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
  52 #include <config.h>
  53 /*
  54 \f
  55 */
  56
  57 #ifndef ASSEMBLER
  58
  59 /* Define the macros `_' and `N_' for conveniently marking translatable
  60    strings in the libc source code.  */
  61
  62 #define N_(msgid)       msgid
  63
  64 #include <libintl.h>
  65 extern const char _libc_intl_domainname[];
  66
  67 #ifdef dgettext
  68 /* This is defined as an optimizing macro, so use it.  */
  69 #define _(msgid)        dgettext (_libc_intl_domainname, (msgid))
  70 #else
  71 /* Be sure to use only the __ name when `dgettext' is a plain function
  72    instead of an optimizing macro.  */
  73 #define _(msgid)        __dgettext (_libc_intl_domainname, (msgid))
  74 #endif
  75
  76 #endif
  77
  78 /*
  79 \f
  80 */
  81 /* The symbols in all the user (non-_) macros are C symbols.
  82    HAVE_GNU_LD without HAVE_ELF implies a.out.  */
  83
  84 #if defined (HAVE_ASM_WEAK_DIRECTIVE) || defined (HAVE_ASM_WEAKEXT_DIRECTIVE)
  85 #define HAVE_WEAK_SYMBOLS
  86 #endif
  87
  88 #ifndef __SYMBOL_PREFIX
  89 #ifdef NO_UNDERSCORES
  90 #define __SYMBOL_PREFIX
  91 #else
  92 #define __SYMBOL_PREFIX "_"
  93 #endif
  94 #endif
  95
  96 #ifndef C_SYMBOL_NAME
  97 #ifdef NO_UNDERSCORES
  98 #define C_SYMBOL_NAME(name) name
  99 #else
 100 #define C_SYMBOL_NAME(name) _##name
 101 #endif
 102 #endif
 103
 104
 105 /* Define ALIAS as a strong alias for ORIGINAL.  */
 106 #ifdef HAVE_ASM_SET_DIRECTIVE
 107 #define strong_alias_asm(original, alias)       \
 108   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 109   .set C_SYMBOL_NAME (alias),C_SYMBOL_NAME (original)
 110 #ifdef ASSEMBLER
 111 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 112 #else
 113 #define strong_alias(original, alias)   \
 114   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 115        ".set " __SYMBOL_PREFIX #alias "," __SYMBOL_PREFIX #original);
 116 #endif
 117 #else
 118 #define strong_alias_asm(original, alias)       \
 119   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (alias);   \
 120   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 121 #ifdef ASSEMBLER
 122 #define strong_alias(original, alias)   strong_alias_asm (original, alias)
 123 #else
 124 #define strong_alias(original, alias)   \
 125   asm (__string_1 (ASM_GLOBAL_DIRECTIVE) " " __SYMBOL_PREFIX #alias "\n" \
 126        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 127 #endif
 128 #endif
 129
 130 /* Helper macros used above.  */
 131 #define __string_1(x) __string_0(x)
 132 #define __string_0(x) #x
 133
 134
 135 #ifdef HAVE_WEAK_SYMBOLS
 136
 137 #ifdef ASSEMBLER
 138
 139 #ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 140
 141 /* Define ALIAS as a weak alias for ORIGINAL.
 142    If weak aliases are not available, this defines a strong alias.  */
 143 #define weak_alias(original, alias)     \
 144   .weakext C_SYMBOL_NAME (alias), C_SYMBOL_NAME (original)
 145
 146 /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */
 147 #define weak_extern(symbol)     \
 148   .weakext C_SYMBOL_NAME (symbol)
 149
 150 #else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 151
 152 /* Define ALIAS as a weak alias for ORIGINAL.
 153    If weak aliases are not available, this defines a strong alias.  */
 154 #define weak_alias(original, alias)     \
 155   .weak C_SYMBOL_NAME (alias);  \
 156   C_SYMBOL_NAME (alias) = C_SYMBOL_NAME (original)
 157
 158
 159 /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */
 160 #define weak_extern(symbol)     \
 161   .weak C_SYMBOL_NAME (symbol)
 162
 163 #endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 164
 165 #else /* ! ASSEMBLER */
 166
 167 #ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
 168 #define weak_extern_asm(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);
 169 #define weak_alias_asm(original, alias) \
 170   asm (".weakext " __SYMBOL_PREFIX #alias ", " __SYMBOL_PREFIX #original);
 171 #else /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 172 #define weak_extern_asm(symbol) asm (".weak " __SYMBOL_PREFIX #symbol);
 173 #define weak_alias_asm(original, alias) \
 174   asm (".weak " __SYMBOL_PREFIX #alias "\n" \
 175        __SYMBOL_PREFIX #alias " = " __SYMBOL_PREFIX #original);
 176 #endif /* ! HAVE_ASM_WEAKEXT_DIRECTIVE */
 177
 178 #define weak_alias(o, a) weak_alias_asm (o, a)
 179 #define weak_extern(symbol) weak_extern_asm (symbol)
 180
 181 #endif /* ! ASSEMBLER */
 182 #else
 183 #define weak_alias(original, alias) strong_alias(original, alias)
 184 #define weak_extern(symbol)     /* Do nothing; the ref will be strong.  */
 185 #endif
 186
 187
 188 #if (!defined (ASSEMBLER) && \
 189      (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7)))
 190 /* GCC 2.7 and later has special syntax for weak symbols and aliases.
