include/linux/export.h

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