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, 1996 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_ASM_SET_DIRECTIVE if we have `.set B, A' instead of `A = B'.
  31    * ASM_GLOBAL_DIRECTIVE with `.globl' or `.global'.
  32    * HAVE_GNU_LD if using GNU ld, with support for weak symbols in a.out,
  33    and for symbol set and warning messages extensions in a.out and ELF.
  34    * HAVE_ELF if using ELF, which supports weak symbols using `.weak'.
  35    * HAVE_ASM_WEAK_DIRECTIVE if we have weak symbols using `.weak'.
  36    * HAVE_ASM_WEAKEXT_DIRECTIVE if we have weak symbols using `.weakext'.
  37
  38    */
  39
  40 /* This is defined for the compilation of all C library code.  features.h
  41    tests this to avoid inclusion of stubs.h while compiling the library,
  42    before stubs.h has been generated.  Some library code that is shared
  43    with other packages also tests this symbol to see if it is being
  44    compiled as part of the C library.  We must define this before including
  45    config.h, because it makes some definitions conditional on whether libc
  46    itself is being compiled, or just some generator program.  */
  47 #define _LIBC   1
  48
  49 /* Enable declarations of GNU extensions, since we are compiling them.  */
  50 #define _GNU_SOURCE     1
  51
  52 #include <config.h>
  53
  54 /* This disables sccsid/rcsid strings in lots of code of non-GNU origin.  */
  55 #define lint    1
  56 /*
  57 \f
  58 */
  59
  60 #ifndef ASSEMBLER
  61
  62 /* Define the macros `_' and `N_' for conveniently marking translatable
  63    strings in the libc source code.  */
  64
  65 #define N_(msgid)       msgid
  66
  67 #include <libintl.h>
  68 extern const char _libc_intl_domainname[];
  69
  70 #ifdef dgettext
  71 /* This is defined as an optimizing macro, so use it.  */
  72 #define _(msgid)        dgettext (_libc_intl_domainname, (msgid))
  73 #else
  74 /* Be sure to use only the __ name when `dgettext' is a plain function
  75    instead of an optimizing macro.  */
  76 #define _(msgid)        __dgettext (_libc_intl_domainname, (msgid))
  77 #endif
  78
  79 #endif
  80
  81 /*
  82 \f
  83 */
  84 /* The symbols in all the user (non-_) macros are C symbols.
  85    HAVE_GNU_LD without HAVE_ELF implies a.out.  */
  86
  87 #if defined (HAVE_ASM_WEAK_DIRECTIVE) || defined (HAVE_ASM_WEAKEXT_DIRECTIVE)
  88 #define HAVE_WEAK_SYMBOLS
  89 #endif
  90
  91 #ifndef __SYMBOL_PREFIX
  92 #ifdef NO_UNDERSCORES
  93 #define __SYMBOL_PREFIX
  94 #else
  95 #define __SYMBOL_PREFIX "_"
  96 #endif
  97 #endif
  98
  99 #ifndef C_SYMBOL_NAME
 100 #ifdef NO_UNDERSCORES
 101 #define C_SYMBOL_NAME(name) name
 102 #else
 103 #define C_SYMBOL_NAME(name) _##name
 104 #endif
 105 #endif
 106
 107
 108 /* Define ALIAS as a strong alias for ORIGINAL.  */
 109 #ifdef HAVE_ASM_SET_DIRECTIVE
 110 #define strong_alias_asm(original, alias)       \
 111   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 112   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
 113 #ifdef ASSEMBLER
 114 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 115 #else
 116 #define strong_alias(original, alias)   \
 117   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 118        ".set " __SYMBOL_PREFIX #alias "," __SYMBOL_PREFIX #original);
 119 #endif
 120 #else
 121 #define strong_alias_asm(original, alias)       \
 122   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 123   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 124 #ifdef ASSEMBLER
 125 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 126 #else
 127 #define strong_alias(original, alias)   \
 128   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 129        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 130 #endif
 131 #endif
 132
 133 /* Helper macros used above.  */
 134 #define __string_1(x) __string_0(x)
 135 #define __string_0(x) #x
 136
 137
 138 #ifdef HAVE_WEAK_SYMBOLS
 139
 140 #ifdef ASSEMBLER
 141
 142 #ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 143
 144 /* Define ALIAS as a weak alias for ORIGINAL.
 145    If weak aliases are not available, this defines a strong alias.  */
 146 #define weak_alias(original, alias)     \
 147   .weakext C_SYMBOL_NAME (alias), C_SYMBOL_NAME (original)
 148
 149 /* Declare SYMBOL to be weak.  */
 150 #define weak_symbol(symbol)     .weakext C_SYMBOL_NAME (symbol)
 151
 152 #else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 153
 154 /* Define ALIAS as a weak alias for ORIGINAL.
