Question about -fvisibility=hidden

[Coleen Phillimore]

We have a bug that claims on linux we can get a big performance 
improvement with this flag.   Is anyone in the openjdk community able to 
try this out and/or verify this claim?

Thanks,
Coleen

http://bugs.sun.com/view_bug.do?bug_id=6588413

"On compiling the JDK [JVM actually] code with the new gcc compiler 
option "-fvisibility=hidden"quite some speed improvements on all 
platforms are observed, but for it to work, SAP code which is marked 
with "JNI_EXPORT" needs to be exported correctly by the compiler. The 
attached patch fixes this.

The attached "jni_md.h.new" file is a version of the file, how it could 
look like.
% more jni_md.h.diff
--- jni_md.h    2007-07-19 15:13:07.661299000 +0200
+++ jni_md.h.new        2007-07-19 15:12:02.826109000 +0200
@@ -8,9 +8,16 @@
 #ifndef _JAVASOFT_JNI_MD_H_
 #define _JAVASOFT_JNI_MD_H_

-#define JNIEXPORT
-#define JNIIMPORT
-#define JNICALL
+#if defined(__GNUC__) && (__GNUC__ >= 4)
+# define JNIEXPORT     __attribute__((visibility("default")))
+# define JNIIMPORT     __attribute__((visibility("default")))
+# define JNICALL
+#else
+# define JNIEXPORT
+# define JNIIMPORT
+# define JNICALL
+#endif
+

 typedef int jint;
 #ifdef _LP64 /* 64-bit Solaris */