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dnl Check if the target supports weak.

AC_DEFUN([GCC_CHECK_ATTRIBUTE_WEAK], [

  AC_CACHE_CHECK([whether the target supports weak],

                 ac_cv_have_attribute_weak, [

  weakref_m4_saved_CFLAGS="$CFLAGS"

  CFLAGS="$CFLAGS -Werror"

  AC_TRY_COMPILE([void __attribute__((weak)) foo(void) { }],

                 [], ac_cv_have_attribute_weak=yes,

                 ac_cv_have_attribute_weak=no)

  CFLAGS="$weakref_m4_saved_CFLAGS"])

  if test x"$ac_cv_have_attribute_weak" = xyes; then

    AC_DEFINE(HAVE_ATTRIBUTE_WEAK, 1,

      [Define to 1 if the target supports __attribute__((weak)).])

  fi])

dnl Check whether weak refs work like the ELF ones.

dnl This means that the weak reference works without having to satify

dnl linkage for the item.

dnl There are targets (at least Darwin) where we have fully functional

dnl weakrefs at runtime, but must supply the referenced item at link time.

AC_DEFUN([GCC_CHECK_ELF_STYLE_WEAKREF], [

  AC_CACHE_CHECK([whether weak refs work like ELF],

                  ac_cv_have_elf_style_weakref, [

  weakref_m4_saved_CFLAGS="$CFLAGS"

  case "${host}" in

    *-apple-darwin*) CFLAGS="$CFLAGS -Wl,-undefined,dynamic_lookup" ;;

    *) ;;

  esac

  AC_RUN_IFELSE([AC_LANG_SOURCE([[

extern void fNotToBeFound(void) __attribute__((weak));

int main ()

{

  if (fNotToBeFound)

    return 1;

  else

    return 0;

}

]])], ac_cv_have_elf_style_weakref=yes, ac_cv_have_elf_style_weakref=no, [

case "${host}" in

  alpha*-dec-osf*) ac_cv_have_elf_style_weakref=no ;;

  *-apple-darwin[[89]]*) ac_cv_have_elf_style_weakref=no ;;

  *) ac_cv_have_elf_style_weakref=yes;;

esac])CFLAGS="$weakref_m4_saved_CFLAGS"])

if test x"$ac_cv_have_elf_style_weakref" = xyes; then

  AC_DEFINE(HAVE_ELF_STYLE_WEAKREF, 1, [Define to 1 if target has a weakref that works like the ELF one.])

fi])