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(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 struct 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
  72 struct 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 #define __cond_export_sym_0(sym, sec, ns) /* nothing */
 144
 145 #else
 146
 147 #define __EXPORT_SYMBOL(sym, sec, ns)   ___EXPORT_SYMBOL(sym, sec, ns)
 148
 149 #endif /* CONFIG_MODULES */
 150
 151 #ifdef DEFAULT_SYMBOL_NAMESPACE
 152 #include <linux/stringify.h>
 153 #define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, __stringify(DEFAULT_SYMBOL_NAMESPACE))
 154 #else
 155 #define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, "")
 156 #endif
 157
 158 #define EXPORT_SYMBOL(sym)              _EXPORT_SYMBOL(sym, "")
 159 #define EXPORT_SYMBOL_GPL(sym)          _EXPORT_SYMBOL(sym, "_gpl")
 160 #define EXPORT_SYMBOL_GPL_FUTURE(sym)   _EXPORT_SYMBOL(sym, "_gpl_future")
 161 #define EXPORT_SYMBOL_NS(sym, ns)       __EXPORT_SYMBOL(sym, "", #ns)
 162 #define EXPORT_SYMBOL_NS_GPL(sym, ns)   __EXPORT_SYMBOL(sym, "_gpl", #ns)
 163
 164 #ifdef CONFIG_UNUSED_SYMBOLS
 165 #define EXPORT_UNUSED_SYMBOL(sym)       _EXPORT_SYMBOL(sym, "_unused")
 166 #define EXPORT_UNUSED_SYMBOL_GPL(sym)   _EXPORT_SYMBOL(sym, "_unused_gpl")
 167 #else
 168 #define EXPORT_UNUSED_SYMBOL(sym)
 169 #define EXPORT_UNUSED_SYMBOL_GPL(sym)
 170 #endif
 171
 172 #endif /* !__ASSEMBLY__ */
 173
 174 #endif /* _LINUX_EXPORT_H */