m4/ax_sys_weak_alias.m4

   1 # ===========================================================================
   2 # http://www.gnu.org/software/autoconf-archive/ax_sys_weak_alias.html
   3 # ===========================================================================
   4 #
   5 # SYNOPSIS
   6 #
   7 #   AX_SYS_WEAK_ALIAS
   8 #
   9 # DESCRIPTION
  10 #
  11 #   Determines whether weak aliases are supported on the system, and if so,
  12 #   what scheme is used to declare them. Also checks to see if aliases can
  13 #   cross object file boundaries, as some systems don't permit them to.
  14 #
  15 #   Most systems permit something called a "weak alias" or "weak symbol."
  16 #   These aliases permit a library to provide a stub form of a routine
  17 #   defined in another library, thus allowing the first library to operate
  18 #   even if the other library is not linked. This macro will check for
  19 #   support of weak aliases, figure out what schemes are available, and
  20 #   determine some characteristics of the weak alias support -- primarily,
  21 #   whether a weak alias declared in one object file may be referenced from
  22 #   another object file.
  23 #
  24 #   There are four known schemes of declaring weak symbols; each scheme is
  25 #   checked in turn, and the first one found is preferred. Note that only one
  26 #   of the mentioned preprocessor macros will be defined!
  27 #
  28 #   1. Function attributes
  29 #
  30 #   This scheme was first introduced by the GNU C compiler, and attaches
  31 #   attributes to particular functions. It is among the easiest to use, and
  32 #   so is the first one checked. If this scheme is detected, the
  33 #   preprocessor macro HAVE_SYS_WEAK_ALIAS_ATTRIBUTE will be defined to 1.
  34 #   This scheme is used as in the following code fragment:
  35 #
  36 #     void __weakf(int c)
  37 #     {
  38 #       /* Function definition... */
  39 #     }
  40 #
  41 #     void weakf(int c) __attribute__((weak, alias("__weakf")));
  42 #
  43 #   2. #pragma weak
  44 #
  45 #   This scheme is in use by many compilers other than the GNU C compiler.
  46 #   It is also particularly easy to use, and fairly portable -- well, as
  47 #   portable as these things get. If this scheme is detected first, the
  48 #   preprocessor macro HAVE_SYS_WEAK_ALIAS_PRAGMA will be defined to 1. This
  49 #   scheme is used as in the following code fragment:
  50 #
  51 #     extern void weakf(int c);
  52 #     #pragma weak weakf = __weakf
  53 #     void __weakf(int c)
  54 #     {
  55 #       /* Function definition... */
  56 #     }
  57 #
  58 #   3. #pragma _HP_SECONDARY_DEF
  59 #
  60 #   This scheme appears to be in use by the HP compiler. As it is rather
  61 #   specialized, this is one of the last schemes checked. If it is the first
  62 #   one detected, the preprocessor macro HAVE_SYS_WEAK_ALIAS_HPSECONDARY
  63 #   will be defined to 1. This scheme is used as in the following code
  64 #   fragment:
  65 #
  66 #     extern void weakf(int c);
  67 #     #pragma _HP_SECONDARY_DEF __weakf weakf
  68 #     void __weakf(int c)
  69 #     {
  70 #       /* Function definition... */
  71 #     }
  72 #
  73 #   4. #pragma _CRI duplicate
  74 #
  75 #   This scheme appears to be in use by the Cray compiler. As it is rather
  76 #   specialized, it too is one of the last schemes checked. If it is the
  77 #   first one detected, the preprocessor macro
  78 #   HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE will be defined to 1. This scheme is
  79 #   used as in the following code fragment:
  80 #
  81 #     extern void weakf(int c);
  82 #     #pragma _CRI duplicate weakf as __weakf
  83 #     void __weakf(int c)
  84 #     {
  85 #       /* Function definition... */
  86 #     }
  87 #
  88 #   In addition to the preprocessor macros listed above, if any scheme is
  89 #   found, the preprocessor macro HAVE_SYS_WEAK_ALIAS will also be defined
  90 #   to 1.
  91 #
  92 #   Once a weak aliasing scheme has been found, a check will be performed to
  93 #   see if weak aliases are honored across object file boundaries. If they
  94 #   are, the HAVE_SYS_WEAK_ALIAS_CROSSFILE preprocessor macro is defined to
  95 #   1.