 191    Using that is better when possible, because the compiler and assembler
 192    are better clued in to what we are doing.  */
 193 #undef  strong_alias
 194 #define strong_alias(name, aliasname) \
 195   extern __typeof (name) aliasname __attribute__ ((alias (#name)));
 196
 197 #ifdef HAVE_WEAK_SYMBOLS
 198 #undef  weak_alias
 199 #define weak_alias(name, aliasname) \
 200   extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));
 201
 202 /* This comes between the return type and function name in
 203    a function definition to make that definition weak.  */
 204 #define weak_function __attribute__ ((weak))
 205 #define weak_const_function __attribute__ ((weak, __const__))
 206
 207 #endif  /* HAVE_WEAK_SYMBOLS.  */
 208 #endif  /* Not ASSEMBLER, and GCC 2.7 or later.  */
 209
 210
 211 #ifndef weak_function
 212 /* If we do not have the __attribute__ ((weak)) syntax, there is no way we
 213    can define functions as weak symbols.  The compiler will emit a `.globl'
 214    directive for the function symbol, and a `.weak' directive in addition
 215    will produce an error from the assembler.  */
 216 #define weak_function /* empty */
 217 #define weak_const_function /* empty */
 218 #endif
 219
 220
 221 /* When a reference to SYMBOL is encountered, the linker will emit a
 222    warning message MSG.  */
 223 #ifdef HAVE_GNU_LD
 224 #ifdef HAVE_ELF
 225 #define link_warning(symbol, msg)                       \
 226   static const char __evoke_link_warning_##symbol[]     \
 227     __attribute__ ((section (".gnu.warning." #symbol))) = msg;
 228 #else
 229 #define link_warning(symbol, msg)               \
 230   asm(".stabs \"" msg "\",30,0,0,0\n"   \
 231       ".stabs \"" __SYMBOL_PREFIX #symbol "\",1,0,0,0\n");
 232 #endif
 233 #else
 234 /* We will never be heard; they will all die horribly.  */
 235 #define link_warning(symbol, msg)
 236 #endif
 237
 238 /* A canned warning for sysdeps/stub functions.  */
 239 #define stub_warning(name) \
 240   link_warning (name, \
 241                 "warning: " #name " is not implemented and will always fail")
 242
 243 /*
 244 \f
 245 */
 246
 247 #ifdef HAVE_GNU_LD
 248
 249 /* Symbol set support macros.  */
 250
 251 #ifdef HAVE_ELF
 252
 253 /* Make SYMBOL, which is in the text segment, an element of SET.  */
 254 #define text_set_element(set, symbol)   _elf_set_element(set, symbol)
 255 /* Make SYMBOL, which is in the data segment, an element of SET.  */
 256 #define data_set_element(set, symbol)   _elf_set_element(set, symbol)
 257 /* Make SYMBOL, which is in the bss segment, an element of SET.  */
 258 #define bss_set_element(set, symbol)    _elf_set_element(set, symbol)
 259
 260 /* These are all done the same way in ELF.
 261    There is a new section created for each set.  */
 262 #ifdef PIC
 263 /* When building a shared library, make the set section writable,
 264    because it will need to be relocated at run time anyway.  */
 265 #define _elf_set_element(set, symbol) \
 266   static const void *__elf_set_##set##_element_##symbol##__ \
 267     __attribute__ ((unused, section (#set))) = &(symbol)
 268 #else
 269 #define _elf_set_element(set, symbol) \
 270   static const void *const __elf_set_##set##_element_##symbol##__ \
 271     __attribute__ ((unused, section (#set))) = &(symbol)
 272 #endif
 273
 274 /* Define SET as a symbol set.  This may be required (it is in a.out) to
 275    be able to use the set's contents.  */
 276 #define symbol_set_define(set)  symbol_set_declare(set)
 277
 278 /* Declare SET for use in this module, if defined in another module.  */
 279 #define symbol_set_declare(set) \
 280   extern void *const __start_##set __attribute__ ((__weak__));          \
 281   extern void *const __stop_##set __attribute__ ((__weak__));           \
 282   weak_extern (__start_##set) weak_extern (__stop_##set)
 283
 284 /* Return a pointer (void *const *) to the first element of SET.  */
 285 #define symbol_set_first_element(set)   (&__start_##set)
 286
 287 /* Return true iff PTR (a void *const *) has been incremented
 288    past the last element in SET.  */
 289 #define symbol_set_end_p(set, ptr)      ((ptr) >= &__stop_##set)
 290
 291 #else   /* Not ELF: a.out.  */
 292
 293 #define text_set_element(set, symbol)   \
 294   asm(".stabs \"" __SYMBOL_PREFIX #set "\",23,0,0," __SYMBOL_PREFIX #symbol)
 295 #define data_set_element(set, symbol)   \
 296   asm(".stabs \"" __SYMBOL_PREFIX #set "\",25,0,0," __SYMBOL_PREFIX #symbol)
 297 #define bss_set_element(set, symbol)    ?error Must use initialized data.
 298 #define symbol_set_define(set)          void *const (set)[1];
 299 #define symbol_set_declare(set)         extern void *const (set)[1];
 300
 301 #define symbol_set_first_element(set)   &(set)[1]
 302 #define symbol_set_end_p(set, ptr)      (*(ptr) == 0)
 303
 304 #endif  /* ELF.  */
 305 #endif  /* Have GNU ld.  */
 306
 307 #endif /* libc-symbols.h */