errors occur due the compiler generating the wrong code to access
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* that section.
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*/
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#define __PCPU_ATTRS(sec) \
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__percpu __attribute__((section(PER_CPU_BASE_SECTION sec))) \
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PER_CPU_ATTRIBUTES
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#define __PCPU_DUMMY_ATTRS \
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__attribute__((section(".discard"), unused))
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/*
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* Macro which verifies @ptr is a percpu pointer without evaluating
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* @ptr. This is to be used in percpu accessors to verify that the
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* input parameter is a percpu pointer.
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*
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* + 0 is required in order to convert the pointer type from a
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* potential array type to a pointer to a single item of the array.
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*/
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#define __verify_pcpu_ptr(ptr) do { \
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const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL; \
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(void)__vpp_verify; \
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} while (0)
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/*
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* s390 and alpha modules require percpu variables to be defined as
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* weak to force the compiler to generate GOT based external
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* references for them. This is necessary because percpu sections
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* will be located outside of the usually addressable area.
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*
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* This definition puts the following two extra restrictions when
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* defining percpu variables.
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*
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* 1. The symbol must be globally unique, even the static ones.
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* 2. Static percpu variables cannot be defined inside a function.
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*
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* Archs which need weak percpu definitions should define
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* ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
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*
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* To ensure that the generic code observes the above two
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* restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
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* definition is used for all cases.
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*/
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#if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
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/*
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* __pcpu_scope_* dummy variable is used to enforce scope. It
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* receives the static modifier when it's used in front of
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* DEFINE_PER_CPU() and will trigger build failure if
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* DECLARE_PER_CPU() is used for the same variable.
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*
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* __pcpu_unique_* dummy variable is used to enforce symbol uniqueness
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* such that hidden weak symbol collision, which will cause unrelated
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* variables to share the same address, can be detected during build.
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*/
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#define DECLARE_PER_CPU_SECTION(type, name, sec) \
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extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name; \
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extern __PCPU_ATTRS(sec) __typeof__(type) name
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#define DEFINE_PER_CPU_SECTION(type, name, sec) \
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__PCPU_DUMMY_ATTRS char __pcpu_scope_##name; \
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extern __PCPU_DUMMY_ATTRS char __pcpu_unique_##name; \
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__PCPU_DUMMY_ATTRS char __pcpu_unique_##name; \
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extern __PCPU_ATTRS(sec) __typeof__(type) name; \
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__PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak \
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__typeof__(type) name
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#else
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/*
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* Normal declaration and definition macros.
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*/
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#define DECLARE_PER_CPU_SECTION(type, name, sec) \
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extern __PCPU_ATTRS(sec) __typeof__(type) name
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#define DEFINE_PER_CPU_SECTION(type, name, sec) \
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__PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES \
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__typeof__(type) name
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#endif
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/*
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* Variant on the per-CPU variable declaration/definition theme used for
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* ordinary per-CPU variables.
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*/
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#define DECLARE_PER_CPU(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, "")
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#define DEFINE_PER_CPU(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, "")
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/*
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* Declaration/definition used for per-CPU variables that must come first in
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* the set of variables.
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*/
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#define DECLARE_PER_CPU_FIRST(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
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#define DEFINE_PER_CPU_FIRST(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
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/*
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* Declaration/definition used for per-CPU variables that must be cacheline
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* aligned under SMP conditions so that, whilst a particular instance of the
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* data corresponds to a particular CPU, inefficiencies due to direct access by
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* other CPUs are reduced by preventing the data from unnecessarily spanning
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* cachelines.
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*
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* An example of this would be statistical data, where each CPU's set of data
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* is updated by that CPU alone, but the data from across all CPUs is collated
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* by a CPU processing a read from a proc file.
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*/
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#define DECLARE_PER_CPU_SHARED_ALIGNED(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
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____cacheline_aligned_in_smp
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#define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
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____cacheline_aligned_in_smp
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#define DECLARE_PER_CPU_ALIGNED(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION) \
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____cacheline_aligned
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#define DEFINE_PER_CPU_ALIGNED(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION) \
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____cacheline_aligned
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/*
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* Declaration/definition used for per-CPU variables that must be page aligned.
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*/
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#define DECLARE_PER_CPU_PAGE_ALIGNED(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, "..page_aligned") \
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__aligned(PAGE_SIZE)
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#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, "..page_aligned") \
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__aligned(PAGE_SIZE)
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/*
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* Declaration/definition used for per-CPU variables that must be read mostly.
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*/
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#define DECLARE_PER_CPU_READ_MOSTLY(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, "..readmostly")
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#define DEFINE_PER_CPU_READ_MOSTLY(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, "..readmostly")
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/*
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* Intermodule exports for per-CPU variables. sparse forgets about
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* address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
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* noop if __CHECKER__.
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*/
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#ifndef __CHECKER__
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#define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(var)
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#define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(var)
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#else
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#define EXPORT_PER_CPU_SYMBOL(var)
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#define EXPORT_PER_CPU_SYMBOL_GPL(var)
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#endif
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#endif /* _LINUX_PERCPU_DEFS_H */
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