LXR linux/include/linux/export.h

   1/* SPDX-License-Identifier: GPL-2.0-only */
   2#ifndef _LINUX_EXPORT_H
   3#define _LINUX_EXPORT_H
   4
   5/*
   6 * Export symbols from the kernel to modules.  Forked from module.h
   7 * to reduce the amount of pointless cruft we feed to gcc when only
   8 * exporting a simple symbol or two.
   9 *
  10 * Try not to add #includes here.  It slows compilation and makes kernel
  11 * hackers place grumpy comments in header files.
  12 */
  13
  14#ifndef __ASSEMBLY__
  15#ifdef MODULE
  16extern struct module __this_module;
  17#define THIS_MODULE (&__this_module)
  18#else
  19#define THIS_MODULE ((struct module *)0)
  20#endif
  21
  22#ifdef CONFIG_MODVERSIONS
  23/* Mark the CRC weak since genksyms apparently decides not to
  24 * generate a checksums for some symbols */
  25#if defined(CONFIG_MODULE_REL_CRCS)
  26#define __CRC_SYMBOL(sym, sec)                                          \
  27        asm("   .section \"___kcrctab" sec "+" #sym "\", \"a\"  \n"     \
  28            "   .weak   __crc_" #sym "                          \n"     \
  29            "   .long   __crc_" #sym " - .                      \n"     \
  30            "   .previous                                       \n")
  31#else
  32#define __CRC_SYMBOL(sym, sec)                                          \
  33        asm("   .section \"___kcrctab" sec "+" #sym "\", \"a\"  \n"     \
  34            "   .weak   __crc_" #sym "                          \n"     \
  35            "   .long   __crc_" #sym "                          \n"     \
  36            "   .previous                                       \n")
  37#endif
  38#else
  39#define __CRC_SYMBOL(sym, sec)
  40#endif
  41
  42#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
  43#include <linux/compiler.h>
  44/*
  45 * Emit the ksymtab entry as a pair of relative references: this reduces
  46 * the size by half on 64-bit architectures, and eliminates the need for
  47 * absolute relocations that require runtime processing on relocatable
  48 * kernels.
  49 */
  50#define __KSYMTAB_ENTRY(sym, sec)                                       \
  51        __ADDRESSABLE(sym)                                              \
  52        asm("   .section \"___ksymtab" sec "+" #sym "\", \"a\"  \n"     \
  53            "   .balign 4                                       \n"     \
  54            "__ksymtab_" #sym ":                                \n"     \
  55            "   .long   " #sym "- .                             \n"     \
  56            "   .long   __kstrtab_" #sym "- .                   \n"     \
  57            "   .long   __kstrtabns_" #sym "- .                 \n"     \
  58            "   .previous                                       \n")
  59
  60struct kernel_symbol {
  61        int value_offset;
  62        int name_offset;
  63        int namespace_offset;
  64};
  65#else
  66#define __KSYMTAB_ENTRY(sym, sec)                                       \
  67        static const struct kernel_symbol __ksymtab_##sym               \
  68        __attribute__((section("___ksymtab" sec "+" #sym), used))       \
  69        __aligned(sizeof(void *))                                       \
  70        = { (unsigned long)&sym, __kstrtab_##sym, __kstrtabns_##sym }
  71
  72struct kernel_symbol {
  73        unsigned long value;
  74        const char *name;
  75        const char *namespace;
  76};
  77#endif
  78
  79#ifdef __GENKSYMS__
  80
  81#define ___EXPORT_SYMBOL(sym, sec, ns)  __GENKSYMS_EXPORT_SYMBOL(sym)
  82
  83#else
  84
  85/* For every exported symbol, place a struct in the __ksymtab section */
  86#define ___EXPORT_SYMBOL(sym, sec, ns)                                  \
  87        extern typeof(sym) sym;                                         \
  88        __CRC_SYMBOL(sym, sec);                                         \
  89        static const char __kstrtab_##sym[]                             \
  90        __attribute__((section("__ksymtab_strings"), used, aligned(1))) \
  91        = #sym;                                                         \
  92        static const char __kstrtabns_##sym[]                           \
  93        __attribute__((section("__ksymtab_strings"), used, aligned(1))) \
  94        = ns;                                                           \
  95        __KSYMTAB_ENTRY(sym, sec)
  96
  97#endif
  98
  99#if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)
 100
 101/*
 102 * Allow symbol exports to be disabled completely so that C code may
 103 * be reused in other execution contexts such as the UEFI stub or the
 104 * decompressor.
 105 */
 106#define __EXPORT_SYMBOL(sym, sec, ns)
 107
 108#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
 109
 110#include <generated/autoksyms.h>
 111
 112/*
 113 * For fine grained build dependencies, we want to tell the build system
 114 * about each possible exported symbol even if they're not actually exported.
 115 * We use a symbol pattern __ksym_marker_<symbol> that the build system filters
 116 * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
 117 * discarded in the final link stage.
 118 */
 119#define __ksym_marker(sym)      \
 120        static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
 121
 122#define __EXPORT_SYMBOL(sym, sec, ns)                                   \
 123        __ksym_marker(sym);                                             \
 124        __cond_export_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
 125#define __cond_export_sym(sym, sec, ns, conf)                           \
 126        ___cond_export_sym(sym, sec, ns, conf)
 127#define ___cond_export_sym(sym, sec, ns, enabled)                       \
 128        __cond_export_sym_##enabled(sym, sec, ns)
 129#define __cond_export_sym_1(sym, sec, ns) ___EXPORT_SYMBOL(sym, sec, ns)
 130#define __cond_export_sym_0(sym, sec, ns) /* nothing */
 131
 132#else
 133
 134#define __EXPORT_SYMBOL(sym, sec, ns)   ___EXPORT_SYMBOL(sym, sec, ns)
 135
 136#endif /* CONFIG_MODULES */
 137
 138#ifdef DEFAULT_SYMBOL_NAMESPACE
 139#include <linux/stringify.h>
 140#define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, __stringify(DEFAULT_SYMBOL_NAMESPACE))
 141#else
 142#define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, "")
 143#endif
 144
 145#define EXPORT_SYMBOL(sym)              _EXPORT_SYMBOL(sym, "")
 146#define EXPORT_SYMBOL_GPL(sym)          _EXPORT_SYMBOL(sym, "_gpl")
 147#define EXPORT_SYMBOL_GPL_FUTURE(sym)   _EXPORT_SYMBOL(sym, "_gpl_future")
 148#define EXPORT_SYMBOL_NS(sym, ns)       __EXPORT_SYMBOL(sym, "", #ns)
 149#define EXPORT_SYMBOL_NS_GPL(sym, ns)   __EXPORT_SYMBOL(sym, "_gpl", #ns)
 150
 151#ifdef CONFIG_UNUSED_SYMBOLS
 152#define EXPORT_UNUSED_SYMBOL(sym)       _EXPORT_SYMBOL(sym, "_unused")
 153#define EXPORT_UNUSED_SYMBOL_GPL(sym)   _EXPORT_SYMBOL(sym, "_unused_gpl")
 154#else
 155#define EXPORT_UNUSED_SYMBOL(sym)
 156#define EXPORT_UNUSED_SYMBOL_GPL(sym)
 157#endif
 158
 159#endif /* !__ASSEMBLY__ */
 160
 161#endif /* _LINUX_EXPORT_H */
 162