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 ASM_LINE_SEP
  80 # define ASM_LINE_SEP ;
  81 #endif
  82
  83 #ifndef __ASSEMBLER__
  84 /* GCC understands weak symbols and aliases; use its interface where
  85    possible, instead of embedded assembly language.  */
  86
  87 /* Define ALIASNAME as a strong alias for NAME.  */
  88 # define strong_alias(name, aliasname) _strong_alias(name, aliasname)
  89 # define _strong_alias(name, aliasname) \
  90   extern __typeof (name) aliasname __attribute__ ((alias (#name)));
  91
  92 /* This comes between the return type and function name in
  93    a function definition to make that definition weak.  */
  94 # define weak_function __attribute__ ((weak))
  95 # define weak_const_function __attribute__ ((weak, __const__))
  96
  97 # ifdef HAVE_WEAK_SYMBOLS
  98
  99 /* Define ALIASNAME as a weak alias for NAME.
 100    If weak aliases are not available, this defines a strong alias.  */
 101 #  define weak_alias(name, aliasname) _weak_alias (name, aliasname)
 102 #  define _weak_alias(name, aliasname) \
 103   extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
 104
 105 /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */
 106 #  define weak_extern(symbol) _weak_extern (symbol)
 107 #  ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 108 #   define _weak_extern(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);
 109 #  else
 110 #   define _weak_extern(symbol)    asm (".weak " __SYMBOL_PREFIX #symbol);
 111 #  endif
 112
 113 # else
 114
 115 #  define weak_alias(name, aliasname) strong_alias(name, aliasname)
 116 #  define weak_extern(symbol) /* Nothing. */
 117
 118 # endif
 119
 120 #else /* __ASSEMBLER__ */
 121
 122 # ifdef HAVE_ASM_SET_DIRECTIVE
 123 #  define strong_alias(original, alias)         \
 124   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias) ASM_LINE_SEP       \
 125   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
 126 # else
 127 #  ifdef HAVE_ASM_GLOBAL_DOT_NAME
 128 #   define strong_alias(original, alias)        \
 129   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias) ASM_LINE_SEP       \
 130   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original) ASM_LINE_SEP \
 131   ASM_GLOBAL_DIRECTIVE C_SYMBOL_DOT_NAME (alias) ASM_LINE_SEP   \
 132   C_SYMBOL_DOT_NAME (alias) = C_SYMBOL_DOT_NAME (original)
 133 #  else
 134 #   define strong_alias(original, alias)        \
 135   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias) ASM_LINE_SEP       \
 136   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 137 #  endif
 138 # endif
 139
 140 # ifdef HAVE_WEAK_SYMBOLS
 141 #  ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 142 #   define weak_alias(original, alias)  \
 143   .weakext C_SYMBOL_NAME (alias), C_SYMBOL_NAME (original)
 144 #   define weak_extern(symbol)  \
 145   .weakext C_SYMBOL_NAME (symbol)
 146
 147 #  else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 148
 149 #   ifdef HAVE_ASM_GLOBAL_DOT_NAME
 150 #    define weak_alias(original, alias) \
 151   .weak C_SYMBOL_NAME (alias) ASM_LINE_SEP                      \
 152   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original) ASM_LINE_SEP \
 153   .weak C_SYMBOL_DOT_NAME (alias) ASM_LINE_SEP                  \
 154   C_SYMBOL_DOT_NAME (alias) = C_SYMBOL_DOT_NAME (original)
 155 #   else
 156 #    define weak_alias(original, alias) \
 157   .weak C_SYMBOL_NAME (alias) ASM_LINE_SEP      \
 158   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 159 #   endif
 160
 161 #   define weak_extern(symbol)  \
 162   .weak C_SYMBOL_NAME (symbol)
 163
 164 #  endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 165
 166 # else /* ! HAVE_WEAK_SYMBOLS */
 167
 168 #  define weak_alias(original, alias) strong_alias(original, alias)
 169 #  define weak_extern(symbol) /* Nothing */
 170 # endif /* ! HAVE_WEAK_SYMBOLS */
 171
 172 #endif /* __ASSEMBLER__ */
 173
 174 /* On some platforms we can make internal function calls (i.e., calls of
 175    functions not exported) a bit faster by using a different calling
 176    convention.  */
 177 #ifndef internal_function
 178 # define internal_function      /* empty */
 179 #endif
 180
 181 /* Prepare for the case that `__builtin_expect' is not available.  */
 182 #ifndef HAVE_BUILTIN_EXPECT
 183 # define __builtin_expect(expr, val) (expr)
 184 #endif
 185
 186 /* Determine the return address.  */
 187 #define RETURN_ADDRESS(nr) \
 188   __builtin_extract_return_addr (__builtin_return_address (nr))
 189
 190 /* When a reference to SYMBOL is encountered, the linker will emit a
 191    warning message MSG.  */
 192 #ifdef HAVE_GNU_LD
 193 # ifdef HAVE_ELF
 194
 195 /* We want the .gnu.warning.SYMBOL section to be unallocated.  */
 196 #  ifdef HAVE_ASM_PREVIOUS_DIRECTIVE
 197 #   define __make_section_unallocated(section_string)   \
 198   asm (".section " section_string "\n\t.previous");
 199 #  elif defined HAVE_ASM_POPSECTION_DIRECTIVE
 200 #   define __make_section_unallocated(section_string)   \