 155    If weak aliases are not available, this defines a strong alias.  */
 156 #define weak_alias(original, alias)     \
 157   .weak C_SYMBOL_NAME (alias);  \
 158   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 159
 160 /* Declare SYMBOL to be weak.  */
 161 #define weak_symbol(symbol)     .weak C_SYMBOL_NAME (symbol)
 162
 163 #endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 164
 165 #else /* ! ASSEMBLER */
 166
 167 #ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 168 #define weak_symbol(symbol)     asm (".weakext " __SYMBOL_PREFIX #symbol);
 169 #define weak_alias(original, alias) \
 170   asm (".weakext " __SYMBOL_PREFIX #alias ", " __SYMBOL_PREFIX #original);
 171 #else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 172 #define weak_symbol(symbol)     asm (".weak " __SYMBOL_PREFIX #symbol);
 173 #define weak_alias(original, alias) \
 174   asm (".weak " __SYMBOL_PREFIX #alias "\n" \
 175        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 176 #endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 177 #endif /* ! ASSEMBLER */
 178 #else
 179 #define weak_alias(original, alias) strong_alias(original, alias)
 180 #define weak_symbol(symbol)     /* Do nothing.  */
 181 #endif
 182
 183
 184 #if (!defined (ASSEMBLER) && \
 185      (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8)))
 186 /* GCC 2.8 and later has special syntax for weak symbols and aliases.
 187    Using that is better when possible, because the compiler and assembler
 188    are better clued in to what we are doing.  */
 189 #undef  strong_alias
 190 #define strong_alias(name, aliasname) \
 191   __typeof (name) aliasname __attribute__ ((alias (#name)));
 192
 193 #ifdef HAVE_WEAK_SYMBOLS
 194 #undef  weak_symbol
 195 #define weak_symbol(name) \
 196   extern __typeof (name) name __attribute__ ((weak));
 197 #undef  weak_alias
 198 #define weak_alias(name, aliasname) \
 199   __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
 200 #endif  /* HAVE_WEAK_SYMBOLS.  */
 201 #endif  /* Not ASSEMBLER, and GCC 2.8 or later.  */
 202
 203
 204
 205 /* When a reference to SYMBOL is encountered, the linker will emit a
 206    warning message MSG.  */
 207 #ifdef HAVE_GNU_LD
 208 #ifdef HAVE_ELF
 209 #define link_warning(symbol, msg)                       \
 210   static const char __evoke_link_warning_##symbol[]     \
 211     __attribute__ ((section (".gnu.warning." #symbol))) = msg;
 212 #else
 213 #define link_warning(symbol, msg)               \
 214   asm(".stabs \"" msg "\",30,0,0,0\n"   \
 215       ".stabs \"" __SYMBOL_PREFIX #symbol "\",1,0,0,0\n");
 216 #endif
 217 #else
 218 /* We will never be heard; they will all die horribly.  */
 219 #define link_warning(symbol, msg)
 220 #endif
 221
 222 /* A canned warning for sysdeps/stub functions.  */
 223 #define stub_warning(name) \
 224   link_warning (name, \
 225                 "warning: " #name " is not implemented and will always fail")
 226
 227 /*
 228 \f
 229 */
 230
 231 #ifdef HAVE_GNU_LD
 232
 233 /* Symbol set support macros.  */
 234
 235 #ifdef HAVE_ELF
 236
 237 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 238 #define text_set_element(set, symbol)   _elf_set_element(set, symbol)
 239 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 240 #define data_set_element(set, symbol)   _elf_set_element(set, symbol)
 241 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 242 #define bss_set_element(set, symbol)    _elf_set_element(set, symbol)
 243
 244 /* These are all done the same way in ELF.
 245    There is a new section created for each set.  */
 246 #ifdef PIC
 247 /* When building a shared library, make the set section writable,
 248    because it will need to be relocated at run time anyway.  */
 249 #define _elf_set_element(set, symbol) \
 250   static const void *__elf_set_##set##_element_##symbol##__ \
 251     __attribute__ ((unused, section (#set))) = &(symbol)
 252 #else
 253 #define _elf_set_element(set, symbol) \
 254   static const void *const __elf_set_##set##_element_##symbol##__ \
 255     __attribute__ ((unused, section (#set))) = &(symbol)
 256 #endif
 257
 258 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 259    be able to use the set's contents.  */
 260 #define symbol_set_define(set)  symbol_set_declare(set)
 261
 262 /* Declare SET for use in this module, if defined in another module.  */
 263 #define symbol_set_declare(set) \
 264   extern void *const __start_##set __attribute__ ((__weak__));          \
 265   extern void *const __stop_##set __attribute__ ((__weak__));           \
 266   /* Gratuitously repeat weak decl, in case using broken GCC (<2.8).  */\
 267   weak_symbol (__start_##set) weak_symbol (__stop_##set)
 268
 269 /* Return a pointer (void *const *) to the first element of SET.  */
 270 #define symbol_set_first_element(set)   (&__start_##set)
 271
 272 /* Return true iff PTR (a void *const *) has been incremented
 273    past the last element in SET.  */
 274 #define symbol_set_end_p(set, ptr)      ((ptr) >= &__stop_##set)
 275
 276 #else   /* Not ELF: a.out.  */
 277
 278 #define text_set_element(set, symbol)   \
 279   asm(".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 280 #define data_set_element(set, symbol)   \
 281   asm(".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 282 #define bss_set_element(set, symbol)    ?error Must use initialized data.
 283 #define symbol_set_define(set)          void *const (set)[1];
 284 #define symbol_set_declare(set)         extern void *const (set)[1];
 285
 286 #define symbol_set_first_element(set)   &(set)[1]
 287 #define symbol_set_end_p(set, ptr)      (*(ptr) == 0)
 288
 289 #endif  /* ELF.  */
 290 #endif  /* Have GNU ld.  */
 291
 292 #endif /* libc-symbols.h */