Provide access to RTLD_NODELETE flag on Unix.

Introduce a new QLibrary::PreventUnloadHint to support the
RTLD_NODELETE flag support by dlcompat on Unix platforms.

Change-Id: Ib1327e968a2a888850ad1086a102a143f86c5090
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Giuseppe D'Angelo <dangelog@gmail.com>

src/corelib/plugin/qlibrary.cpp

@@ -163,6 +163,10 @@ static QBasicMutex qt_library_mutex;
     If this hint is given, the filename of the library consists of
     a path, which is a reference to an archive file, followed by
     a reference to the archive member.
+    \value PreventUnloadHint
+    Prevents the library from being unloaded from the address space if close()
+    is called. The library's static variables are not reinitialized if open()
+    is called at a later time.
 
     \sa loadHints
 */
@@ -1230,6 +1234,8 @@ QString QLibrary::errorString() const
     to the library \c shr_64.o in the archive file named \c libGL.a. This
     is only supported on the AIX platform.
 
+    Setting PreventUnloadHint will only apply on Unix platforms.
+
     The interpretation of the load hints is platform dependent, and if
     you use it you are probably making some assumptions on which platform
     you are compiling for, so use them only if you understand the consequences

src/corelib/plugin/qlibrary.h

@@ -68,7 +68,8 @@ public:
     enum LoadHint {
         ResolveAllSymbolsHint = 0x01,
         ExportExternalSymbolsHint = 0x02,
-        LoadArchiveMemberHint = 0x04
+        LoadArchiveMemberHint = 0x04,
+        PreventUnloadHint = 0x08
     };
     Q_DECLARE_FLAGS(LoadHints, LoadHint)
 

src/corelib/plugin/qlibrary_unix.cpp

@@ -167,6 +167,18 @@ bool QLibraryPrivate::load_sys()
         dlFlags |= RTLD_LOCAL;
     }
 #endif
+
+    // Provide access to RTLD_NODELETE flag on Unix
+    // From GNU documentation on RTLD_NODELETE:
+    // Do not unload the library during dlclose(). Consequently, the
+    // library's specific static variables are not reinitialized if the
+    // library is reloaded with dlopen() at a later time.
+#ifdef RTLD_NODELETE
+    if (loadHints & QLibrary::PreventUnloadHint) {
+        dlFlags |= RTLD_NODELETE;
+    }
+#endif
+
 #if defined(Q_OS_AIX)	// Not sure if any other platform actually support this thing.
     if (loadHints & QLibrary::LoadArchiveMemberHint) {
         dlFlags |= RTLD_MEMBER;