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 /*

  * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code 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

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

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  */

 #include "precompiled.hpp"

 #include "interpreter/interpreter.hpp"

 #include "memory/resourceArea.hpp"

 #include "oops/markOop.hpp"

 #include "oops/method.hpp"

 #include "oops/oop.inline.hpp"

 #include "prims/methodHandles.hpp"

 #include "runtime/frame.inline.hpp"

 #include "runtime/handles.inline.hpp"

 #include "runtime/javaCalls.hpp"

 #include "runtime/monitorChunk.hpp"

 #include "runtime/os.hpp"

 #include "runtime/signature.hpp"

 #include "runtime/stubCodeGenerator.hpp"

 #include "runtime/stubRoutines.hpp"

 #include "vmreg_x86.inline.hpp"

 #ifdef COMPILER1

 #include "c1/c1_Runtime1.hpp"

 #include "runtime/vframeArray.hpp"

 #endif

 #ifdef ASSERT

 void RegisterMap::check_location_valid() {

 }

 #endif

 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC

 // Profiling/safepoint support

 bool frame::safe_for_sender(JavaThread *thread) {

   address   sp = (address)_sp;

   address   fp = (address)_fp;

   address   unextended_sp = (address)_unextended_sp;

   // consider stack guards when trying to determine "safe" stack pointers

   static size_t stack_guard_size = os::uses_stack_guard_pages() ? (StackYellowPages + StackRedPages) * os::vm_page_size() : 0;

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

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

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

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

   if (!sp_safe) {

     return false;

   }

   // unextended sp must be within the stack and above or equal sp

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

                             (unextended_sp >= sp);

   if (!unextended_sp_safe) {

     return false;

   }

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

   // second evaluation on fp+ is added to handle situation where fp is -1

   bool fp_safe = (fp < thread->stack_base() && (fp > sp) && (((fp + (return_addr_offset * sizeof(void*))) < thread->stack_base())));

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

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

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

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

   if (_cb != NULL ) {

     // First check if frame is complete and tester is reliable

     // Unfortunately we can only check frame complete for runtime stubs and nmethod

     // other generic buffer blobs are more problematic so we just assume they are

     // ok. adapter blobs never have a frame complete and are never ok.

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

       if (_cb->is_nmethod() || _cb->is_adapter_blob() || _cb->is_runtime_stub()) {

         return false;

       }

     }

     // Could just be some random pointer within the codeBlob

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

       return false;

     }

     // Entry frame checks

     if (is_entry_frame()) {

       // an entry frame must have a valid fp.

       if (!fp_safe) return false;

       // Validate the JavaCallWrapper an entry frame must have

       address jcw = (address)entry_frame_call_wrapper();

       bool jcw_safe = (jcw < thread->stack_base()) && ( jcw > fp);

       return jcw_safe;

     }

     intptr_t* sender_sp = NULL;

     address   sender_pc = NULL;

     if (is_interpreted_frame()) {

       // fp must be safe

       if (!fp_safe) {

         return false;

       }

       sender_pc = (address) this->fp()[return_addr_offset];

       sender_sp = (intptr_t*) addr_at(sender_sp_offset);

     } else {

       // must be some sort of compiled/runtime frame

       // fp does not have to be safe (although it could be check for c1?)

       // check for a valid frame_size, otherwise we are unlikely to get a valid sender_pc

       if (_cb->frame_size() <= 0) {

         return false;

       }

       sender_sp = _unextended_sp + _cb->frame_size();

       // On Intel the return_address is always the word on the stack

       sender_pc = (address) *(sender_sp-1);

     }

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

     if (Interpreter::contains(sender_pc)) {

       // ebp is always saved in a recognizable place in any code we generate. However

       // only if the sender is interpreted/call_stub (c1 too?) are we certain that the saved ebp

       // is really a frame pointer.

       intptr_t *saved_fp = (intptr_t*)*(sender_sp - frame::sender_sp_offset);

       bool saved_fp_safe = ((address)saved_fp < thread->stack_base()) && (saved_fp > sender_sp);

       if (!saved_fp_safe) {

         return false;

       }

       // construct the potential sender

       frame sender(sender_sp, saved_fp, sender_pc);

       return sender.is_interpreted_frame_valid(thread);

     }

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

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

     if (sender_pc == NULL ||  sender_blob == NULL) {

       return false;

     }

     // Could be a zombie method

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

       return false;

     }

     // Could just be some random pointer within the codeBlob

     if (!sender_blob->code_contains(sender_pc)) {

       return false;

     }

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

     if (sender_blob->is_adapter_blob()) {

       return false;

     }

     // Could be the call_stub

     if (StubRoutines::returns_to_call_stub(sender_pc)) {

       intptr_t *saved_fp = (intptr_t*)*(sender_sp - frame::sender_sp_offset);

       bool saved_fp_safe = ((address)saved_fp < thread->stack_base()) && (saved_fp > sender_sp);

       if (!saved_fp_safe) {

         return false;

