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
  16 extern 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_NS(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
  60 #define __KSYMTAB_ENTRY(sym, sec)                                       \
  61         __ADDRESSABLE(sym)                                              \
  62         asm("   .section \"___ksymtab" sec "+" #sym "\", \"a\"  \n"     \
  63             "   .balign 4                                       \n"     \
  64             "__ksymtab_" #sym ":                                \n"     \
  65             "   .long   " #sym "- .                             \n"     \
  66             "   .long   __kstrtab_" #sym "- .                   \n"     \
  67             "   .long   0                                       \n"     \
  68             "   .previous                                       \n")
  69
  70 struct kernel_symbol {
  71         int value_offset;
  72         int name_offset;
  73         int namespace_offset;
  74 };
  75 #else
  76 #define __KSYMTAB_ENTRY_NS(sym, sec)                                    \
  77         static const struct kernel_symbol __ksymtab_##sym               \
  78         __attribute__((section("___ksymtab" sec "+" #sym), used))       \
  79         __aligned(sizeof(void *))                                       \
  80         = { (unsigned long)&sym, __kstrtab_##sym, __kstrtabns_##sym }
  81
  82 #define __KSYMTAB_ENTRY(sym, sec)                                       \
  83         static const struct kernel_symbol __ksymtab_##sym               \
  84         __attribute__((section("___ksymtab" sec "+" #sym), used))       \
  85         __aligned(sizeof(void *))                                       \
  86         = { (unsigned long)&sym, __kstrtab_##sym, NULL }
  87
  88 struct kernel_symbol {
  89         unsigned long value;
  90         const char *name;
  91         const char *namespace;
  92 };
  93 #endif
  94
  95 #ifdef __GENKSYMS__
  96
  97 #define ___EXPORT_SYMBOL(sym,sec)       __GENKSYMS_EXPORT_SYMBOL(sym)
  98 #define ___EXPORT_SYMBOL_NS(sym,sec,ns) __GENKSYMS_EXPORT_SYMBOL(sym)
  99
 100 #else
 101
 102 #define ___export_symbol_common(sym, sec)                               \
 103         extern typeof(sym) sym;                                         \
 104         __CRC_SYMBOL(sym, sec);                                         \
 105         static const char __kstrtab_##sym[]                             \
 106         __attribute__((section("__ksymtab_strings"), used, aligned(1))) \
 107         = #sym                                                          \
 108
 109 /* For every exported symbol, place a struct in the __ksymtab section */
 110 #define ___EXPORT_SYMBOL_NS(sym, sec, ns)                               \
 111         ___export_symbol_common(sym, sec);                              \
 112         static const char __kstrtabns_##sym[]                           \
 113         __attribute__((section("__ksymtab_strings"), used, aligned(1))) \
 114         = #ns;                                                          \
 115         __KSYMTAB_ENTRY_NS(sym, sec)
 116
 117 #define ___EXPORT_SYMBOL(sym, sec)                                      \
 118         ___export_symbol_common(sym, sec);                              \
 119         __KSYMTAB_ENTRY(sym, sec)
 120
 121 #endif
 122
 123 #if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)
 124
 125 /*
 126  * Allow symbol exports to be disabled completely so that C code may
 127  * be reused in other execution contexts such as the UEFI stub or the
 128  * decompressor.
 129  */
 130 #define __EXPORT_SYMBOL_NS(sym, sec, ns)
 131 #define __EXPORT_SYMBOL(sym, sec)
 132
 133 #elif defined(CONFIG_TRIM_UNUSED_KSYMS)
 134
 135 #include <generated/autoksyms.h>
 136
 137 /*
 138  * For fine grained build dependencies, we want to tell the build system
 139  * about each possible exported symbol even if they're not actually exported.
 140  * We use a symbol pattern __ksym_marker_<symbol> that the build system filters
 141  * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
 142  * discarded in the final link stage.
 143  */
 144 #define __ksym_marker(sym)      \
 145         static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
 146
 147 #define __EXPORT_SYMBOL(sym, sec)                               \
 148         __ksym_marker(sym);                                     \
 149         __cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
 150 #define __cond_export_sym(sym, sec, conf)                       \
 151         ___cond_export_sym(sym, sec, conf)
 152 #define ___cond_export_sym(sym, sec, enabled)                   \
 153         __cond_export_sym_##enabled(sym, sec)
 154 #define __cond_export_sym_1(sym, sec) ___EXPORT_SYMBOL(sym, sec)
 155 #define __cond_export_sym_0(sym, sec) /* nothing */
 156
 157 #define __EXPORT_SYMBOL_NS(sym, sec, ns)                                \
 158         __ksym_marker(sym);                                             \
 159         __cond_export_ns_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
 160 #define __cond_export_ns_sym(sym, sec, ns, conf)                        \
 161         ___cond_export_ns_sym(sym, sec, ns, conf)
 162 #define ___cond_export_ns_sym(sym, sec, ns, enabled)                    \
 163         __cond_export_ns_sym_##enabled(sym, sec, ns)
 164 #define __cond_export_ns_sym_1(sym, sec, ns) ___EXPORT_SYMBOL_NS(sym, sec, ns)
 165 #define __cond_export_ns_sym_0(sym, sec, ns) /* nothing */
 166
 167 #else
 168
 169 #define __EXPORT_SYMBOL_NS(sym,sec,ns)  ___EXPORT_SYMBOL_NS(sym,sec,ns)
 170 #define __EXPORT_SYMBOL(sym,sec)        ___EXPORT_SYMBOL(sym,sec)
 171
 172 #endif /* CONFIG_MODULES */
 173
 174 #ifdef DEFAULT_SYMBOL_NAMESPACE
 175 #undef __EXPORT_SYMBOL
 176 #define __EXPORT_SYMBOL(sym, sec)                               \
 177         __EXPORT_SYMBOL_NS(sym, sec, DEFAULT_SYMBOL_NAMESPACE)
 178 #endif
 179
 180 #define EXPORT_SYMBOL(sym)              __EXPORT_SYMBOL(sym, "")
 181 #define EXPORT_SYMBOL_GPL(sym)          __EXPORT_SYMBOL(sym, "_gpl")
 182 #define EXPORT_SYMBOL_GPL_FUTURE(sym)   __EXPORT_SYMBOL(sym, "_gpl_future")
 183 #define EXPORT_SYMBOL_NS(sym, ns)       __EXPORT_SYMBOL_NS(sym, "", ns)
 184 #define EXPORT_SYMBOL_NS_GPL(sym, ns)   __EXPORT_SYMBOL_NS(sym, "_gpl", ns)
 185
 186 #ifdef CONFIG_UNUSED_SYMBOLS
 187 #define EXPORT_UNUSED_SYMBOL(sym)       __EXPORT_SYMBOL(sym, "_unused")
 188 #define EXPORT_UNUSED_SYMBOL_GPL(sym)   __EXPORT_SYMBOL(sym, "_unused_gpl")
 189 #else
 190 #define EXPORT_UNUSED_SYMBOL(sym)
 191 #define EXPORT_UNUSED_SYMBOL_GPL(sym)
 192 #endif
 193
 194 #endif /* !__ASSEMBLY__ */
 195
 196 #endif /* _LINUX_EXPORT_H */