  96 #
  97 #   This Autoconf macro also makes two substitutions. The first, WEAK_ALIAS,
  98 #   contains the name of the scheme found (one of "attribute", "pragma",
  99 #   "hpsecondary", or "criduplicate"), or "no" if no weak aliasing scheme
 100 #   was found. The second, WEAK_ALIAS_CROSSFILE, is set to "yes" or "no"
 101 #   depending on whether or not weak aliases may cross object file
 102 #   boundaries.
 103 #
 104 # LICENSE
 105 #
 106 #   Copyright (c) 2008 Kevin L. Mitchell <klmitch@mit.edu>
 107 #
 108 #   Copying and distribution of this file, with or without modification, are
 109 #   permitted in any medium without royalty provided the copyright notice
 110 #   and this notice are preserved. This file is offered as-is, without any
 111 #   warranty.
 112
 113 #serial 6
 114
 115 AU_ALIAS([KLM_SYS_WEAK_ALIAS], [AX_SYS_WEAK_ALIAS])
 116 AC_DEFUN([AX_SYS_WEAK_ALIAS], [
 117   # starting point: no aliasing scheme yet...
 118   ax_sys_weak_alias=no
 119
 120   # Figure out what kind of aliasing may be supported...
 121   _AX_SYS_WEAK_ALIAS_ATTRIBUTE
 122   _AX_SYS_WEAK_ALIAS_PRAGMA
 123   _AX_SYS_WEAK_ALIAS_HPSECONDARY
 124   _AX_SYS_WEAK_ALIAS_CRIDUPLICATE
 125
 126   # Do we actually support aliasing?
 127   AC_CACHE_CHECK([how to create weak aliases with $CC],
 128                  [ax_cv_sys_weak_alias],
 129  [ax_cv_sys_weak_alias=$ax_sys_weak_alias])
 130
 131   # OK, set a #define
 132   AS_IF([test $ax_cv_sys_weak_alias != no], [
 133     AC_DEFINE([HAVE_SYS_WEAK_ALIAS], 1,
 134               [Define this if your system can create weak aliases])
 135   ])
 136
 137   # Can aliases cross object file boundaries?
 138   _AX_SYS_WEAK_ALIAS_CROSSFILE
 139
 140   # OK, remember the results
 141   AC_SUBST([WEAK_ALIAS], [$ax_cv_sys_weak_alias])
 142   AC_SUBST([WEAK_ALIAS_CROSSFILE], [$ax_cv_sys_weak_alias_crossfile])
 143 ])
 144
 145 AC_DEFUN([_AX_SYS_WEAK_ALIAS_ATTRIBUTE],
 146 [ # Test whether compiler accepts __attribute__ form of weak aliasing
 147   AC_CACHE_CHECK([whether $CC accepts function __attribute__((weak,alias()))],
 148   [ax_cv_sys_weak_alias_attribute], [
 149     # We add -Werror if it's gcc to force an error exit if the weak attribute
 150     # isn't understood
 151     AS_IF([test $GCC = yes], [
 152       save_CFLAGS=$CFLAGS
 153       CFLAGS=-Werror])
 154
 155     # Try linking with a weak alias...
 156     AC_LINK_IFELSE([
 157       AC_LANG_PROGRAM([
 158 void __weakf(int c) {}
 159 void weakf(int c) __attribute__((weak, alias("__weakf")));],
 160         [weakf(0)])],
 161       [ax_cv_sys_weak_alias_attribute=yes],
 162       [ax_cv_sys_weak_alias_attribute=no])
 163
 164     # Restore original CFLAGS
 165     AS_IF([test $GCC = yes], [
 166       CFLAGS=$save_CFLAGS])
 167   ])
 168
 169   # What was the result of the test?
 170   AS_IF([test $ax_cv_sys_weak_alias_attribute = yes], [
 171     test $ax_sys_weak_alias = no && ax_sys_weak_alias=attribute
 172     AC_DEFINE([HAVE_SYS_WEAK_ALIAS_ATTRIBUTE], 1,
 173               [Define this if weak aliases may be created with __attribute__])
 174   ])
 175 ])
 176
 177 AC_DEFUN([_AX_SYS_WEAK_ALIAS_PRAGMA],
 178 [ # Test whether compiler accepts #pragma form of weak aliasing
 179   AC_CACHE_CHECK([whether $CC supports @%:@pragma weak],
 180   [ax_cv_sys_weak_alias_pragma], [
 181
 182     # Try linking with a weak alias...
