libc-symbols.h

   1 /* Support macros for making weak and strong aliases for symbols,
   2    and for using symbol sets and linker warnings with GNU ld.
   3 Copyright (C) 1995 Free Software Foundation, Inc.
   4 This file is part of the GNU C Library.
   5
   6 The GNU C Library is free software; you can redistribute it and/or
   7 modify it under the terms of the GNU Library General Public License as
   8 published by the Free Software Foundation; either version 2 of the
   9 License, or (at your option) any later version.
  10
  11 The GNU C Library is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 Library General Public License for more details.
  15
  16 You should have received a copy of the GNU Library General Public
  17 License along with the GNU C Library; see the file COPYING.LIB.  If
  18 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  19 Cambridge, MA 02139, USA.  */
  20
  21 #ifndef _LIBC_SYMBOLS_H
  22 #define _LIBC_SYMBOLS_H
  23
  24 /* This file's macros are included implicitly in the compilation of every
  25    file in the C library by -imacros.
  26
  27    We include config.h which is generated by configure.
  28    It should define for us the following symbols:
  29
  30    * HAVE_GNU_LD if using GNU ld, with support for weak symbols in a.out,
  31    and for symbol set and warning messages extensions in a.out and ELF.
  32    This implies HAVE_WEAK_SYMBOLS; set by --with-gnu-ld.
  33    * HAVE_ELF if using ELF, which supports weak symbols.
  34    This implies HAVE_WEAK_SYMBOLS; set by --with-elf.
  35
  36    * HAVE_WEAK_SYMBOLS if weak symbols are available in the assembler and
  37    linker being used.  Set by --with-weak-symbols.
  38
  39    */
  40 #include <config.h>
  41
  42 /* This is defined for the compilation of all C library code.
  43    features.h tests this to avoid inclusion of stubs.h while
  44    compiling the library, before stubs.h has been generated.
  45    Some library code that is shared with other packages also
  46    tests this symbol to see if it is being compiled as part
  47    of the C library.  */
  48 #define _LIBC   1
  49 /*
  50 \f
  51 */
  52
  53 #ifndef ASSEMBLER
  54 /*  Define the macro `_' for conveniently marking translatable strings
  55     in the libc source code.  */
  56 #include <libintl.h>
  57 extern const char _libc_intl_domainname[];
  58 #ifdef dgettext
  59 /* This is defined as an optimizing macro, so use it.  */
  60 #define _(msgid)        dgettext (_libc_intl_domainname, (msgid))
  61 #else
  62 /* Be sure to use only the __ name when `dgettext' is a plain function
  63    instead of an optimizing macro.  */
  64 #define _(msgid)        __dgettext (_libc_intl_domainname, (msgid))
  65 #endif
  66 #endif
  67
  68 /*
  69 \f
  70 */
  71 /* The symbols in all the user (non-_) macros are C symbols.  Predefined
  72    should be HAVE_WEAK_SYMBOLS and/or HAVE_ELF and/or HAVE_GNU_LD.
  73    HAVE_WEAK_SYMBOLS is implied by the other two.  HAVE_GNU_LD without
  74    HAVE_ELF implies a.out.  */
  75
  76 #ifndef HAVE_WEAK_SYMBOLS
  77 #if defined (HAVE_ELF) || defined (HAVE_GNU_LD)
  78 #define HAVE_WEAK_SYMBOLS
  79 #endif
  80 #endif
  81
  82 #ifndef __SYMBOL_PREFIX
  83 #ifdef HAVE_ELF
  84 #define NO_UNDERSCORES
  85 #else
  86 #include <sysdep.h>             /* Should define NO_UNDERSCORES.  */
  87 #endif
  88 #ifdef NO_UNDERSCORES
  89 #define __SYMBOL_PREFIX
  90 #else
  91 #define __SYMBOL_PREFIX "_"
  92 #endif
  93 #endif
  94
  95 #ifndef C_SYMBOL_NAME
  96 #ifdef NO_UNDERSCORES
  97 #define C_SYMBOL_NAME(name) name
  98 #else
  99 #define C_SYMBOL_NAME(name) _##name
 100 #endif
 101 #endif
 102
 103
 104 /* Define ALIAS as a strong alias for ORIGINAL.  */
 105 #ifdef HAVE_ASM_SET_DIRECTIVE
 106 #define strong_alias_asm(original, alias)       \
 107   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 108   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
 109 #ifdef ASSEMBLER
 110 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 111 #else
 112 #define strong_alias(original, alias)   \
 113   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 114        ".set " __SYMBOL_PREFIX #alias "," __SYMBOL_PREFIX #original);
 115 #endif
 116 #else
 117 #define strong_alias_asm(original, alias)       \
 118   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 119   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 120 #ifdef ASSEMBLER
 121 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 122 #else
 123 #define strong_alias(original, alias)   \
 124   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 125        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 126 #endif
 127 #endif
 128
 129 /* Helper macros used above.  */
 130 #define __string_1(x) __string_0(x)
 131 #define __string_0(x) #x
 132
 133
 134 #ifdef HAVE_WEAK_SYMBOLS
 135 #ifdef ASSEMBLER
 136
 137 /* Define ALIAS as a weak alias for ORIGINAL.
