# visibility.m4 serial 6

dnl Copyright (C) 2005, 2008, 2010-2020 Free Software Foundation, Inc.

dnl This file is free software; the Free Software Foundation

dnl gives unlimited permission to copy and/or distribute it,

dnl with or without modifications, as long as this notice is preserved.

dnl From Bruno Haible.

dnl Tests whether the compiler supports the command-line option

dnl -fvisibility=hidden and the function and variable attributes

dnl __attribute__((__visibility__("hidden"))) and

dnl __attribute__((__visibility__("default"))).

dnl Does *not* test for __visibility__("protected") - which has tricky

dnl semantics (see the 'vismain' test in glibc) and does not exist e.g. on

dnl Mac OS X.

dnl Does *not* test for __visibility__("internal") - which has processor

dnl dependent semantics.

dnl Does *not* test for #pragma GCC visibility push(hidden) - which is

dnl "really only recommended for legacy code".

dnl Set the variable CFLAG_VISIBILITY.

dnl Defines and sets the variable HAVE_VISIBILITY.

AC_DEFUN([gl_VISIBILITY],

[

  AC_REQUIRE([AC_PROG_CC])

  CFLAG_VISIBILITY=

  HAVE_VISIBILITY=0

  if test -n "$GCC"; then

    dnl First, check whether -Werror can be added to the command line, or

    dnl whether it leads to an error because of some other option that the

    dnl user has put into $CC $CFLAGS $CPPFLAGS.

    AC_CACHE_CHECK([whether the -Werror option is usable],

      [gl_cv_cc_vis_werror],

      [gl_save_CFLAGS="$CFLAGS"

       CFLAGS="$CFLAGS -Werror"

       AC_COMPILE_IFELSE(

         [AC_LANG_PROGRAM([[]], [[]])],

         [gl_cv_cc_vis_werror=yes],

         [gl_cv_cc_vis_werror=no])

       CFLAGS="$gl_save_CFLAGS"

      ])

    dnl Now check whether visibility declarations are supported.

    AC_CACHE_CHECK([for simple visibility declarations],

      [gl_cv_cc_visibility],

      [gl_save_CFLAGS="$CFLAGS"

       CFLAGS="$CFLAGS -fvisibility=hidden"

       dnl We use the option -Werror and a function dummyfunc, because on some

       dnl platforms (Cygwin 1.7) the use of -fvisibility triggers a warning

       dnl "visibility attribute not supported in this configuration; ignored"

       dnl at the first function definition in every compilation unit, and we

       dnl don't want to use the option in this case.

       if test $gl_cv_cc_vis_werror = yes; then

         CFLAGS="$CFLAGS -Werror"

       fi

       AC_COMPILE_IFELSE(

         [AC_LANG_PROGRAM(

            [[extern __attribute__((__visibility__("hidden"))) int hiddenvar;

              extern __attribute__((__visibility__("default"))) int exportedvar;

              extern __attribute__((__visibility__("hidden"))) int hiddenfunc (void);

              extern __attribute__((__visibility__("default"))) int exportedfunc (void);

              void dummyfunc (void) {}

            ]],

            [[]])],

         [gl_cv_cc_visibility=yes],

         [gl_cv_cc_visibility=no])

       CFLAGS="$gl_save_CFLAGS"

      ])

    if test $gl_cv_cc_visibility = yes; then

      CFLAG_VISIBILITY="-fvisibility=hidden"

      HAVE_VISIBILITY=1

    fi

  fi

  AC_SUBST([CFLAG_VISIBILITY])

  AC_SUBST([HAVE_VISIBILITY])

  AC_DEFINE_UNQUOTED([HAVE_VISIBILITY], [$HAVE_VISIBILITY],

    [Define to 1 or 0, depending whether the compiler supports simple visibility declarations.])

])