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