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