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Fork the gl_visibility macro

That macro currently was broken. It added flags to $CFLAGS but then called the
C++ compiler. The result was that ZNC didn't compile with GCC 3, because it
tried to use -fvisibility=hidden which isn't supported in that GCC version.

A list of changes done to this macro is contained in a comment.

Signed-off-by: Uli Schlachter <psychon@znc.in>
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psychon committed Sep 22, 2011
1 parent 6f2335d commit 08cc624bccba1e8ba4d8e913363d459b0f2d8116
Showing with 88 additions and 1 deletion.
  1. +1 −1 configure.ac
  2. +87 −0 m4/znc_visibility.m4
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@@ -34,7 +34,7 @@ AC_PROG_GREP
AC_PROG_SED
AC_CANONICAL_HOST
AC_SYS_LARGEFILE
-gl_VISIBILITY
+ZNC_VISIBILITY
appendLib () {
if test "$LIBS" != ""; then
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@@ -0,0 +1,87 @@
+# visibility.m4 serial 3 (gettext-0.18)
+dnl Copyright (C) 2005, 2008-2010 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 Changes done by Uli Schlachter (C) 2011:
+dnl - Renamed everything from gl_ to znc_
+dnl - Instead of using CFLAGS, this now uses CXXFLAGS (the macro would actually
+dnl silently break if you called AC_LANG with anything but C before it)
+dnl - Because of the above, this now requiers AC_PROG_CXX and $GXX instead
+dnl of $GCC
+dnl - Added calls to AC_LANG_PUSH([C++]) and AC_LANG_POP
+dnl - Replaced AC_TRY_COMPILE with AC_COMPILE_IFELSE
+dnl - Added a definition for dummyfunc() so that this works with
+dnl -Wmissing-declarations
+
+dnl Tests whether the compiler supports the command-line option
+dnl -fvisibility=hidden and the function and variable attributes
+dnl __attribute__((__visibility__("hidden"))) and
+dnl __attribute__((__visibility__("default"))).
+dnl Does *not* test for __visibility__("protected") - which has tricky
+dnl semantics (see the 'vismain' test in glibc) and does not exist e.g. on
+dnl MacOS X.
+dnl Does *not* test for __visibility__("internal") - which has processor
+dnl dependent semantics.
+dnl Does *not* test for #pragma GCC visibility push(hidden) - which is
+dnl "really only recommended for legacy code".
+dnl Set the variable CFLAG_VISIBILITY.
+dnl Defines and sets the variable HAVE_VISIBILITY.
+
+AC_DEFUN([ZNC_VISIBILITY],
+[
+ AC_REQUIRE([AC_PROG_CXX])
+ AC_LANG_PUSH([C++])
+ CFLAG_VISIBILITY=
+ HAVE_VISIBILITY=0
+ if test -n "$GXX"; 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 $CPPFLAGS.
+ AC_MSG_CHECKING([whether the -Werror option is usable])
+ AC_CACHE_VAL([znc_cv_cc_vis_werror], [
+ znc_save_CXXFLAGS="$CXXFLAGS"
+ CXXFLAGS="$CXXFLAGS -Werror"
+ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [])],
+ [znc_cv_cc_vis_werror=yes],
+ [znc_cv_cc_vis_werror=no])
+ CXXFLAGS="$znc_save_CXXFLAGS"])
+ AC_MSG_RESULT([$znc_cv_cc_vis_werror])
+ dnl Now check whether visibility declarations are supported.
+ AC_MSG_CHECKING([for simple visibility declarations])
+ AC_CACHE_VAL([znc_cv_cc_visibility], [
+ znc_save_CXXFLAGS="$CXXFLAGS"
+ CXXFLAGS="$CXXFLAGS -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 $znc_cv_cc_vis_werror = yes; then
+ CXXFLAGS="$CXXFLAGS -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) {}]],
+ [])],
+ [znc_cv_cc_visibility=yes],
+ [znc_cv_cc_visibility=no])
+ CXXFLAGS="$znc_save_CXXFLAGS"])
+ AC_MSG_RESULT([$znc_cv_cc_visibility])
+ if test $znc_cv_cc_visibility = yes; then
+ CFLAG_VISIBILITY="-fvisibility=hidden"
+ HAVE_VISIBILITY=1
+ fi
+ fi
+ AC_SUBST([CFLAG_VISIBILITY])
+ AC_SUBST([HAVE_VISIBILITY])
+ AC_DEFINE_UNQUOTED([HAVE_VISIBILITY], [$HAVE_VISIBILITY],
+ [Define to 1 or 0, depending whether the compiler supports simple visibility declarations.])
+ AC_LANG_POP
+])

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