 201   asm (".pushsection " section_string "\n\t.popsection");
 202 #  else
 203 #   define __make_section_unallocated(section_string)
 204 #  endif
 205
 206 /* Tacking on "\n\t#" to the section name makes gcc put it's bogus
 207    section attributes on what looks like a comment to the assembler.  */
 208 #  ifdef HAVE_SECTION_QUOTES
 209 #   define link_warning(symbol, msg) \
 210   __make_section_unallocated (".gnu.warning." #symbol) \
 211   static const char __evoke_link_warning_##symbol[]     \
 212     __attribute__ ((section (".gnu.warning." #symbol "\"\n\t#\""))) = msg;
 213 #  else
 214 #   define link_warning(symbol, msg) \
 215   __make_section_unallocated (".gnu.warning." #symbol) \
 216   static const char __evoke_link_warning_##symbol[]     \
 217     __attribute__ ((section (".gnu.warning." #symbol "\n\t#"))) = msg;
 218 #  endif
 219 # else
 220 #  define link_warning(symbol, msg)             \
 221   asm (".stabs \"" msg "\",30,0,0,0\n\t"        \
 222        ".stabs \"" __SYMBOL_PREFIX #symbol "\",1,0,0,0\n");
 223 # endif
 224 #else
 225 /* We will never be heard; they will all die horribly.  */
 226 # define link_warning(symbol, msg)
 227 #endif
 228
 229 /* A canned warning for sysdeps/stub functions.  */
 230 #define stub_warning(name) \
 231   link_warning (name, \
 232                 "warning: " #name " is not implemented and will always fail")
 233
 234 /*
 235 \f
 236 */
 237
 238 #ifdef HAVE_GNU_LD
 239
 240 /* Symbol set support macros.  */
 241
 242 # ifdef HAVE_ELF
 243
 244 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 245 #  define text_set_element(set, symbol) _elf_set_element(set, symbol)
 246 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 247 #  define data_set_element(set, symbol) _elf_set_element(set, symbol)
 248 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 249 #  define bss_set_element(set, symbol)  _elf_set_element(set, symbol)
 250
 251 /* These are all done the same way in ELF.
 252    There is a new section created for each set.  */
 253 #  ifdef SHARED
 254 /* When building a shared library, make the set section writable,
 255    because it will need to be relocated at run time anyway.  */
 256 #   define _elf_set_element(set, symbol) \
 257   static const void *__elf_set_##set##_element_##symbol##__ \
 258     __attribute__ ((unused, section (#set))) = &(symbol)
 259 #  else
 260 #   define _elf_set_element(set, symbol) \
 261   static const void *const __elf_set_##set##_element_##symbol##__ \
 262     __attribute__ ((unused, section (#set))) = &(symbol)
 263 #  endif
 264
 265 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 266    be able to use the set's contents.  */
 267 #  define symbol_set_define(set)        symbol_set_declare(set)
 268
 269 /* Declare SET for use in this module, if defined in another module.  */
 270 #  define symbol_set_declare(set) \
 271   extern void *const __start_##set __attribute__ ((__weak__));          \
 272   extern void *const __stop_##set __attribute__ ((__weak__));           \
 273   weak_extern (__start_##set) weak_extern (__stop_##set)
 274
 275 /* Return a pointer (void *const *) to the first element of SET.  */
 276 #  define symbol_set_first_element(set) (&__start_##set)
 277
 278 /* Return true iff PTR (a void *const *) has been incremented
 279    past the last element in SET.  */
 280 #  define symbol_set_end_p(set, ptr)    ((ptr) >= &__stop_##set)
 281
 282 # else  /* Not ELF: a.out.  */
 283
 284 #  define text_set_element(set, symbol) \
 285   asm (".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 286 #  define data_set_element(set, symbol) \
 287   asm (".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 288 #  define bss_set_element(set, symbol)  ?error Must use initialized data.
 289 #  define symbol_set_define(set)        void *const (set)[1];
 290 #  define symbol_set_declare(set)       extern void *const (set)[1];
 291
 292 #  define symbol_set_first_element(set) &(set)[1]
 293 #  define symbol_set_end_p(set, ptr)    (*(ptr) == 0)
 294
 295 # endif /* ELF.  */
 296 #endif  /* Have GNU ld.  */
 297
 298 #if DO_VERSIONING
 299 # define symbol_version(real, name, version) \
 300      _symbol_version(real, name, version)
 301 # define default_symbol_version(real, name, version) \
 302      _default_symbol_version(real, name, version)
 303 # ifdef __ASSEMBLER__
 304 #  define _symbol_version(real, name, version) \
 305      .symver real, name##@##version
 306 #  define _default_symbol_version(real, name, version) \
 307      .symver real, name##@##@##version
 308 # else
 309 #  define _symbol_version(real, name, version) \
 310      __asm__ (".symver " #real "," #name "@" #version)
 311 #  define _default_symbol_version(real, name, version) \
 312      __asm__ (".symver " #real "," #name "@@" #version)
 313 # endif
 314 #else
 315 # define symbol_version(real, name, version)
 316 # define default_symbol_version(real, name, version) \
 317   strong_alias(real, name)
 318 #endif
 319
 320 #endif /* libc-symbols.h */