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/*
  86 * For every exported symbol, do the following:
  87 *
  88 * - If applicable, place a CRC entry in the __kcrctab section.
  89 * - Put the name of the symbol and namespace (empty string "" for none) in
  90 *   __ksymtab_strings.
  91 * - Place a struct kernel_symbol entry in the __ksymtab section.
  92 *
  93 * note on .section use: we specify progbits since usage of the "M" (SHF_MERGE)
  94 * section flag requires it. Use '%progbits' instead of '@progbits' since the
  95 * former apparently works on all arches according to the binutils source.
  96 */
  97#define ___EXPORT_SYMBOL(sym, sec, ns)                                          \
  98        extern typeof(sym) sym;                                                 \
  99        extern const char __kstrtab_##sym[];                                    \
 100        extern const char __kstrtabns_##sym[];                                  \
 101        __CRC_SYMBOL(sym, sec);                                                 \
 102        asm("   .section \"__ksymtab_strings\",\"aMS\",%progbits,1      \n"     \
 103            "__kstrtab_" #sym ":                                        \n"     \
 104            "   .asciz  \"" #sym "\"                                    \n"     \
 105            "__kstrtabns_" #sym ":                                      \n"     \
 106            "   .asciz  \"" ns "\"                                      \n"     \
 107            "   .previous                                               \n");   \
 108        __KSYMTAB_ENTRY(sym, sec)
 109
 110#endif
 111
 112#if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)
 113
 114/*
 115 * Allow symbol exports to be disabled completely so that C code may
 116 * be reused in other execution contexts such as the UEFI stub or the
 117 * decompressor.
 118 */
 119#define __EXPORT_SYMBOL(sym, sec, ns)
 120
 121#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
 122
 123#include <generated/autoksyms.h>
 124
 125/*
 126 * For fine grained build dependencies, we want to tell the build system
 127 * about each possible exported symbol even if they're not actually exported.
 128 * We use a symbol pattern __ksym_marker_<symbol> that the build system filters
 129 * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
 130 * discarded in the final link stage.
 131 */
 132#define __ksym_marker(sym)      \
 133        static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
 134
 135#define __EXPORT_SYMBOL(sym, sec, ns)                                   \
 136        __ksym_marker(sym);                                             \
 137        __cond_export_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
 138#define __cond_export_sym(sym, sec, ns, conf)                           \
 139        ___cond_export_sym(sym, sec, ns, conf)
 140#define ___cond_export_sym(sym, sec, ns, enabled)                       \
 141        __cond_export_sym_##enabled(sym, sec, ns)
 142#define __cond_export_sym_1(sym, sec, ns) ___EXPORT_SYMBOL(sym, sec, ns)
 143
 144#ifdef __GENKSYMS__
 145#define __cond_export_sym_0(sym, sec, ns) __GENKSYMS_EXPORT_SYMBOL(sym)
 146#else
 147#define __cond_export_sym_0(sym, sec, ns) /* nothing */
 148#endif
 149
 150#else
 151
 152#define __EXPORT_SYMBOL(sym, sec, ns)   ___EXPORT_SYMBOL(sym, sec, ns)
 153
 154#endif /* CONFIG_MODULES */
 155
 156#ifdef DEFAULT_SYMBOL_NAMESPACE
 157#include <linux/stringify.h>
 158#define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, __stringify(DEFAULT_SYMBOL_NAMESPACE))
 159#else
 160#define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, "")
 161#endif
 162
 163#define EXPORT_SYMBOL(sym)              _EXPORT_SYMBOL(sym, "")
 164#define EXPORT_SYMBOL_GPL(sym)          _EXPORT_SYMBOL(sym, "_gpl")
 165#define EXPORT_SYMBOL_NS(sym, ns)       __EXPORT_SYMBOL(sym, "", #ns)
 166#define EXPORT_SYMBOL_NS_GPL(sym, ns)   __EXPORT_SYMBOL(sym, "_gpl", #ns)
 167
 168#endif /* !__ASSEMBLY__ */
 169
 170#endif /* _LINUX_EXPORT_H */
 171