 183     AC_LINK_IFELSE([
 184       AC_LANG_PROGRAM([
 185 extern void weakf(int c);
 186 @%:@pragma weak weakf = __weakf
 187 void __weakf(int c) {}],
 188         [weakf(0)])],
 189       [ax_cv_sys_weak_alias_pragma=yes],
 190       [ax_cv_sys_weak_alias_pragma=no])
 191   ])
 192
 193   # What was the result of the test?
 194   AS_IF([test $ax_cv_sys_weak_alias_pragma = yes], [
 195     test $ax_sys_weak_alias = no && ax_sys_weak_alias=pragma
 196     AC_DEFINE([HAVE_SYS_WEAK_ALIAS_PRAGMA], 1,
 197               [Define this if weak aliases may be created with @%:@pragma weak])
 198   ])
 199 ])
 200
 201 AC_DEFUN([_AX_SYS_WEAK_ALIAS_HPSECONDARY],
 202 [ # Test whether compiler accepts _HP_SECONDARY_DEF pragma from HP...
 203   AC_CACHE_CHECK([whether $CC supports @%:@pragma _HP_SECONDARY_DEF],
 204   [ax_cv_sys_weak_alias_hpsecondary], [
 205
 206     # Try linking with a weak alias...
 207     AC_LINK_IFELSE([
 208       AC_LANG_PROGRAM([
 209 extern void weakf(int c);
 210 @%:@pragma _HP_SECONDARY_DEF __weakf weakf
 211 void __weakf(int c) {}],
 212         [weakf(0)])],
 213       [ax_cv_sys_weak_alias_hpsecondary=yes],
 214       [ax_cv_sys_weak_alias_hpsecondary=no])
 215   ])
 216
 217   # What was the result of the test?
 218   AS_IF([test $ax_cv_sys_weak_alias_hpsecondary = yes], [
 219     test $ax_sys_weak_alias = no && ax_sys_weak_alias=hpsecondary
 220     AC_DEFINE([HAVE_SYS_WEAK_ALIAS_HPSECONDARY], 1,
 221               [Define this if weak aliases may be created with @%:@pragma _HP_SECONDARY_DEF])
 222   ])
 223 ])
 224
 225 AC_DEFUN([_AX_SYS_WEAK_ALIAS_CRIDUPLICATE],
 226 [ # Test whether compiler accepts "_CRI duplicate" pragma from Cray
 227   AC_CACHE_CHECK([whether $CC supports @%:@pragma _CRI duplicate],
 228   [ax_cv_sys_weak_alias_criduplicate], [
 229
 230     # Try linking with a weak alias...
 231     AC_LINK_IFELSE([
 232       AC_LANG_PROGRAM([
 233 extern void weakf(int c);
 234 @%:@pragma _CRI duplicate weakf as __weakf
 235 void __weakf(int c) {}],
 236         [weakf(0)])],
 237       [ax_cv_sys_weak_alias_criduplicate=yes],
 238       [ax_cv_sys_weak_alias_criduplicate=no])
 239   ])
 240
 241   # What was the result of the test?
 242   AS_IF([test $ax_cv_sys_weak_alias_criduplicate = yes], [
 243     test $ax_sys_weak_alias = no && ax_sys_weak_alias=criduplicate
 244     AC_DEFINE([HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE], 1,
 245               [Define this if weak aliases may be created with @%:@pragma _CRI duplicate])
 246   ])
 247 ])
 248
 249 dnl Note: This macro is modeled closely on AC_LINK_IFELSE, and in fact
 250 dnl depends on some implementation details of that macro, particularly
 251 dnl its use of _AC_MSG_LOG_CONFTEST to log the failed test program and
 252 dnl its use of ac_link for running the linker.