 138    If weak aliases are not available, this defines a strong alias.  */
 139 #define weak_alias(original, alias)     \
 140   .weak C_SYMBOL_NAME (alias);  \
 141   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 142
 143 /* Declare SYMBOL to be weak.  */
 144 #define weak_symbol(symbol)     .weak C_SYMBOL_NAME (symbol)
 145
 146 #else
 147 #define weak_symbol(symbol)     asm (".weak " __SYMBOL_PREFIX #symbol);
 148 #define weak_alias(original, alias) \
 149   asm (".weak " __SYMBOL_PREFIX #alias "\n" \
 150        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 151 #endif
 152 #else
 153 #define weak_alias(original, alias) strong_alias(original, alias)
 154 #define weak_symbol(symbol)     /* Do nothing.  */
 155 #endif
 156
 157
 158 #if (!defined (ASSEMBLER) && \
 159      (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8)))
 160 /* GCC 2.8 and later has special syntax for weak symbols and aliases.
 161    Using that is better when possible, because the compiler and assembler
 162    are better clued in to what we are doing.  */
 163 #undef  strong_alias
 164 #define strong_alias(name, aliasname) \
 165   extern __typeof (name) aliasname __attribute__ ((alias (#name)));
 166
 167 #ifdef HAVE_WEAK_SYMBOLS
 168 #undef  weak_symbol
 169 #define weak_symbol(name) \
 170   extern __typeof (name) name __attribute__ ((weak));
 171 #undef  weak_alias
 172 #define weak_alias(name, aliasname) \
 173   extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
 174 #endif  /* HAVE_WEAK_SYMBOLS.  */
 175 #endif  /* Not ASSEMBLER, and GCC 2.8 or later.  */
 176
 177
 178
 179 /* When a reference to SYMBOL is encountered, the linker will emit a
 180    warning message MSG.  */
 181 #ifdef HAVE_GNU_LD
 182 #ifdef HAVE_ELF
 183 #define link_warning(symbol, msg)                       \
 184   static const char __evoke_link_warning_##symbol[]     \
 185     __attribute__ ((section (".gnu.warning." #symbol))) = msg;
 186 #else
 187 #define link_warning(symbol, msg)               \
 188   asm(".stabs \"" msg "\",30,0,0,0\n"   \
 189       ".stabs \"" __SYMBOL_PREFIX #symbol "\",1,0,0,0\n");
 190 #endif
 191 #else
 192 /* We will never be heard; they will all die horribly.  */
 193 #define link_warning(symbol, msg)
 194 #endif
 195
 196 /* A canned warning for sysdeps/stub functions.  */
 197 #define stub_warning(name) \
 198   link_warning (name, \
 199                 "warning: " #name " is not implemented and will always fail")
 200
 201 /*
 202 \f
 203 */
 204
 205 #ifdef HAVE_GNU_LD
 206
 207 /* Symbol set support macros.  */
 208
 209 #ifdef HAVE_ELF
 210
 211 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 212 #define text_set_element(set, symbol)   _elf_set_element(set, symbol)
 213 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 214 #define data_set_element(set, symbol)   _elf_set_element(set, symbol)
 215 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 216 #define bss_set_element(set, symbol)    _elf_set_element(set, symbol)
 217
 218 /* These are all done the same way in ELF.
 219    There is a new section created for each set.  */
 220 #ifdef PIC
 221 /* When building a shared library, make the set section writable,
 222    because it will need to be relocated at run time anyway.  */
 223 #define _elf_set_element(set, symbol) \
 224   static const void *__elf_set_##set##_element_##symbol##__ \
 225     __attribute__ ((unused, section (#set))) = &(symbol)
 226 #else
 227 #define _elf_set_element(set, symbol) \
 228   static const void *const __elf_set_##set##_element_##symbol##__ \
 229     __attribute__ ((unused, section (#set))) = &(symbol)
 230 #endif
 231
 232 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 233    be able to use the set's contents.  */
 234 #define symbol_set_define(set)  symbol_set_declare(set)
 235
 236 /* Declare SET for use in this module, if defined in another module.  */
 237 #define symbol_set_declare(set) \
 238   extern void *const __start_##set __attribute__ ((__weak__));          \
 239   extern void *const __stop_##set __attribute__ ((__weak__));           \
 240   /* Gratuitously repeat weak decl, in case using broken GCC (<2.8).  */\
 241   weak_symbol (__start_##set) weak_symbol (__stop_##set)
 242
 243 /* Return a pointer (void *const *) to the first element of SET.  */
 244 #define symbol_set_first_element(set)   (&__start_##set)
 245
 246 /* Return true iff PTR (a void *const *) has been incremented
 247    past the last element in SET.  */
 248 #define symbol_set_end_p(set, ptr)      ((ptr) >= &__stop_##set)
 249
 250 #else   /* Not ELF: a.out.  */
 251
 252 #define text_set_element(set, symbol)   \
 253   asm(".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 254 #define data_set_element(set, symbol)   \
 255   asm(".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 256 #define bss_set_element(set, symbol)    ?error Must use initialized data.
 257 #define symbol_set_define(set)          void *const (set)[1];
 258 #define symbol_set_declare(set)         extern void *const (set)[1];
 259
 260 #define symbol_set_first_element(set)   &(set)[1]
 261 #define symbol_set_end_p(set, ptr)      (*(ptr) == 0)
 262
 263 #endif  /* ELF.  */
 264 #endif  /* Have GNU ld.  */
 265
 266 #endif /* libc-symbols.h */