52   address   cursp = (address)sp();

    52   address sp = (address)_sp;

    53   address   curfp = (address)fp();

    53   address fp = (address)_fp;

    54   if ((cursp != NULL && curfp != NULL &&

    54   address unextended_sp = (address)_unextended_sp;

    55       (cursp <= thread->stack_base() && cursp >= thread->stack_base() - thread->stack_size())) &&

    55 

    56       (curfp <= thread->stack_base() && curfp >= thread->stack_base() - thread->stack_size())) {

    56   // Consider stack guards when trying to determine "safe" stack pointers

    57       safe = true;

    57   static size_t stack_guard_size = os::uses_stack_guard_pages() ?

    58   }

    58     JavaThread::stack_red_zone_size() + JavaThread::stack_yellow_reserved_zone_size() : 0;

    59   return safe;

    59   size_t usable_stack_size = thread->stack_size() - stack_guard_size;

    60 

    61   // sp must be within the usable part of the stack (not in guards)

    62   bool sp_safe = (sp < thread->stack_base()) &&

    63                  (sp >= thread->stack_base() - usable_stack_size);

    64 

    65 

    66   if (!sp_safe) {

    67     return false;

    68   }

    69 

    70   // Unextended sp must be within the stack and above or equal sp

    71   bool unextended_sp_safe = (unextended_sp < thread->stack_base()) && (unextended_sp >= sp);

    72 

    73   if (!unextended_sp_safe) {

    74     return false;

    75   }

    76 

    77   // An fp must be within the stack and above (but not equal) sp.

    78   bool fp_safe = (fp <= thread->stack_base()) &&  (fp > sp);

    79   // an interpreter fp must be within the stack and above (but not equal) sp

    80   bool fp_interp_safe = (fp <= thread->stack_base()) &&  (fp > sp) &&

    81     ((fp - sp) >= (ijava_state_size + top_ijava_frame_abi_size));

    82 

    83   // We know sp/unextended_sp are safe, only fp is questionable here

    84 

    85   // If the current frame is known to the code cache then we can attempt to

    86   // to construct the sender and do some validation of it. This goes a long way

    87   // toward eliminating issues when we get in frame construction code

    88 

    89   if (_cb != NULL ){

    90     // Entry frame checks

    91     if (is_entry_frame()) {

    92       // An entry frame must have a valid fp.

    93       return fp_safe && is_entry_frame_valid(thread);

    94     }

    95 

    96     // Now check if the frame is complete and the test is

    97     // reliable. Unfortunately we can only check frame completeness for

    98     // runtime stubs and nmethods. Other generic buffer blobs are more

    99     // problematic so we just assume they are OK. Adapter blobs never have a

   100     // complete frame and are never OK

   101     if (!_cb->is_frame_complete_at(_pc)) {

   102       if (_cb->is_compiled() || _cb->is_adapter_blob() || _cb->is_runtime_stub()) {

   103         return false;

   104       }

   105     }

   106 

   107     // Could just be some random pointer within the codeBlob.

   108     if (!_cb->code_contains(_pc)) {

   109       return false;

   110     }

   111 

   112     if (is_interpreted_frame() && !fp_interp_safe) {

   113       return false;

   114     }

   115 

   116     abi_minframe* sender_abi = (abi_minframe*) fp;

   117     intptr_t* sender_sp = (intptr_t*) fp;

   118     address   sender_pc = (address) sender_abi->lr;;

   119 

   120     // We must always be able to find a recognizable pc.

   121     CodeBlob* sender_blob = CodeCache::find_blob_unsafe(sender_pc);

   122     if (sender_blob == NULL) {

   123       return false;

   124     }

   125 

   126     // Could be a zombie method

   127     if (sender_blob->is_zombie() || sender_blob->is_unloaded()) {

   128       return false;

   129     }

   130 

   131     // It should be safe to construct the sender though it might not be valid.

   132 

   133     frame sender(sender_sp, sender_pc);

   134 

   135     // Do we have a valid fp?

   136     address sender_fp = (address) sender.fp();

   137 

   138     // sender_fp must be within the stack and above (but not

   139     // equal) current frame's fp.

   140     if (sender_fp > thread->stack_base() || sender_fp <= fp) {

   141         return false;

   142     }

   143 

   144     // If the potential sender is the interpreter then we can do some more checking.

   145     if (Interpreter::contains(sender_pc)) {

   146       return sender.is_interpreted_frame_valid(thread);

   147     }

   148 

   149     // Could just be some random pointer within the codeBlob.

   150     if (!sender.cb()->code_contains(sender_pc)) {

   151       return false;

   152     }

   153 

   154     // We should never be able to see an adapter if the current frame is something from code cache.

   155     if (sender_blob->is_adapter_blob()) {

   156       return false;

   157     }

   158 

   159     if (sender.is_entry_frame()) {

   160       return sender.is_entry_frame_valid(thread);

   161     }

   162 

   163     // Frame size is always greater than zero. If the sender frame size is zero or less,

   164     // something is really weird and we better give up.

   165     if (sender_blob->frame_size() <= 0) {

   166       return false;

   167     }

   168 

   169     return true;

   170   }

   171 

   172   // Must be native-compiled frame. Since sender will try and use fp to find

   173   // linkages it must be safe

   174 

   175   if (!fp_safe) {

   176     return false;

   177   }

   178 

   179   return true;