 253 AC_DEFUN([_AX_SYS_WEAK_ALIAS_CROSSFILE],
 254 [ # Check to see if weak aliases can cross object file boundaries
 255   AC_CACHE_CHECK([whether $CC supports weak aliases across object file boundaries],
 256   [ax_cv_sys_weak_alias_crossfile], [
 257     AS_IF([test $ax_cv_sys_weak_alias = no],
 258           [ax_cv_sys_weak_alias_crossfile=no], [
 259 dnl Must build our own test files...
 260       # conftest1 contains our weak alias definition...
 261       cat >conftest1.$ac_ext <<_ACEOF
 262 /* confdefs.h.  */
 263 _ACEOF
 264       cat confdefs.h >>conftest1.$ac_ext
 265       cat >>conftest1.$ac_ext <<_ACEOF
 266 /* end confdefs.h.  */
 267
 268 @%:@ifndef HAVE_SYS_WEAK_ALIAS_ATTRIBUTE
 269 extern void weakf(int c);
 270 @%:@if defined(HAVE_SYS_WEAK_ALIAS_PRAGMA)
 271 @%:@pragma weak weakf = __weakf
 272 @%:@elif defined(HAVE_SYS_WEAK_ALIAS_HPSECONDARY)
 273 @%:@pragma _HP_SECONDARY_DEF __weakf weakf
 274 @%:@elif defined(HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE)
 275 @%:@pragma _CRI duplicate weakf as __weakf
 276 @%:@endif
 277 @%:@endif
 278 void __weakf(int c) {}
 279 @%:@ifdef HAVE_SYS_WEAK_ALIAS_ATTRIBUTE
 280 void weakf(int c) __attribute((weak, alias("__weakf")));
 281 @%:@endif
 282 _ACEOF
 283       # And conftest2 contains our main routine that calls it
 284       cat >conftest2.$ac_ext <<_ACEOF
 285 /* confdefs.h.  */
 286 _ACEOF
 287       cat confdefs.h >> conftest2.$ac_ext
 288       cat >>conftest2.$ac_ext <<_ACEOF
 289 /* end confdefs.h.  */
 290
 291 extern void weakf(int c);
 292 int
 293 main ()
 294 {
 295   weakf(0);
 296   return 0;
 297 }
 298 _ACEOF
 299       # We must remove the object files (if any) ourselves...
 300       rm -f conftest2.$ac_objext conftest$ac_exeext
 301
 302       # Change ac_link to compile *2* files together
 303       save_aclink=$ac_link
 304       ac_link=`echo "$ac_link" | \
 305                sed -e 's/conftest\(\.\$ac_ext\)/conftest1\1 conftest2\1/'`
 306 dnl Substitute our own routine for logging the conftest
 307 m4_pushdef([_AC_MSG_LOG_CONFTEST],
 308 [echo "$as_me: failed program was:" >&AS_MESSAGE_LOG_FD
 309 echo ">>> conftest1.$ac_ext" >&AS_MESSAGE_LOG_FD
 310 sed "s/^/| /" conftest1.$ac_ext >&AS_MESSAGE_LOG_FD
 311 echo ">>> conftest2.$ac_ext" >&AS_MESSAGE_LOG_FD
 312 sed "s/^/| /" conftest2.$ac_ext >&AS_MESSAGE_LOG_FD
 313 ])dnl
 314       # Since we created the files ourselves, don't use SOURCE argument
 315       AC_LINK_IFELSE(, [ax_cv_sys_weak_alias_crossfile=yes],
 316                      [ax_cv_sys_weak_alias_crossfile=no])
 317 dnl Restore _AC_MSG_LOG_CONFTEST
 318 m4_popdef([_AC_MSG_LOG_CONFTEST])dnl
 319       # Restore ac_link
 320       ac_link=$save_aclink
 321
 322       # We must remove the object files (if any) and C files ourselves...
 323       rm -f conftest1.$ac_ext conftest2.$ac_ext \
 324             conftest1.$ac_objext conftest2.$ac_objext
 325     ])
 326   ])
 327
 328   # What were the results of the test?
 329   AS_IF([test $ax_cv_sys_weak_alias_crossfile = yes], [
 330     AC_DEFINE([HAVE_SYS_WEAK_ALIAS_CROSSFILE], 1,
 331               [Define this if weak aliases in other files are honored])
 332   ])
 333 ])