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_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 \f
  57 */
  58
  59 #ifndef ASSEMBLER
  60
  61 /* Define the macros `_' and `N_' for conveniently marking translatable
  62    strings in the libc source code.  */
  63
  64 #define N_(msgid)       msgid
  65
  66 #include <libintl.h>
  67 extern const char _libc_intl_domainname[];
  68
  69 #ifdef dgettext
  70 /* This is defined as an optimizing macro, so use it.  */
  71 #define _(msgid)        dgettext (_libc_intl_domainname, (msgid))
  72 #else
  73 /* Be sure to use only the __ name when `dgettext' is a plain function
  74    instead of an optimizing macro.  */
  75 #define _(msgid)        __dgettext (_libc_intl_domainname, (msgid))
  76 #endif
  77
  78 #endif
  79
  80 /*
  81 \f
  82 */
  83 /* The symbols in all the user (non-_) macros are C symbols.
  84    HAVE_GNU_LD without HAVE_ELF implies a.out.  */
  85
  86 #if defined (HAVE_ASM_WEAK_DIRECTIVE) || defined (HAVE_ASM_WEAKEXT_DIRECTIVE)
  87 #define HAVE_WEAK_SYMBOLS
  88 #endif
  89
  90 #ifndef __SYMBOL_PREFIX
  91 #ifdef NO_UNDERSCORES
  92 #define __SYMBOL_PREFIX
  93 #else
  94 #define __SYMBOL_PREFIX "_"
  95 #endif
  96 #endif
  97
  98 #ifndef C_SYMBOL_NAME
  99 #ifdef NO_UNDERSCORES
 100 #define C_SYMBOL_NAME(name) name
 101 #else
 102 #define C_SYMBOL_NAME(name) _##name
 103 #endif
 104 #endif
 105
 106
 107 /* Define ALIAS as a strong alias for ORIGINAL.  */
 108 #ifdef HAVE_ASM_SET_DIRECTIVE
 109 #define strong_alias_asm(original, alias)       \
 110   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 111   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
 112 #ifdef ASSEMBLER
 113 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 114 #else
 115 #define strong_alias(original, alias)   \
 116   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 117        ".set " __SYMBOL_PREFIX #alias "," __SYMBOL_PREFIX #original);
 118 #endif
 119 #else
 120 #define strong_alias_asm(original, alias)       \
 121   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 122   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 123 #ifdef ASSEMBLER
 124 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 125 #else
 126 #define strong_alias(original, alias)   \
 127   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 128        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 129 #endif
 130 #endif
 131
 132 /* Helper macros used above.  */
 133 #define __string_1(x) __string_0(x)
 134 #define __string_0(x) #x
 135
 136
 137 #ifdef HAVE_WEAK_SYMBOLS
 138
 139 #ifdef ASSEMBLER
 140
 141 #ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 142
 143 /* Define ALIAS as a weak alias for ORIGINAL.
 144    If weak aliases are not available, this defines a strong alias.  */
 145 #define weak_alias(original, alias)     \
 146   .weakext C_SYMBOL_NAME (alias), C_SYMBOL_NAME (original)
 147
 148 /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */
 149 #define weak_extern(symbol)     \
 150   .weakext C_SYMBOL_NAME (symbol)
 151
 152 #else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 153
 154 /* Define ALIAS as a weak alias for ORIGINAL.
 155    If weak aliases are not available, this defines a strong alias.  */
 156 #define weak_alias(original, alias)     \
 157   .weak C_SYMBOL_NAME (alias);  \
 158   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 159
 160
 161 /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */
 162 #define weak_extern(symbol)     \
 163   .weak C_SYMBOL_NAME (symbol)
 164
 165 #endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 166
 167 #else /* ! ASSEMBLER */
 168
 169 #ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 170 #define weak_extern_asm(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);
 171 #define weak_alias_asm(original, alias) \
 172   asm (".weakext " __SYMBOL_PREFIX #alias ", " __SYMBOL_PREFIX #original);
 173 #else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 174 #define weak_extern_asm(symbol) asm (".weak " __SYMBOL_PREFIX #symbol);
 175 #define weak_alias_asm(original, alias) \
 176   asm (".weak " __SYMBOL_PREFIX #alias "\n" \
 177        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 178 #endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 179
 180 #define weak_alias(o, a) weak_alias_asm (o, a)
 181 #define weak_extern(symbol) weak_extern_asm (symbol)
 182
 183 #endif /* ! ASSEMBLER */
 184 #else
 185 #define weak_alias(original, alias) strong_alias(original, alias)
 186 #define weak_extern(symbol)     /* Do nothing; the ref will be strong.  */
 187 #endif
 188
 189
 190 #if (!defined (ASSEMBLER) && \
 191      (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7)))
 192 /* GCC 2.7 and later has special syntax for weak symbols and aliases.
