include/linux/export.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 #ifndef _LINUX_EXPORT_H
   3 #define _LINUX_EXPORT_H
   4
   5 #include <linux/stringify.h>
   6
   7 /*
   8  * Export symbols from the kernel to modules.  Forked from module.h
   9  * to reduce the amount of pointless cruft we feed to gcc when only
  10  * exporting a simple symbol or two.
  11  *
  12  * Try not to add #includes here.  It slows compilation and makes kernel
  13  * hackers place grumpy comments in header files.
  14  */
  15
  16 #ifndef __ASSEMBLY__
  17 #ifdef MODULE
  18 extern struct module __this_module;
  19 #define THIS_MODULE (&__this_module)
  20 #else
  21 #define THIS_MODULE ((struct module *)0)
  22 #endif
  23
  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 4                                       \n"     \
  56             "__ksymtab_" #sym ":                                \n"     \
  57             "   .long   " #sym "- .                             \n"     \
  58             "   .long   __kstrtab_" #sym "- .                   \n"     \
  59             "   .long   __kstrtabns_" #sym "- .                 \n"     \
  60             "   .previous                                       \n")
  61
  62 struct kernel_symbol {
  63         int value_offset;
  64         int name_offset;
  65         int namespace_offset;
  66 };
  67 #else
  68 #define __KSYMTAB_ENTRY(sym, sec)                                       \
  69         static const struct kernel_symbol __ksymtab_##sym               \
  70         __attribute__((section("___ksymtab" sec "+" #sym), used))       \
  71         __aligned(sizeof(void *))                                       \
  72         = { (unsigned long)&sym, __kstrtab_##sym, __kstrtabns_##sym }
  73
  74 struct kernel_symbol {
  75         unsigned long value;
  76         const char *name;
  77         const char *namespace;
  78 };
  79 #endif
  80
  81 #ifdef __GENKSYMS__
  82
  83 #define ___EXPORT_SYMBOL(sym, sec, ns)  __GENKSYMS_EXPORT_SYMBOL(sym)
  84
  85 #else
  86
  87 /*
  88  * For every exported symbol, do the following:
  89  *
  90  * - If applicable, place a CRC entry in the __kcrctab section.
  91  * - Put the name of the symbol and namespace (empty string "" for none) in
  92  *   __ksymtab_strings.
  93  * - Place a struct kernel_symbol entry in the __ksymtab section.
  94  *
  95  * note on .section use: we specify progbits since usage of the "M" (SHF_MERGE)
  96  * section flag requires it. Use '%progbits' instead of '@progbits' since the
  97  * former apparently works on all arches according to the binutils source.
  98  */
  99 #define ___EXPORT_SYMBOL(sym, sec, ns)                                          \
 100         extern typeof(sym) sym;                                                 \
 101         extern const char __kstrtab_##sym[];                                    \
 102         extern const char __kstrtabns_##sym[];                                  \
 103         __CRC_SYMBOL(sym, sec);                                                 \
 104         asm("   .section \"__ksymtab_strings\",\"aMS\",%progbits,1      \n"     \
 105             "__kstrtab_" #sym ":                                        \n"     \
 106             "   .asciz  \"" #sym "\"                                    \n"     \
 107             "__kstrtabns_" #sym ":                                      \n"     \
 108             "   .asciz  \"" ns "\"                                      \n"     \
 109             "   .previous                                               \n");   \
 110         __KSYMTAB_ENTRY(sym, sec)
 111
 112 #endif
 113
 114 #if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)
 115
 116 /*
 117  * Allow symbol exports to be disabled completely so that C code may
 118  * be reused in other execution contexts such as the UEFI stub or the
 119  * decompressor.
 120  */
 121 #define __EXPORT_SYMBOL(sym, sec, ns)
 122
 123 #elif defined(CONFIG_TRIM_UNUSED_KSYMS)
 124
 125 #include <generated/autoksyms.h>
 126
 127 /*
 128  * For fine grained build dependencies, we want to tell the build system
 129  * about each possible exported symbol even if they're not actually exported.
 130  * We use a symbol pattern __ksym_marker_<symbol> that the build system filters
 131  * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
 132  * discarded in the final link stage.
 133  */
 134 #define __ksym_marker(sym)      \
 135         static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
 136
 137 #define __EXPORT_SYMBOL(sym, sec, ns)                                   \
 138         __ksym_marker(sym);                                             \
 139         __cond_export_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
 140 #define __cond_export_sym(sym, sec, ns, conf)                           \
 141         ___cond_export_sym(sym, sec, ns, conf)
 142 #define ___cond_export_sym(sym, sec, ns, enabled)                       \
 143         __cond_export_sym_##enabled(sym, sec, ns)
 144 #define __cond_export_sym_1(sym, sec, ns) ___EXPORT_SYMBOL(sym, sec, ns)
 145
 146 #ifdef __GENKSYMS__
 147 #define __cond_export_sym_0(sym, sec, ns) __GENKSYMS_EXPORT_SYMBOL(sym)
 148 #else
 149 #define __cond_export_sym_0(sym, sec, ns) /* nothing */
 150 #endif
 151
 152 #else
 153
 154 #define __EXPORT_SYMBOL(sym, sec, ns)   ___EXPORT_SYMBOL(sym, sec, ns)
 155
 156 #endif /* CONFIG_MODULES */
 157
 158 #ifdef DEFAULT_SYMBOL_NAMESPACE
 159 #define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, __stringify(DEFAULT_SYMBOL_NAMESPACE))
 160 #else
 161 #define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, "")
 162 #endif
 163
 164 #define EXPORT_SYMBOL(sym)              _EXPORT_SYMBOL(sym, "")
 165 #define EXPORT_SYMBOL_GPL(sym)          _EXPORT_SYMBOL(sym, "_gpl")
 166 #define EXPORT_SYMBOL_NS(sym, ns)       __EXPORT_SYMBOL(sym, "", __stringify(ns))
 167 #define EXPORT_SYMBOL_NS_GPL(sym, ns)   __EXPORT_SYMBOL(sym, "_gpl", __stringify(ns))
 168
 169 #endif /* !__ASSEMBLY__ */
 170
 171 #endif /* _LINUX_EXPORT_H */