From d6f15183b4064af11ce78cbf8a55edb04ad4a672 Mon Sep 17 00:00:00 2001
From: Ivan Maidanski <ivmai@mail.ru>
Date: Thu, 15 Dec 2011 19:01:47 +0400
Subject: [PATCH] Instruct configure to hide internal libgc.so symbols if
 supported (GCC)

* configure.ac (ac_cv_fvisibility_hidden): New variable (set to "yes"
if only shared library is built and GCC supports "-fvisibility" option.
* configure.ac (CFLAGS): Add "-fvisibility=hidden" and
"-DGC_VISIBILITY_HIDDEN_SET" if ac_cv_fvisibility_hidden is "yes".
* include/gc_config_macros.h (GC_API): Force "default visibility"
attribute if GC_VISIBILITY_HIDDEN_SET (only if GCC and GC_BUILD).
* tests/staticrootstest.c (GC_VISIBILITY_HIDDEN_SET): Test the macro
and skip the test if defined (since "staticrootslib" symbols are of
hidden visibility).
---
 configure.ac               | 13 ++++++++++++-
 include/gc_config_macros.h |  3 ++-
 tests/staticrootstest.c    | 14 ++++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 0f96066..ab8b27c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -505,7 +505,18 @@ AC_MSG_RESULT($enable_shared)
 if test "${enable_shared}" == yes; then
   if test "${enable_static}" == no; then
     AC_DEFINE(GC_DLL)
-    # FIXME: Also pass -fvisibility=hidden option if GCC v4+ and not Win32.
+    if test "$GCC" = yes; then
+      # Pass -fvisibility=hidden option if supported
+      AC_MSG_CHECKING([whether gcc supports -fvisibility])
+      old_CFLAGS="$CFLAGS"
+      CFLAGS="-fvisibility=hidden $CFLAGS"
+      AC_TRY_COMPILE([],[], [ac_cv_fvisibility_hidden=yes],
+                     [ac_cv_fvisibility_hidden=no])
+      AS_IF([test "$ac_cv_fvisibility_hidden" = yes],
+            [CFLAGS="-DGC_VISIBILITY_HIDDEN_SET $CFLAGS"],
+            [CFLAGS="$old_CFLAGS"])
+      AC_MSG_RESULT($ac_cv_fvisibility_hidden)
+    fi
   fi
 fi
 
diff --git a/include/gc_config_macros.h b/include/gc_config_macros.h
index 73db584..d407a6b 100644
--- a/include/gc_config_macros.h
+++ b/include/gc_config_macros.h
@@ -195,7 +195,8 @@
 
 # elif defined(__GNUC__)
     /* Only matters if used in conjunction with -fvisibility=hidden option. */
-#   if __GNUC__ >= 4 && defined(GC_BUILD)
+#   if defined(GC_BUILD) && (__GNUC__ >= 4 \
+                             || defined(GC_VISIBILITY_HIDDEN_SET))
 #     define GC_API extern __attribute__((__visibility__("default")))
 #   endif
 # endif
diff --git a/tests/staticrootstest.c b/tests/staticrootstest.c
index 222f209..f0b45bb 100644
--- a/tests/staticrootstest.c
+++ b/tests/staticrootstest.c
@@ -9,6 +9,8 @@
 #include "gc.h"
 #include "gc_backptr.h"
 
+#ifndef GC_VISIBILITY_HIDDEN_SET
+
 struct treenode {
     struct treenode *x;
     struct treenode *y;
@@ -55,3 +57,15 @@ int main(void)
   }
   return 0;
 }
+
+#else
+
+/* Skip since symbols defined in staticrootslib are not visible */
+
+int main(void)
+{
+  printf("staticrootstest skipped\n");
+  return 0;
+}
+
+#endif
-- 
2.7.4