       }

       // construct the potential sender

       frame sender(sender_sp, saved_fp, sender_pc);

       // Validate the JavaCallWrapper an entry frame must have

       address jcw = (address)sender.entry_frame_call_wrapper();

       bool jcw_safe = (jcw < thread->stack_base()) && ( jcw > (address)sender.fp());

       return jcw_safe;

     }

     if (sender_blob->is_nmethod()) {

         nmethod* nm = sender_blob->as_nmethod_or_null();

         if (nm != NULL) {

             if (nm->is_deopt_mh_entry(sender_pc) || nm->is_deopt_entry(sender_pc) ||

                 nm->method()->is_method_handle_intrinsic()) {

                 return false;

             }

         }

     }

     // If the frame size is 0 something (or less) is bad because every nmethod has a non-zero frame size

     // because the return address counts against the callee's frame.

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

       assert(!sender_blob->is_nmethod(), "should count return address at least");

       return false;

     }

     // We should never be able to see anything here except an nmethod. If something in the

     // code cache (current frame) is called by an entity within the code cache that entity

     // should not be anything but the call stub (already covered), the interpreter (already covered)

     // or an nmethod.

     if (!sender_blob->is_nmethod()) {

         return false;

     }

     // Could put some more validation for the potential non-interpreted sender

     // frame we'd create by calling sender if I could think of any. Wait for next crash in forte...

     // One idea is seeing if the sender_pc we have is one that we'd expect to call to current cb

     // We've validated the potential sender that would be created

     return true;

   }

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

   // linkages it must be safe

   if (!fp_safe) {

     return false;

   }

   // Will the pc we fetch be non-zero (which we'll find at the oldest frame)

   if ( (address) this->fp()[return_addr_offset] == NULL) return false;

   // could try and do some more potential verification of native frame if we could think of some...

   return true;

 }

 void frame::patch_pc(Thread* thread, address pc) {

   address* pc_addr = &(((address*) sp())[-1]);

   if (TracePcPatching) {

     tty->print_cr("patch_pc at address " INTPTR_FORMAT " [" INTPTR_FORMAT " -> " INTPTR_FORMAT "]",

                   pc_addr, *pc_addr, pc);

   }

   // Either the return address is the original one or we are going to

   // patch in the same address that's already there.

   assert(_pc == *pc_addr || pc == *pc_addr, "must be");

   *pc_addr = pc;

   _cb = CodeCache::find_blob(pc);

   address original_pc = nmethod::get_deopt_original_pc(this);

   if (original_pc != NULL) {

     assert(original_pc == _pc, "expected original PC to be stored before patching");

     _deopt_state = is_deoptimized;

     // leave _pc as is

   } else {

     _deopt_state = not_deoptimized;

     _pc = pc;

   }

 }

 bool frame::is_interpreted_frame() const  {

   return Interpreter::contains(pc());

 }

 int frame::frame_size(RegisterMap* map) const {

   frame sender = this->sender(map);

   return sender.sp() - sp();

 }

 intptr_t* frame::entry_frame_argument_at(int offset) const {

   // convert offset to index to deal with tsi

   int index = (Interpreter::expr_offset_in_bytes(offset)/wordSize);

   // Entry frame's arguments are always in relation to unextended_sp()

   return &unextended_sp()[index];

 }

 // sender_sp

 #ifdef CC_INTERP

 intptr_t* frame::interpreter_frame_sender_sp() const {

   assert(is_interpreted_frame(), "interpreted frame expected");

   // QQQ why does this specialize method exist if frame::sender_sp() does same thing?

   // seems odd and if we always know interpreted vs. non then sender_sp() is really

   // doing too much work.

   return get_interpreterState()->sender_sp();

 }

 // monitor elements

 BasicObjectLock* frame::interpreter_frame_monitor_begin() const {

   return get_interpreterState()->monitor_base();

 }

 BasicObjectLock* frame::interpreter_frame_monitor_end() const {

   return (BasicObjectLock*) get_interpreterState()->stack_base();

 }

 #else // CC_INTERP

 intptr_t* frame::interpreter_frame_sender_sp() const {

   assert(is_interpreted_frame(), "interpreted frame expected");

   return (intptr_t*) at(interpreter_frame_sender_sp_offset);

 }

 void frame::set_interpreter_frame_sender_sp(intptr_t* sender_sp) {

   assert(is_interpreted_frame(), "interpreted frame expected");

   ptr_at_put(interpreter_frame_sender_sp_offset, (intptr_t) sender_sp);

 }

 // monitor elements

 BasicObjectLock* frame::interpreter_frame_monitor_begin() const {

   return (BasicObjectLock*) addr_at(interpreter_frame_monitor_block_bottom_offset);

 }

 BasicObjectLock* frame::interpreter_frame_monitor_end() const {

   BasicObjectLock* result = (BasicObjectLock*) *addr_at(interpreter_frame_monitor_block_top_offset);

