[RFC libdrm 1/6] configure: Support symbol visibility when available

[Thierry Reding <thierry.reding@gmail.com>]

From: Thierry Reding <treding@nvidia.com>

Checks whether or not the compiler supports the -fvisibility option. If
so it sets the VISIBILITY_CFLAGS variable which can be added to the per
directory AM_CFLAGS where appropriate.

Libraries can use the HAVE_VISIBILITY preprocessor definition to check
for availability and use something like this:

	#if defined(HAVE_VISIBILITY)
	#  define drm_private __attribute__((visibility("hidden")))
	#  define drm_public __attribute__((visibility("default")))
	#else
	#  define drm_private
	#  define drm_public
	#endif

By default all symbols will be hidden via the VISIBILITY_CFLAGS. Only
symbols explicitly marked drm_public will be exported.

Signed-off-by: Thierry Reding <treding@nvidia.com>
---
 configure.ac | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/configure.ac b/configure.ac
index d2d19d66dc17..3f4164238494 100644
--- a/configure.ac
+++ b/configure.ac
@@ -365,6 +365,26 @@ AC_ARG_WITH([kernel-source],
 	    [kernel_source="$with_kernel_source"])
 AC_SUBST(kernel_source)
 
+dnl Add flags for gcc and g++
+if test "x$GCC" = xyes; then
+    # Enable -fvisibility=hidden if using a gcc that supports it
+    save_CFLAGS="$CFLAGS"
+    AC_MSG_CHECKING([whether $CC supports -fvisibility=hidden])
+    VISIBILITY_CFLAGS="-fvisibility=hidden"
+    CFLAGS="$CFLAGS $VISIBILITY_CFLAGS"
+    AC_LINK_IFELSE([AC_LANG_PROGRAM()], AC_MSG_RESULT([yes]),
+                   [VISIBILITY_CFLAGS=""; AC_MSG_RESULT([no])]);
+
+    # Restore CFLAGS; VISIBILITY_CFLAGS are added to it where needed.
+    CFLAGS=$save_CFLAGS
+
+    if test "x$VISIBILITY_CFLAGS" != x; then
+        AC_DEFINE(HAVE_VISIBILITY, 1, [Compiler has -fvisibility support])
+    fi
+
+    AC_SUBST([VISIBILITY_CFLAGS])
+fi
+
 AC_SUBST(WARN_CFLAGS)
 AC_CONFIG_FILES([
 	Makefile
-- 
1.8.4.2