include/linux/export.h

#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.
 *
 * Try not to add #includes here.  It slows compilation and makes kernel
 * hackers place grumpy comments in header files.
 */

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

#define NS_SEPARATOR "."

#ifdef CONFIG_MODVERSIONS
/* Mark the CRC weak since genksyms apparently decides not to
 * generate a checksums for some symbols */
#if defined(CONFIG_MODULE_REL_CRCS)
#define __CRC_SYMBOL(sym, sec)						\
	asm("	.section \"___kcrctab" sec "+" #sym "\", \"a\"	\n"	\
	    "	.weak	__crc_" #sym "				\n"	\
	    "	.long	__crc_" #sym " - .			\n"	\
	    "	.previous					\n")
#else
#define __CRC_SYMBOL(sym, sec)						\
	asm("	.section \"___kcrctab" sec "+" #sym "\", \"a\"	\n"	\
	    "	.weak	__crc_" #sym "				\n"	\
	    "	.long	__crc_" #sym "				\n"	\
	    "	.previous					\n")
#endif
#else
#define __CRC_SYMBOL(sym, sec)
#endif

#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
#include <linux/compiler.h>
/*
 * Emit the ksymtab entry as a pair of relative references: this reduces
 * the size by half on 64-bit architectures, and eliminates the need for
 * absolute relocations that require runtime processing on relocatable
 * kernels.
 */
#define __KSYMTAB_ENTRY_NS(sym, sec, ns)				\
	__ADDRESSABLE(sym)						\
	asm("	.section \"___ksymtab" sec "+" #sym "\", \"a\"	\n"	\
	    "	.balign	4					\n"	\
	    "__ksymtab_" #ns NS_SEPARATOR #sym ":		\n"	\
	    "	.long	" #sym "- .				\n"	\
	    "	.long	__kstrtab_" #sym "- .			\n"	\
	    "	.long	__kstrtabns_" #sym "- .			\n"	\
	    "	.previous					\n")

#define __KSYMTAB_ENTRY(sym, sec)					\
	__ADDRESSABLE(sym)						\
	asm("	.section \"___ksymtab" sec "+" #sym "\", \"a\"	\n"	\
	    "	.balign 4					\n"	\
	    "__ksymtab_" #sym ":				\n"	\
	    "	.long	" #sym "- .				\n"	\
	    "	.long	__kstrtab_" #sym "- .			\n"	\
	    "	.long	0					\n"	\
	    "	.previous					\n")

struct kernel_symbol {
	int value_offset;
	int name_offset;
	int namespace_offset;
};
#else
#define __KSYMTAB_ENTRY_NS(sym, sec, ns)				\
	static const struct kernel_symbol __ksymtab_##sym##__##ns	\
	asm("__ksymtab_" #ns NS_SEPARATOR #sym)				\
	__attribute__((section("___ksymtab" sec "+" #sym), used))	\
	__aligned(sizeof(void *))					\
	= { (unsigned long)&sym, __kstrtab_##sym, __kstrtabns_##sym }

#define __KSYMTAB_ENTRY(sym, sec)					\
	static const struct kernel_symbol __ksymtab_##sym		\
	asm("__ksymtab_" #sym)						\
	__attribute__((section("___ksymtab" sec "+" #sym), used))	\
	__aligned(sizeof(void *))					\
	= { (unsigned long)&sym, __kstrtab_##sym, NULL }

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

#ifdef __GENKSYMS__

#define ___EXPORT_SYMBOL(sym,sec)	__GENKSYMS_EXPORT_SYMBOL(sym)
#define ___EXPORT_SYMBOL_NS(sym,sec,ns)	__GENKSYMS_EXPORT_SYMBOL(sym)

#else

#define ___export_symbol_common(sym, sec)				\
	extern typeof(sym) sym;						\
	__CRC_SYMBOL(sym, sec);						\
	static const char __kstrtab_##sym[]				\
	__attribute__((section("__ksymtab_strings"), used, aligned(1)))	\
	= #sym								\

/* For every exported symbol, place a struct in the __ksymtab section */
#define ___EXPORT_SYMBOL_NS(sym, sec, ns)				\
	___export_symbol_common(sym, sec);				\
	static const char __kstrtabns_##sym[]				\
	__attribute__((section("__ksymtab_strings"), used, aligned(1)))	\
	= #ns;								\
	__KSYMTAB_ENTRY_NS(sym, sec, ns)

#define ___EXPORT_SYMBOL(sym, sec)					\
	___export_symbol_common(sym, sec);				\
	__KSYMTAB_ENTRY(sym, sec)

#endif

#if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)

/*
 * Allow symbol exports to be disabled completely so that C code may
 * be reused in other execution contexts such as the UEFI stub or the
 * decompressor.
 */
#define __EXPORT_SYMBOL_NS(sym, sec, ns)
#define __EXPORT_SYMBOL(sym, sec)

#elif defined(CONFIG_TRIM_UNUSED_KSYMS)

#include <generated/autoksyms.h>

/*
 * For fine grained build dependencies, we want to tell the build system
 * about each possible exported symbol even if they're not actually exported.
 * We use a symbol pattern __ksym_marker_<symbol> that the build system filters
 * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
 * discarded in the final link stage.
 */
#define __ksym_marker(sym)	\
	static int __ksym_marker_##sym[0] __section(".discard.ksym") __used

#define __EXPORT_SYMBOL(sym, sec)				\
	__ksym_marker(sym);					\
	__cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
#define __cond_export_sym(sym, sec, conf)			\
	___cond_export_sym(sym, sec, conf)
#define ___cond_export_sym(sym, sec, enabled)			\
	__cond_export_sym_##enabled(sym, sec)
#define __cond_export_sym_1(sym, sec) ___EXPORT_SYMBOL(sym, sec)
#define __cond_export_sym_0(sym, sec) /* nothing */

#define __EXPORT_SYMBOL_NS(sym, sec, ns)				\
	__ksym_marker(sym);						\
	__cond_export_ns_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
#define __cond_export_ns_sym(sym, sec, ns, conf)			\
	___cond_export_ns_sym(sym, sec, ns, conf)
#define ___cond_export_ns_sym(sym, sec, ns, enabled)			\
	__cond_export_ns_sym_##enabled(sym, sec, ns)
#define __cond_export_ns_sym_1(sym, sec, ns) ___EXPORT_SYMBOL_NS(sym, sec, ns)
#define __cond_export_ns_sym_0(sym, sec, ns) /* nothing */

#else

#define __EXPORT_SYMBOL_NS(sym,sec,ns)	___EXPORT_SYMBOL_NS(sym,sec,ns)
#define __EXPORT_SYMBOL(sym,sec)	___EXPORT_SYMBOL(sym,sec)

#endif /* CONFIG_MODULES */

#ifdef DEFAULT_SYMBOL_NAMESPACE
#undef __EXPORT_SYMBOL
#define __EXPORT_SYMBOL(sym, sec)				\
	__EXPORT_SYMBOL_NS(sym, sec, DEFAULT_SYMBOL_NAMESPACE)
#endif

#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")
#define EXPORT_SYMBOL_NS(sym, ns)	__EXPORT_SYMBOL_NS(sym, "", ns)
#define EXPORT_SYMBOL_NS_GPL(sym, ns)	__EXPORT_SYMBOL_NS(sym, "_gpl", ns)

#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 /* !__ASSEMBLY__ */

#endif /* _LINUX_EXPORT_H */