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 /* The symbols in all the user (non-_) macros are C symbols.  Predefined
  51    should be HAVE_WEAK_SYMBOLS and/or HAVE_ELF and/or HAVE_GNU_LD.
  52    HAVE_WEAK_SYMBOLS is implied by the other two.  HAVE_GNU_LD without
  53    HAVE_ELF implies a.out.  */
  54
  55 #ifndef HAVE_WEAK_SYMBOLS
  56 #if defined (HAVE_ELF) || defined (HAVE_GNU_LD)
  57 #define HAVE_WEAK_SYMBOLS
  58 #endif
  59 #endif
  60
  61 #ifndef __SYMBOL_PREFIX
  62 #ifdef HAVE_ELF
  63 #define NO_UNDERSCORES
  64 #else
  65 #include <sysdep.h>             /* Should define NO_UNDERSCORES.  */
  66 #endif
  67 #ifdef NO_UNDERSCORES
  68 #define __SYMBOL_PREFIX
  69 #else
  70 #define __SYMBOL_PREFIX "_"
  71 #endif
  72 #endif
  73
  74 #ifndef C_SYMBOL_NAME
  75 #ifdef NO_UNDERSCORES
  76 #define C_SYMBOL_NAME(name) name
  77 #else
  78 #define C_SYMBOL_NAME(name) _##name
  79 #endif
  80 #endif
  81
  82
  83 /* Define ALIAS as a strong alias for ORIGINAL.  */
  84 #ifdef HAVE_ASM_SET_DIRECTIVE
  85 #define strong_alias_asm(original, alias)       \
  86   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
  87   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
  88 #ifdef ASSEMBLER
  89 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
  90 #else
  91 #define strong_alias(original, alias)   \
  92   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
  93        ".set " __SYMBOL_PREFIX #alias "," __SYMBOL_PREFIX #original);
  94 #endif
  95 #else
  96 #define strong_alias_asm(original, alias)       \
  97   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
  98   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
  99 #ifdef ASSEMBLER
 100 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 101 #else
 102 #define strong_alias(original, alias)   \
 103   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 104        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 105 #endif
 106 #endif
 107
 108 /* Helper macros used above.  */
 109 #define __string_1(x) __string_0(x)
 110 #define __string_0(x) #x
 111
 112
 113 #ifdef HAVE_WEAK_SYMBOLS
 114 #ifdef ASSEMBLER
 115
 116 /* Define ALIAS as a weak alias for ORIGINAL.
 117    If weak aliases are not available, this defines a strong alias.  */
 118 #define weak_alias(original, alias)     \
 119   .weak C_SYMBOL_NAME (alias);  \
 120   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 121
 122 /* Declare SYMBOL to be weak.  */
 123 #define weak_symbol(symbol)     .weak C_SYMBOL_NAME (symbol)
 124
 125 #else
 126 #define weak_symbol(symbol)     asm (".weak " __SYMBOL_PREFIX #symbol);
 127 #define weak_alias(original, alias) \
 128   asm (".weak " __SYMBOL_PREFIX #alias "\n" \
 129        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 130 #endif
 131 #else
 132 #define weak_alias(original, alias) strong_alias(original, alias)
 133 #define weak_symbol(symbol)     /* Do nothing.  */
 134 #endif
 135
 136
 137 #if (!defined (ASSEMBLER) && \
 138      (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7)))
 139 /* GCC 2.7 and later has special syntax for weak symbols and aliases.
