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