--- a/graal/com.oracle.graal.compiler/src/com/oracle/graal/compiler/GraalOptions.java	Fri Mar 23 12:13:04 2012 -0700
+++ b/graal/com.oracle.graal.compiler/src/com/oracle/graal/compiler/GraalOptions.java	Mon Mar 26 13:49:13 2012 +0200
@@ -196,6 +196,11 @@
      */
     public static boolean AllocSSA                           = false;
 
+    /**
+     * Prints all the available GraalOptions.
+     */
+    public static boolean PrintFlags                           = false;
+
     static {
         // turn detailed assertions on when the general assertions are on (misusing the assert keyword for this)
         assert (DetailedAsserts = true) == true;

--- a/graal/com.oracle.graal.hotspot/src/com/oracle/graal/hotspot/HotSpotOptions.java	Fri Mar 23 12:13:04 2012 -0700
+++ b/graal/com.oracle.graal.hotspot/src/com/oracle/graal/hotspot/HotSpotOptions.java	Mon Mar 26 13:49:13 2012 +0200
@@ -24,6 +24,7 @@
 package com.oracle.graal.hotspot;
 
 import java.lang.reflect.*;
+import java.util.*;
 
 import com.oracle.graal.compiler.*;
 import com.oracle.graal.hotspot.logging.*;
@@ -35,6 +36,7 @@
         GraalOptions.ResolveClassBeforeStaticInvoke = false;
     }
 
+    // Called from VM code
     public static boolean setOption(String option) {
         if (option.length() == 0) {
             return false;
@@ -62,28 +64,35 @@
         Field f;
         try {
             f = GraalOptions.class.getDeclaredField(fieldName);
+            Class< ? > fType = f.getType();
 
             if (value == null) {
-                if (f.getType() == Float.TYPE) {
+                if (fType == Boolean.TYPE) {
+                    Logger.info("Value for boolean option '" + fieldName + "' must use '-G:+" + fieldName + "' or '-G:-" + fieldName + "' format");
+                    return false;
+                }
+
+                if (valueString == null) {
+                    Logger.info("Value for option '" + fieldName + "' must use '-G:" + fieldName + "=<value>' format");
+                    return false;
+                }
+
+                if (fType == Float.TYPE) {
                     value = Float.parseFloat(valueString);
-                } else if (f.getType() == Double.TYPE) {
+                } else if (fType == Double.TYPE) {
                     value = Double.parseDouble(valueString);
-                } else if (f.getType() == Integer.TYPE) {
+                } else if (fType == Integer.TYPE) {
                     value = Integer.parseInt(valueString);
-                } else if (f.getType() == Boolean.TYPE) {
-                    if (valueString == null || valueString.length() == 0) {
-                        value = true;
-                    } else {
-                        value = Boolean.parseBoolean(valueString);
-                    }
-                } else if (f.getType() == String.class) {
-                    if (valueString == null) {
-                        value = "";
-                    } else {
-                        value = valueString;
-                    }
+                } else if (fType == String.class) {
+                    value = valueString;
+                }
+            } else {
+                if (fType != Boolean.TYPE) {
+                    Logger.info("Value for option '" + fieldName + "' must use '-G:" + fieldName + "=<value>' format");
+                    return false;
                 }
             }
+
             if (value != null) {
                 f.setAccessible(true);
                 f.set(null, value);
@@ -106,6 +115,31 @@
             return false;
         }
 
+        if (option.equals("+PrintFlags")) {
+            printFlags();
+        }
+
         return true;
     }
+
+    private static void printFlags() {
+        Logger.info("[Graal flags]");
+        Field[] flags = GraalOptions.class.getDeclaredFields();
+        Arrays.sort(flags, new Comparator<Field>() {
+            public int compare(Field o1, Field o2) {
+                return o1.getName().compareTo(o2.getName());
+            }
+        });
+        for (Field f : flags) {
+            if (Modifier.isPublic(f.getModifiers()) && Modifier.isStatic(f.getModifiers())) {
+                f.setAccessible(true);
+                try {
+                    Object value = f.get(null);
+                    Logger.info(String.format("%9s %-40s = %s", f.getType().getSimpleName(), f.getName(), value));
+                } catch (Exception e) {
+                }
+            }
+        }
+        System.exit(0);
+    }
 }

--- a/src/share/vm/graal/graalCompiler.cpp	Fri Mar 23 12:13:04 2012 -0700
+++ b/src/share/vm/graal/graalCompiler.cpp	Mon Mar 26 13:49:13 2012 +0200
@@ -80,7 +80,7 @@
       Handle option = java_lang_String::create_from_str(arg, THREAD);
       jboolean result = VMToCompiler::setOption(option);
       if (!result) {
-        tty->print_cr("Invalid option for graal!");
+        tty->print_cr("Invalid option for graal: -G:%s", arg);
         vm_abort(false);
       }
     }