diff --git a/configure.ac b/configure.ac
index d576083..5ae5eca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -91,48 +91,36 @@ PKG_CHECK_MODULES([GTKMM],
 dnl use DSO visibility tags for systems that supports it correctly
 dnl (for example, GCC 4.0 and above)
 dnl see http://gcc.gnu.org/wiki/Visibility for more informations
-AC_MSG_CHECKING([whether the compiler supports DSO visibility attributes])
+AH_TEMPLATE([DLLEXPORT],[Attribute for objects to be exported from DSOs])
+AH_TEMPLATE([DLLIMPORT],[Attribute for objects to be imported from DSOs])
+AH_TEMPLATE([DLLLOCAL], [Attribute for objects local to current DSO])
+AH_TEMPLATE([DLLPUBLIC],[Attribute for DSO public objects])
+
+dnl for now it works only with GCC >= 4.0.0
+AC_MSG_CHECKING([whether GCC supports DSO visibility attributes])
 AC_LANG_PUSH([C++])
 AC_COMPILE_IFELSE(
 	AC_LANG_PROGRAM([], [
-		#if defined (GCC_HASCLASSVISIBILITY) || defined (WIN32) 
+		#if defined __GNUC__ && (__GNUC__) >= 4
 		return 0;
 		#else
 		bails out with a compilation error.
 		#endif
 	]),[
 		AC_MSG_RESULT([yes])
-		AH_VERBATIM([DLLEXPORT],[
-// DSO visibility support enabled by configure
-#ifdef WIN32
-  #define DLLIMPORT __declspec(dllimport)
-  #define DLLEXPORT __declspec(dllexport)
-  #define DLLLOCAL
-  #define DLLPUBLIC
-#else
-  #define DLLIMPORT
-  #ifdef GCC_HASCLASSVISIBILITY
-    #define DLLEXPORT __attribute__ ((visibility("default")))
-    #define DLLLOCAL __attribute__ ((visibility("hidden")))
-    #define DLLPUBLIC __attribute__ ((visibility("default")))
-  #else
-    #define DLLEXPORT
-    #define DLLLOCAL
-    #define DLLPUBLIC
-  #endif
-#endif
-		])
+		AC_DEFINE([DLLIMPORT],[/* intentionally left with no value */])
+		AC_DEFINE([DLLEXPORT],[__attribute__ ((visibility("default")))])
+		AC_DEFINE([DLLLOCAL],[__attribute__ ((visibility("hidden")))])
+		AC_DEFINE([DLLPUBLIC],[__attribute__ ((visibility("default")))])
+
 		AC_CHECK_CXXFLAG([fvisibility=hidden])
 		AC_CHECK_CXXFLAG([fvisibility-inlines-hidden])
 	],[
 		AC_MSG_RESULT([no])
-		AH_VERBATIM([DLLEXPORT],[
-// Proper DSO visibility is unsupported
-#define DLLIMPORT
-#define DLLEXPORT
-#define DLLLOCAL
-#define DLLPUBLIC
-		])
+		AC_DEFINE([DLLIMPORT],[/* unsupported */])
+		AC_DEFINE([DLLEXPORT],[/* unsupported */])
+		AC_DEFINE([DLLLOCAL],[/* unsupported */])
+		AC_DEFINE([DLLPUBLIC],[/* unsupported */])
 ])
 AC_LANG_POP
 
diff --git a/distro/gentoo/sgpemv2-0.00.ebuild b/distro/gentoo/sgpemv2-0.00.ebuild
new file mode 100644
index 0000000..ce6022e
--- /dev/null
+++ b/distro/gentoo/sgpemv2-0.00.ebuild
@@ -0,0 +1,16 @@
+# Copyright 1999-2006 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+# $Header: $
+
+DESCRIPTION=""
+HOMEPAGE=""
+SRC_URI=""
+
+LICENSE=""
+SLOT="0"
+KEYWORDS="~x86"
+IUSE=""
+
+DEPEND=""
+RDEPEND=""
+
diff --git a/src/backend/Makefile.am b/src/backend/Makefile.am
index 0cbec0f..36d6377 100644
--- a/src/backend/Makefile.am
+++ b/src/backend/Makefile.am
@@ -44,12 +44,8 @@ libbackend_la_LIBADD = $(PYTHON_LDFLAGS) \
 libbackend_la_LDFLAGS = $(PYTHON_EXTRA_LDFLAGS)
 