 140    Using that is better when possible, because the compiler and assembler
 141    are better clued in to what we are doing.  */
 142 #undef  strong_alias
 143 #define strong_alias(name, aliasname) \
 144   extern __typeof (name) aliasname __attribute__ ((alias (#name)));
 145
 146 #ifdef HAVE_WEAK_SYMBOLS
 147 #undef  weak_symbol
 148 #define weak_symbol(name) \
 149   extern __typeof (name) name __attribute__ ((weak));
 150 #undef  weak_alias
 151 #define weak_alias(name, aliasname) \
 152   extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
 153 #endif  /* HAVE_WEAK_SYMBOLS.  */
 154 #endif  /* Not ASSEMBLER, and GCC 2.7 or later.  */
 155
 156
 157
 158 /* When a reference to SYMBOL is encountered, the linker will emit a
 159    warning message MSG.  */
 160 #ifdef HAVE_GNU_LD
 161 #ifdef HAVE_ELF
 162 #define link_warning(symbol, msg)                       \
 163   static const char __evoke_link_warning_##symbol[]     \
 164     __attribute__ ((section (".gnu.warning." #symbol))) = msg;
 165 #else
 166 #define link_warning(symbol, msg)               \
 167   asm(".stabs \"" msg "\",30,0,0,0\n"   \
 168       ".stabs \"" __SYMBOL_PREFIX #symbol "\",1,0,0,0\n");
 169 #endif
 170 #else
 171 /* We will never be heard; they will all die horribly.  */
 172 #define link_warning(symbol, msg)
 173 #endif
 174
 175 /* A canned warning for sysdeps/stub functions.  */
 176 #define stub_warning(name) \
 177   link_warning (name, \
 178                 "warning: " #name " is not implemented and will always fail")
 179
 180 /*
 181 \f
 182 */
 183
 184 #ifdef HAVE_GNU_LD
 185
 186 /* Symbol set support macros.  */
 187
 188 #ifdef HAVE_ELF
 189
 190 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 191 #define text_set_element(set, symbol)   _elf_set_element(set, symbol)
 192 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 193 #define data_set_element(set, symbol)   _elf_set_element(set, symbol)
 194 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 195 #define bss_set_element(set, symbol)    _elf_set_element(set, symbol)
 196
 197 /* These are all done the same way in ELF.
 198    There is a new section created for each set.  */
 199 #ifdef PIC
 200 /* When building a shared library, make the set section writable,
 201    because it will need to be relocated at run time anyway.  */
 202 #define _elf_set_element(set, symbol) \
 203   static const void *__elf_set_##set##_element_##symbol##__ \
 204     __attribute__ ((unused, section (#set))) = &(symbol)
 205 #else
 206 #define _elf_set_element(set, symbol) \
 207   static const void *const __elf_set_##set##_element_##symbol##__ \
 208     __attribute__ ((unused, section (#set))) = &(symbol)
 209 #endif
 210
 211 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 212    be able to use the set's contents.  */
 213 #define symbol_set_define(set)  symbol_set_declare(set)
 214
 215 /* Declare SET for use in this module, if defined in another module.  */
 216 #define symbol_set_declare(set) \
 217   extern void *const __start_##set __attribute__ ((__weak__));  \
 218   extern void *const __stop_##set __attribute__ ((__weak__));
 219
 220 /* Return a pointer (void *const *) to the first element of SET.  */
 221 #define symbol_set_first_element(set)   (&__start_##set)
 222
 223 /* Return true iff PTR (a void *const *) has been incremented
 224    past the last element in SET.  */
 225 #define symbol_set_end_p(set, ptr)      ((ptr) >= &__stop_##set)
 226
 227 #else   /* Not ELF: a.out.  */
 228
 229 #define text_set_element(set, symbol)   \
 230   asm(".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 231 #define data_set_element(set, symbol)   \
 232   asm(".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 233 #define bss_set_element(set, symbol)    ?error Must use initialized data.
 234 #define symbol_set_define(set)          void *const (set)[1];
 235 #define symbol_set_declare(set)         extern void *const (set)[1];
 236
 237 #define symbol_set_first_element(set)   &(set)[1]
 238 #define symbol_set_end_p(set, ptr)      (*(ptr) == 0)
 239
 240 #endif  /* ELF.  */
 241 #endif  /* Have GNU ld.  */
 242
 243 #endif /* libc-symbols.h */