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
  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 /* Define ALIAS as a strong alias for ORIGINAL.  */
  83 #define strong_alias_asm(original, alias)       \
  84   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
  85 #ifdef ASSEMBLER
  86 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
  87 #else
  88 #define strong_alias(original, alias)   \
  89   asm (".set " __SYMBOL_PREFIX #alias "," __SYMBOL_PREFIX #original);
  90 #endif
  91
  92 /* Define ALIAS as a weak alias for ORIGINAL.
  93    If weak aliases are not available, this defines a strong alias.  */
  94 #ifdef HAVE_WEAK_SYMBOLS
  95 #ifdef ASSEMBLER
  96 #define weak_alias(original, alias)     \
  97   .weak C_SYMBOL_NAME (alias);  \
  98   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
  99 #else
 100 #define weak_alias(original, alias) \
 101   asm (".weak " __SYMBOL_PREFIX #alias "\n" \
 102        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 103 #endif
 104 #else
 105 #define weak_alias(original, alias) strong_alias(original, alias)
 106 #endif
 107
 108
 109
 110 /* When the file using this macro is linked in, the linker
 111    will emit a warning message MSG.  */
 112 #ifdef HAVE_GNU_LD
 113 #ifdef HAVE_ELF
 114 #define link_warning(msg)                       \
 115   static const char __evoke_link_warning__[]    \
 116     __attribute__ ((section (".gnu.warning"))) = msg;
 117 #else
 118 #define link_warning(msg)               \
 119   asm(".stabs \"" msg "\",30,0,0,0\n"   \
 120       ".stabs \"__evoke_link_warning__\",1,0,0,0\n"\
 121       ".stabs \"__evoke_link_warning__\",2,0,0,0\n");
 122 #endif
 123 #else
 124 /* We will never be heard; they will all die horribly.  */
 125 #define link_warning(msg)
 126 #endif
 127
 128 /* A canned warning for sysdeps/stub functions.  */
 129 #define stub_warning(name) \
 130   link_warning ("warning: " #name " is not implemented and will always fail")
 131
 132 /*
 133 \f
 134 */
 135
 136 #ifdef HAVE_GNU_LD
 137
 138 /* Symbol set support macros.  */
 139
 140 #ifdef HAVE_ELF
 141
 142 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 143 #define text_set_element(set, symbol)   _elf_set_element(set, symbol)
 144 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 145 #define data_set_element(set, symbol)   _elf_set_element(set, symbol)
 146 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 147 #define bss_set_element(set, symbol)    _elf_set_element(set, symbol)
 148
 149 /* These are all done the same way in ELF.
 150    There is a new section created for each set.  */
 151 #define _elf_set_element(set, symbol) \
 152   static const void *const __elf_set_##set##_element_##symbol##__ \
 153     __attribute__ ((section (#set))) = &(symbol)
 154
 155 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 156    be able to use the set's contents.  */
 157 #define symbol_set_define(set)  symbol_set_declare(set)
 158
 159 /* Declare SET for use in this module, if defined in another module.  */
 160 #define symbol_set_declare(set) \
 161   extern void *const __start_##set, *const __stop_##set;
 162
 163 /* Return a pointer (void *const *) to the first element of SET.  */
 164 #define symbol_set_first_element(set)   (&__start_##set)
 165
 166 /* Return true iff PTR (a void *const *) has been incremented
 167    past the last element in SET.  */
 168 #define symbol_set_end_p(set, ptr)      ((ptr) >= &__stop_##set)
 169
 170 #else   /* Not ELF: a.out.  */
 171
 172 #define text_set_element(set, symbol)   \
 173   asm(".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 174 #define data_set_element(set, symbol)   \
 175   asm(".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 176 #define bss_set_element(set, symbol)    ?error Must use initialized data.
 177 #define symbol_set_define(set)          void *const (set)[1];
 178 #define symbol_set_declare(set)         extern void *const (set)[1];
 179
 180 #define symbol_set_first_element(set)   &(set)[1]
 181 #define symbol_set_end_p(set, ptr)      (*(ptr) == 0)
 182
 183 #endif  /* ELF.  */
 184 #endif  /* Have GNU ld.  */
 185
 186 #endif /* libc-symbols.h */