 193    Using that is better when possible, because the compiler and assembler
 194    are better clued in to what we are doing.  */
 195 #undef  strong_alias
 196 #define strong_alias(name, aliasname) \
 197   extern __typeof (name) aliasname __attribute__ ((alias (#name)));
 198
 199 #ifdef HAVE_WEAK_SYMBOLS
 200 #undef  weak_alias
 201 #define weak_alias(name, aliasname) \
 202   extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
 203
 204 /* This comes between the return type and function name in
 205    a function definition to make that definition weak.  */
 206 #define weak_function __attribute__ ((weak))
 207 #define weak_const_function __attribute__ ((weak, __const__))
 208
 209 #endif  /* HAVE_WEAK_SYMBOLS.  */
 210 #endif  /* Not ASSEMBLER, and GCC 2.7 or later.  */
 211
 212
 213 #ifndef weak_function
 214 /* If we do not have the __attribute__ ((weak)) syntax, there is no way we
 215    can define functions as weak symbols.  The compiler will emit a `.globl'
 216    directive for the function symbol, and a `.weak' directive in addition
 217    will produce an error from the assembler.  */
 218 #define weak_function /* empty */
 219 #define weak_const_function /* empty */
 220 #endif
 221
 222
 223 /* When a reference to SYMBOL is encountered, the linker will emit a
 224    warning message MSG.  */
 225 #ifdef HAVE_GNU_LD
 226 #ifdef HAVE_ELF
 227 #define link_warning(symbol, msg)                       \
 228   static const char __evoke_link_warning_##symbol[]     \
 229     __attribute__ ((section (".gnu.warning." #symbol))) = msg;
 230 #else
 231 #define link_warning(symbol, msg)               \
 232   asm(".stabs \"" msg "\",30,0,0,0\n"   \
 233       ".stabs \"" __SYMBOL_PREFIX #symbol "\",1,0,0,0\n");
 234 #endif
 235 #else
 236 /* We will never be heard; they will all die horribly.  */
 237 #define link_warning(symbol, msg)
 238 #endif
 239
 240 /* A canned warning for sysdeps/stub functions.  */
 241 #define stub_warning(name) \
 242   link_warning (name, \
 243                 "warning: " #name " is not implemented and will always fail")
 244
 245 /*
 246 \f
 247 */
 248
 249 #ifdef HAVE_GNU_LD
 250
 251 /* Symbol set support macros.  */
 252
 253 #ifdef HAVE_ELF
 254
 255 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 256 #define text_set_element(set, symbol)   _elf_set_element(set, symbol)
 257 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 258 #define data_set_element(set, symbol)   _elf_set_element(set, symbol)
 259 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 260 #define bss_set_element(set, symbol)    _elf_set_element(set, symbol)
 261
 262 /* These are all done the same way in ELF.
 263    There is a new section created for each set.  */
 264 #ifdef PIC
 265 /* When building a shared library, make the set section writable,
 266    because it will need to be relocated at run time anyway.  */
 267 #define _elf_set_element(set, symbol) \
 268   static const void *__elf_set_##set##_element_##symbol##__ \
 269     __attribute__ ((unused, section (#set))) = &(symbol)
 270 #else
 271 #define _elf_set_element(set, symbol) \
 272   static const void *const __elf_set_##set##_element_##symbol##__ \
 273     __attribute__ ((unused, section (#set))) = &(symbol)
 274 #endif
 275
 276 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 277    be able to use the set's contents.  */
 278 #define symbol_set_define(set)  symbol_set_declare(set)
 279
 280 /* Declare SET for use in this module, if defined in another module.  */
 281 #define symbol_set_declare(set) \
 282   extern void *const __start_##set __attribute__ ((__weak__));          \
 283   extern void *const __stop_##set __attribute__ ((__weak__));           \
 284   weak_extern (__start_##set) weak_extern (__stop_##set)
 285
 286 /* Return a pointer (void *const *) to the first element of SET.  */
 287 #define symbol_set_first_element(set)   (&__start_##set)
 288
 289 /* Return true iff PTR (a void *const *) has been incremented
 290    past the last element in SET.  */
 291 #define symbol_set_end_p(set, ptr)      ((ptr) >= &__stop_##set)
 292
 293 #else   /* Not ELF: a.out.  */
 294
 295 #define text_set_element(set, symbol)   \
 296   asm(".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 297 #define data_set_element(set, symbol)   \
 298   asm(".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 299 #define bss_set_element(set, symbol)    ?error Must use initialized data.
 300 #define symbol_set_define(set)          void *const (set)[1];
 301 #define symbol_set_declare(set)         extern void *const (set)[1];
 302
 303 #define symbol_set_first_element(set)   &(set)[1]
 304 #define symbol_set_end_p(set, ptr)      (*(ptr) == 0)
 305
 306 #endif  /* ELF.  */
 307 #endif  /* Have GNU ld.  */
 308
 309 #endif /* libc-symbols.h */