 # Please keep this in sorted order:
-libbackend_la_SOURCES = empty.cc
-
-noinst_HEADERS = 
-
-# !! temp file for debug, will be deleted as soon as 
-# !! source's in place
-empty.cc :
-	echo "int main() {}" > @builddir@/$@
+libbackend_la_SOURCES = \
+		schedulable.cc
 
+noinst_HEADERS = \
+		schedulable.hh
diff --git a/src/backend/schedulable.cc b/src/backend/schedulable.cc
new file mode 100644
index 0000000..a9095e7
--- /dev/null
+++ b/src/backend/schedulable.cc
@@ -0,0 +1,55 @@
+// src/backend/schedulable.cc - Copyright 2005, 2006, University
+//               of Padova, dept. of Pure and Applied
+//               Mathematics
+//
+// This file is part of SGPEMv2.
+//
+// This is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// SGPEMv2 is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with SGPEMv2; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+#include "schedulable.hh"
+using namespace sgpem;
+
+
+Schedulable::Schedulable(unsigned int arrival, 
+			 unsigned int total, 
+			 int priority) :
+  _arrival_time(arrival), _total_time(total), _priority(priority) 
+{}
+
+
+Schedulable::~Schedulable() 
+{}
+
+
+unsigned int
+Schedulable::getArrivalTime() const 
+{
+  return _arrival_time;
+}
+
+
+unsigned int 
+Schedulable::getTotalCPUTime() const 
+{
+  return _total_time;
+}
+
+
+int 
+Schedulable::getPriority() const 
+{
+  return _priority;
+}
+
diff --git a/src/backend/schedulable.hh b/src/backend/schedulable.hh
new file mode 100644
index 0000000..5960d84
--- /dev/null
+++ b/src/backend/schedulable.hh
@@ -0,0 +1,55 @@
+// src/backend/schedulable.hh - Copyright 2005, 2006, University
+//               of Padova, dept. of Pure and Applied
+//               Mathematics
+//
+// This file is part of SGPEMv2.
+//
+// This is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// SGPEMv2 is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with SGPEMv2; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+#ifndef SCHEDULABLE_HH
+#define SCHEDULABLE_HH 1
+
+#include "config.h"
+
+namespace sgpem
+{
+  class Schedulable;
+
+  /** \brief An entity that can use the processor
+   *  This abstract class describes an entity that can use the 
+   *  processor. It describes the parameters that don't change 
+   *  during a simulation.
+   *  All subclasses are ... (FIXME: teach Luca and Marco what's 
+   *  the Italian language for, damn them! -- they must have 
+   *  *smoked* mushrooms! :-) ) */
+  class DLLEXPORT Schedulable 
+  {
+  public:
+    Schedulable(unsigned int arrival, unsigned int total, int priority);
+    virtual ~Schedulable() = 0;
+    
+    virtual unsigned int getArrivalTime()  const;
+    unsigned int getTotalCPUTime() const;
+    int getPriority() const;
+    
+  private:
+    unsigned int _arrival_time;
+    unsigned int _total_time;
+    int          _priority;
+  };
+    
+}
+
+#endif
diff --git a/src/main.hh b/src/main.hh
index 438acd7..afa26fd 100644
--- a/src/main.hh
+++ b/src/main.hh
@@ -1,4 +1,4 @@
-// src/main.cc - Copyright 2005, 2006, University
+// src/main.hh - Copyright 2005, 2006, University
 //               of Padova, dept. of Pure and Applied
 //               Mathematics
 //
@@ -21,7 +21,4 @@
 #ifndef MAIN_HH
 #define MAIN_HH 1
 
-// found in mainwindow.hh
-extern void build_gui(int argc, char** argv);
-
 #endif
diff --git a/src/startgui.cc b/src/startgui.cc
index df75b3b..d153b55 100644
--- a/src/startgui.cc
+++ b/src/startgui.cc
@@ -26,11 +26,10 @@
 
 #include <gtkmm/main.h>
 
-void DLLEXPORT
+void
 start_gui(int argc, char** argv) 
 {
   Gtk::Main gtk_main(argc,argv);
   MainWindow main_window;
   Gtk::Main::run(main_window);
 }
-