include/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, 1997, 1998, 2000 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 not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #ifndef _LIBC_SYMBOLS_H
  22 #define _LIBC_SYMBOLS_H 1
  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 /* And we also need the data for the reentrant functions.  */
  52 #define _REENTRANT      1
  53
  54 #include <config.h>
  55
  56 /* The symbols in all the user (non-_) macros are C symbols.
  57    HAVE_GNU_LD without HAVE_ELF implies a.out.  */
  58
  59 #if defined HAVE_ASM_WEAK_DIRECTIVE || defined HAVE_ASM_WEAKEXT_DIRECTIVE
  60 # define HAVE_WEAK_SYMBOLS
  61 #endif
  62
  63 #ifndef __SYMBOL_PREFIX
  64 # ifdef NO_UNDERSCORES
  65 #  define __SYMBOL_PREFIX
  66 # else
  67 #  define __SYMBOL_PREFIX "_"
  68 # endif
  69 #endif
  70
  71 #ifndef C_SYMBOL_NAME
  72 # ifdef NO_UNDERSCORES
  73 #  define C_SYMBOL_NAME(name) name
  74 # else
  75 #  define C_SYMBOL_NAME(name) _##name
  76 # endif
  77 #endif
  78
  79 #ifndef __ASSEMBLER__
  80 /* GCC understands weak symbols and aliases; use its interface where
  81    possible, instead of embedded assembly language.  */
  82
  83 /* Define ALIASNAME as a strong alias for NAME.  */
  84 # define strong_alias(name, aliasname) \
  85   extern __typeof (name) aliasname __attribute__ ((alias (#name)));
  86
  87 /* This comes between the return type and function name in
  88    a function definition to make that definition weak.  */
  89 # define weak_function __attribute__ ((weak))
  90 # define weak_const_function __attribute__ ((weak, __const__))
  91
  92 # ifdef HAVE_WEAK_SYMBOLS
  93
  94 /* Define ALIASNAME as a weak alias for NAME.
  95    If weak aliases are not available, this defines a strong alias.  */
  96 #  define weak_alias(name, aliasname) \
  97   extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
  98
  99 /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */
 100 #  ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 101 #   define weak_extern(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);
 102 #  else
 103 #   define weak_extern(symbol)      asm (".weak " __SYMBOL_PREFIX #symbol);
 104 #  endif
 105
 106 # else
 107
 108 #  define weak_alias(name, aliasname) strong_alias(name, aliasname)
 109 #  define weak_extern(symbol) /* Nothing. */
 110
 111 # endif
 112
 113 #else /* __ASSEMBLER__ */
 114
 115 # ifdef HAVE_ASM_SET_DIRECTIVE
 116 #  define strong_alias(original, alias)         \
 117   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 118   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
 119 # else
 120 #  define strong_alias(original, alias)         \
 121   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 122   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 123 # endif
 124
 125 # ifdef HAVE_WEAK_SYMBOLS
 126 #  ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 127 #   define weak_alias(original, alias)  \
 128   .weakext C_SYMBOL_NAME (alias), C_SYMBOL_NAME (original)
 129 #   define weak_extern(symbol)  \
 130   .weakext C_SYMBOL_NAME (symbol)
 131
 132 #  else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 133
 134 #   define weak_alias(original, alias)  \
 135   .weak C_SYMBOL_NAME (alias);  \
 136   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 137
 138 #   define weak_extern(symbol)  \
 139   .weak C_SYMBOL_NAME (symbol)
 140
 141 #  endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 142
 143 # else /* ! HAVE_WEAK_SYMBOLS */
 144
 145 #  define weak_alias(original, alias) strong_alias(original, alias)
 146 #  define weak_extern(symbol) /* Nothing */
 147 # endif /* ! HAVE_WEAK_SYMBOLS */
 148
 149 #endif /* __ASSEMBLER__ */
 150
 151 /* On some platforms we can make internal function calls (i.e., calls of
 152    functions not exported) a bit faster by using a different calling
 153    convention.  */
 154 #ifndef internal_function
 155 # define internal_function      /* empty */
 156 #endif
 157
 158 /* Prepare for the case that `__builtin_expect' is not available.  */
 159 #ifndef HAVE_BUILTIN_EXPECT
 160 # define __builtin_expect(expr, val) (expr)
 161 #endif
 162
 163 /* When a reference to SYMBOL is encountered, the linker will emit a
 164    warning message MSG.  */
 165 #ifdef HAVE_GNU_LD
 166 # ifdef HAVE_ELF
 167
 168 /* We want the .gnu.warning.SYMBOL section to be unallocated.  */
 169 #  ifdef HAVE_ASM_PREVIOUS_DIRECTIVE
 170 #   define __make_section_unallocated(section_string)   \
 171   asm(".section " section_string "; .previous");
 172 #  elif defined HAVE_ASM_POPSECTION_DIRECTIVE
 173 #   define __make_section_unallocated(section_string)   \
