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 /*
  15  * This comment block is used by fixdep. Please do not remove.
  16  *
  17  * When CONFIG_MODVERSIONS is changed from n to y, all source files having
  18  * EXPORT_SYMBOL variants must be re-compiled because genksyms is run as a
  19  * side effect of the *.o build rule.
  20  */
  21
  22 #ifndef __ASSEMBLY__
  23 #ifdef MODULE
  24 extern struct module __this_module;
  25 #define THIS_MODULE (&__this_module)
  26 #else
  27 #define THIS_MODULE ((struct module *)0)
  28 #endif
  29
  30 #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
  31 #include <linux/compiler.h>
  32 /*
  33  * Emit the ksymtab entry as a pair of relative references: this reduces
  34  * the size by half on 64-bit architectures, and eliminates the need for
  35  * absolute relocations that require runtime processing on relocatable
  36  * kernels.
  37  */
  38 #define __KSYMTAB_ENTRY(sym, sec)                                       \
  39         __ADDRESSABLE(sym)                                              \
  40         asm("   .section \"___ksymtab" sec "+" #sym "\", \"a\"  \n"     \
  41             "   .balign 4                                       \n"     \
  42             "__ksymtab_" #sym ":                                \n"     \
  43             "   .long   " #sym "- .                             \n"     \
  44             "   .long   __kstrtab_" #sym "- .                   \n"     \
  45             "   .long   __kstrtabns_" #sym "- .                 \n"     \
  46             "   .previous                                       \n")
  47
  48 struct kernel_symbol {
  49         int value_offset;
  50         int name_offset;
  51         int namespace_offset;
  52 };
  53 #else
  54 #define __KSYMTAB_ENTRY(sym, sec)                                       \
  55         static const struct kernel_symbol __ksymtab_##sym               \
  56         __attribute__((section("___ksymtab" sec "+" #sym), used))       \
  57         __aligned(sizeof(void *))                                       \
  58         = { (unsigned long)&sym, __kstrtab_##sym, __kstrtabns_##sym }
  59
  60 struct kernel_symbol {
  61         unsigned long value;
  62         const char *name;
  63         const char *namespace;
  64 };
  65 #endif
  66
  67 #ifdef __GENKSYMS__
  68
  69 #define ___EXPORT_SYMBOL(sym, sec, ns)  __GENKSYMS_EXPORT_SYMBOL(sym)
  70
  71 #else
  72
  73 /*
  74  * For every exported symbol, do the following:
  75  *
  76  * - Put the name of the symbol and namespace (empty string "" for none) in
  77  *   __ksymtab_strings.
  78  * - Place a struct kernel_symbol entry in the __ksymtab section.
  79  *
  80  * note on .section use: we specify progbits since usage of the "M" (SHF_MERGE)
  81  * section flag requires it. Use '%progbits' instead of '@progbits' since the
  82  * former apparently works on all arches according to the binutils source.
  83  */
  84 #define ___EXPORT_SYMBOL(sym, sec, ns)                                          \
  85         extern typeof(sym) sym;                                                 \
  86         extern const char __kstrtab_##sym[];                                    \
  87         extern const char __kstrtabns_##sym[];                                  \
  88         asm("   .section \"__ksymtab_strings\",\"aMS\",%progbits,1      \n"     \
  89             "__kstrtab_" #sym ":                                        \n"     \
  90             "   .asciz  \"" #sym "\"                                    \n"     \
  91             "__kstrtabns_" #sym ":                                      \n"     \
  92             "   .asciz  \"" ns "\"                                      \n"     \
  93             "   .previous                                               \n");   \
  94         __KSYMTAB_ENTRY(sym, sec)
  95
  96 #endif
  97
  98 #if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)
  99
 100 /*
 101  * Allow symbol exports to be disabled completely so that C code may
 102  * be reused in other execution contexts such as the UEFI stub or the
 103  * decompressor.
 104  */
 105 #define __EXPORT_SYMBOL(sym, sec, ns)
 106
 107 #elif defined(CONFIG_TRIM_UNUSED_KSYMS)
 108
 109 #include <generated/autoksyms.h>
 110
 111 /*
 112  * For fine grained build dependencies, we want to tell the build system
 113  * about each possible exported symbol even if they're not actually exported.
 114  * We use a symbol pattern __ksym_marker_<symbol> that the build system filters
 115  * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
 116  * discarded in the final link stage.
 117  */
 118 #define __ksym_marker(sym)      \
 119         static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
 120
 121 #define __EXPORT_SYMBOL(sym, sec, ns)                                   \
 122         __ksym_marker(sym);                                             \
 123         __cond_export_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
 124 #define __cond_export_sym(sym, sec, ns, conf)                           \
 125         ___cond_export_sym(sym, sec, ns, conf)
 126 #define ___cond_export_sym(sym, sec, ns, enabled)                       \
 127         __cond_export_sym_##enabled(sym, sec, ns)
 128 #define __cond_export_sym_1(sym, sec, ns) ___EXPORT_SYMBOL(sym, sec, ns)
 129
 130 #ifdef __GENKSYMS__
 131 #define __cond_export_sym_0(sym, sec, ns) __GENKSYMS_EXPORT_SYMBOL(sym)
 132 #else
 133 #define __cond_export_sym_0(sym, sec, ns) /* nothing */
 134 #endif
 135
 136 #else
 137
 138 #define __EXPORT_SYMBOL(sym, sec, ns)   ___EXPORT_SYMBOL(sym, sec, ns)
 139
 140 #endif /* CONFIG_MODULES */
 141
 142 #ifdef DEFAULT_SYMBOL_NAMESPACE
 143 #include <linux/stringify.h>
 144 #define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, __stringify(DEFAULT_SYMBOL_NAMESPACE))
 145 #else
 146 #define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, "")
 147 #endif
 148
 149 #define EXPORT_SYMBOL(sym)              _EXPORT_SYMBOL(sym, "")
 150 #define EXPORT_SYMBOL_GPL(sym)          _EXPORT_SYMBOL(sym, "_gpl")
 151 #define EXPORT_SYMBOL_NS(sym, ns)       __EXPORT_SYMBOL(sym, "", #ns)
 152 #define EXPORT_SYMBOL_NS_GPL(sym, ns)   __EXPORT_SYMBOL(sym, "_gpl", #ns)
 153
 154 #endif /* !__ASSEMBLY__ */
 155
 156 #endif /* _LINUX_EXPORT_H */