export.h

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#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H
/*
 * Export symbols from the kernel to modules.  Forked from module.h
 * to reduce the amount of pointless cruft we feed to gcc when only
 * exporting a simple symbol or two.
 *
 * If you feel the need to add #include <linux/foo.h> to this file
 * then you are doing something wrong and should go away silently.
 */

/* Some toolchains use a `_' prefix for all user symbols. */
#ifdef CONFIG_SYMBOL_PREFIX
#define MODULE_SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
#else
#define MODULE_SYMBOL_PREFIX ""
#endif

struct kernel_symbol
{
    unsigned long value;
    const char *name;
};

#ifdef MODULE
extern struct module __this_module;
#define THIS_MODULE (&__this_module)
#else
#define THIS_MODULE ((struct module *)0)
#endif

#ifdef CONFIG_MODULES

#ifndef __GENKSYMS__
#ifdef CONFIG_MODVERSIONS
/* Mark the CRC weak since genksyms apparently decides not to
 * generate a checksums for some symbols */
#define __CRC_SYMBOL(sym, sec)                  \
    extern void *__crc_##sym __attribute__((weak));     \
    static const unsigned long __kcrctab_##sym      \
    __used                          \
    __attribute__((section("___kcrctab" sec "+" #sym), unused)) \
    = (unsigned long) &__crc_##sym;
#else
#define __CRC_SYMBOL(sym, sec)
#endif

/* For every exported symbol, place a struct in the __ksymtab section */
#define __EXPORT_SYMBOL(sym, sec)               \
    extern typeof(sym) sym;                 \
    __CRC_SYMBOL(sym, sec)                  \
    static const char __kstrtab_##sym[]         \
    __attribute__((section("__ksymtab_strings"), aligned(1))) \
    = MODULE_SYMBOL_PREFIX #sym;                \
    static const struct kernel_symbol __ksymtab_##sym   \
    __used                          \
    __attribute__((section("___ksymtab" sec "+" #sym), unused)) \
    = { (unsigned long)&sym, __kstrtab_##sym }

#define EXPORT_SYMBOL(sym)                  \
    __EXPORT_SYMBOL(sym, "")

#define EXPORT_SYMBOL_GPL(sym)                  \
    __EXPORT_SYMBOL(sym, "_gpl")

#define EXPORT_SYMBOL_GPL_FUTURE(sym)               \
    __EXPORT_SYMBOL(sym, "_gpl_future")

#ifdef CONFIG_UNUSED_SYMBOLS
#define EXPORT_UNUSED_SYMBOL(sym) __EXPORT_SYMBOL(sym, "_unused")
#define EXPORT_UNUSED_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_unused_gpl")
#else
#define EXPORT_UNUSED_SYMBOL(sym)
#define EXPORT_UNUSED_SYMBOL_GPL(sym)
#endif

#endif  /* __GENKSYMS__ */

#else /* !CONFIG_MODULES... */

#define EXPORT_SYMBOL(sym)
#define EXPORT_SYMBOL_GPL(sym)
#define EXPORT_SYMBOL_GPL_FUTURE(sym)
#define EXPORT_UNUSED_SYMBOL(sym)
#define EXPORT_UNUSED_SYMBOL_GPL(sym)

#endif /* CONFIG_MODULES */

#endif /* _LINUX_EXPORT_H */