 174   asm(".pushsection " section_string "; .popsection");
 175 #  else
 176 #   define __make_section_unallocated(section_string)
 177 #  endif
 178
 179 #  ifdef HAVE_SECTION_QUOTES
 180 #   define link_warning(symbol, msg) \
 181   __make_section_unallocated (".gnu.warning." #symbol) \
 182   static const char __evoke_link_warning_##symbol[]     \
 183     __attribute__ ((section (".gnu.warning." #symbol "\"\n\t#\""))) = msg;
 184 #  else
 185 #   define link_warning(symbol, msg) \
 186   __make_section_unallocated (".gnu.warning." #symbol) \
 187   static const char __evoke_link_warning_##symbol[]     \
 188     __attribute__ ((section (".gnu.warning." #symbol "\n\t#"))) = msg;
 189 #  endif
 190 # else
 191 #  define link_warning(symbol, msg)             \
 192   asm(".stabs \"" msg "\",30,0,0,0\n"   \
 193       ".stabs \"" __SYMBOL_PREFIX #symbol "\",1,0,0,0\n");
 194 # endif
 195 #else
 196 /* We will never be heard; they will all die horribly.  */
 197 # define link_warning(symbol, msg)
 198 #endif
 199
 200 /* A canned warning for sysdeps/stub functions.  */
 201 #define stub_warning(name) \
 202   link_warning (name, \
 203                 "warning: " #name " is not implemented and will always fail")
 204
 205 /*
 206 \f
 207 */
 208
 209 #ifdef HAVE_GNU_LD
 210
 211 /* Symbol set support macros.  */
 212
 213 # ifdef HAVE_ELF
 214
 215 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 216 #  define text_set_element(set, symbol) _elf_set_element(set, symbol)
 217 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 218 #  define data_set_element(set, symbol) _elf_set_element(set, symbol)
 219 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 220 #  define bss_set_element(set, symbol)  _elf_set_element(set, symbol)
 221
 222 /* These are all done the same way in ELF.
 223    There is a new section created for each set.  */
 224 #  ifdef SHARED
 225 /* When building a shared library, make the set section writable,
 226    because it will need to be relocated at run time anyway.  */
 227 #   define _elf_set_element(set, symbol) \
 228   static const void *__elf_set_##set##_element_##symbol##__ \
 229     __attribute__ ((unused, section (#set))) = &(symbol)
 230 #  else
 231 #   define _elf_set_element(set, symbol) \
 232   static const void *const __elf_set_##set##_element_##symbol##__ \
 233     __attribute__ ((unused, section (#set))) = &(symbol)
 234 #  endif
 235
 236 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 237    be able to use the set's contents.  */
 238 #  define symbol_set_define(set)        symbol_set_declare(set)
 239
 240 /* Declare SET for use in this module, if defined in another module.  */
 241 #  define symbol_set_declare(set) \
 242   extern void *const __start_##set __attribute__ ((__weak__));          \
 243   extern void *const __stop_##set __attribute__ ((__weak__));           \
 244   weak_extern (__start_##set) weak_extern (__stop_##set)
 245
 246 /* Return a pointer (void *const *) to the first element of SET.  */
 247 #  define symbol_set_first_element(set) (&__start_##set)
 248
 249 /* Return true iff PTR (a void *const *) has been incremented
 250    past the last element in SET.  */
 251 #  define symbol_set_end_p(set, ptr)    ((ptr) >= &__stop_##set)
 252
 253 # else  /* Not ELF: a.out.  */
 254
 255 #  define text_set_element(set, symbol) \
 256   asm(".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 257 #  define data_set_element(set, symbol) \
 258   asm(".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 259 #  define bss_set_element(set, symbol)  ?error Must use initialized data.
 260 #  define symbol_set_define(set)        void *const (set)[1];
 261 #  define symbol_set_declare(set)       extern void *const (set)[1];
 262
 263 #  define symbol_set_first_element(set) &(set)[1]
 264 #  define symbol_set_end_p(set, ptr)    (*(ptr) == 0)
 265
 266 # endif /* ELF.  */
 267 #endif  /* Have GNU ld.  */
 268
 269 #if DO_VERSIONING
 270 # ifdef __ASSEMBLER__
 271 #  define symbol_version(real, name, version) \
 272      .symver real, name##@##version
 273 #  define default_symbol_version(real, name, version) \
 274      .symver real, name##@##@##version
 275 # else
 276 #  define symbol_version(real, name, version) \
 277      __asm__ (".symver " #real "," #name "@" #version)
 278 #  define default_symbol_version(real, name, version) \
 279      __asm__ (".symver " #real "," #name "@@" #version)
 280 # endif
 281 #else
 282 # define symbol_version(real, name, version)
 283 # define default_symbol_version(real, name, version) \
 284   strong_alias(real, name)
 285 #endif
 286
 287 #endif /* libc-symbols.h */