Fix http://dartbug.com/9137 :

runtime/vm/flags.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flags.h"
 
 #include "platform/assert.h"
 #include "vm/os.h"
 
 namespace dart {
@@ skipping 84 matching lines @@
     cur = cur->next_;
   }
   return NULL;
 }
 
 
 bool Flags::Register_bool(bool* addr,
                           const char* name,
                           bool default_value,
                           const char* comment) {
-  ASSERT(Lookup(name) == NULL);
-
-  Flag* flag = new Flag(name, comment, addr, Flag::kBoolean);
+  Flag* flag = Lookup(name);
+  if (flag != NULL) {
+    ASSERT(flag->IsUnrecognized());
+    return default_value;

[siva, 2013/04/05 07:14:28]

nobody seems to use the return value from this function, why does it return the
default_value?

[Ivan Posva, 2013/04/22 12:59:27]

It is used in flags.h:

#define DEFINE_FLAG(type, name, default_value, comment) \
  type FLAG_##name = Flags::Register_##type(&FLAG_##name, #name, default_value,
comment)

+  }
+  flag = new Flag(name, comment, addr, Flag::kBoolean);
   flag->next_ = Flags::flags_;
   Flags::flags_ = flag;
 
   return default_value;
 }
 
 
 int Flags::Register_int(int* addr,
                         const char* name,
                         int default_value,
@@ skipping 76 matching lines @@
   intptr_t name_len = equals - option;
   char* name = new char[name_len + 1];
   strncpy(name, option, name_len);
   name[name_len] = '\0';
   Normalize(name);
 
   Flag* flag = Flags::Lookup(name);
   if (flag == NULL) {
     // Collect unrecognized flags.
     char* new_flag = new char[name_len + 1];
-    strncpy(new_flag, name, name_len);
+    strncpy(new_flag, option, name_len);
     new_flag[name_len] = '\0';
     Flags::Register_bool(NULL, new_flag, true, NULL);
   } else {
     // Only set values for recognized flags, skip collected
     // unrecognized flags.
     if (!flag->IsUnrecognized()) {
       switch (flag->type_) {
         case Flag::kBoolean: {
           if (strcmp(argument, "true") == 0) {
             *flag->bool_ptr_ = true;
@@ skipping 114 matching lines @@
     }
 
     qsort(flag_array, num_flags, sizeof flag_array[0], CompareFlagNames);
 
     for (int i = 0; i < num_flags; ++i) {
       flag_array[i]->Print();
     }
     delete[] flag_array;
   }
 }  // namespace dart