   // make sure the pointer points inside the frame

   assert(sp() <= (intptr_t*) result, "monitor end should be above the stack pointer");

   assert((intptr_t*) result < fp(),  "monitor end should be strictly below the frame pointer");

   return result;

 }

 void frame::interpreter_frame_set_monitor_end(BasicObjectLock* value) {

   *((BasicObjectLock**)addr_at(interpreter_frame_monitor_block_top_offset)) = value;

 }

 // Used by template based interpreter deoptimization

 void frame::interpreter_frame_set_last_sp(intptr_t* sp) {

     *((intptr_t**)addr_at(interpreter_frame_last_sp_offset)) = sp;

 }

 #endif // CC_INTERP

 frame frame::sender_for_entry_frame(RegisterMap* map) const {

   assert(map != NULL, "map must be set");

   // Java frame called from C; skip all C frames and return top C

   // frame of that chunk as the sender

   JavaFrameAnchor* jfa = entry_frame_call_wrapper()->anchor();

   assert(!entry_frame_is_first(), "next Java fp must be non zero");

   assert(jfa->last_Java_sp() > sp(), "must be above this frame on stack");

   // Since we are walking the stack now this nested anchor is obviously walkable

   // even if it wasn't when it was stacked.

   if (!jfa->walkable()) {

     // Capture _last_Java_pc (if needed) and mark anchor walkable.

     jfa->capture_last_Java_pc();

   }

   map->clear();

   assert(map->include_argument_oops(), "should be set by clear");

   assert(jfa->last_Java_pc() != NULL, "not walkable");

   frame fr(jfa->last_Java_sp(), jfa->last_Java_fp(), jfa->last_Java_pc());

   return fr;

 }

 //------------------------------------------------------------------------------

 // frame::verify_deopt_original_pc

 //

 // Verifies the calculated original PC of a deoptimization PC for the

 // given unextended SP.

 #ifdef ASSERT

 void frame::verify_deopt_original_pc(nmethod* nm, intptr_t* unextended_sp) {

   frame fr;

   // This is ugly but it's better than to change {get,set}_original_pc

   // to take an SP value as argument.  And it's only a debugging

   // method anyway.

   fr._unextended_sp = unextended_sp;

   address original_pc = nm->get_original_pc(&fr);

   assert(nm->insts_contains(original_pc), "original PC must be in nmethod");

 }

 #endif

 //------------------------------------------------------------------------------

 // frame::adjust_unextended_sp

 void frame::adjust_unextended_sp() {

   // On x86, sites calling method handle intrinsics and lambda forms are treated

   // as any other call site. Therefore, no special action is needed when we are

   // returning to any of these call sites.

   nmethod* sender_nm = (_cb == NULL) ? NULL : _cb->as_nmethod_or_null();

   if (sender_nm != NULL) {

     // If the sender PC is a deoptimization point, get the original PC.

     if (sender_nm->is_deopt_entry(_pc) ||

         sender_nm->is_deopt_mh_entry(_pc)) {

       DEBUG_ONLY(verify_deopt_original_pc(sender_nm, _unextended_sp));

     }

   }

 }

 //------------------------------------------------------------------------------

 // frame::update_map_with_saved_link

 void frame::update_map_with_saved_link(RegisterMap* map, intptr_t** link_addr) {

   // The interpreter and compiler(s) always save EBP/RBP in a known

   // location on entry. We must record where that location is

   // so this if EBP/RBP was live on callout from c2 we can find

   // the saved copy no matter what it called.

   // Since the interpreter always saves EBP/RBP if we record where it is then

   // we don't have to always save EBP/RBP on entry and exit to c2 compiled

   // code, on entry will be enough.

   map->set_location(rbp->as_VMReg(), (address) link_addr);

 #ifdef AMD64

   // this is weird "H" ought to be at a higher address however the

   // oopMaps seems to have the "H" regs at the same address and the

   // vanilla register.

   // XXXX make this go away

   if (true) {

     map->set_location(rbp->as_VMReg()->next(), (address) link_addr);

   }

 #endif // AMD64

 }

 //------------------------------------------------------------------------------

 // frame::sender_for_interpreter_frame

 frame frame::sender_for_interpreter_frame(RegisterMap* map) const {

   // SP is the raw SP from the sender after adapter or interpreter

   // extension.

   intptr_t* sender_sp = this->sender_sp();

   // This is the sp before any possible extension (adapter/locals).

   intptr_t* unextended_sp = interpreter_frame_sender_sp();

 #ifdef COMPILER2

   if (map->update_map()) {

     update_map_with_saved_link(map, (intptr_t**) addr_at(link_offset));

   }

 #endif // COMPILER2

   return frame(sender_sp, unextended_sp, link(), sender_pc());

 }

 //------------------------------------------------------------------------------

 // frame::sender_for_compiled_frame

 frame frame::sender_for_compiled_frame(RegisterMap* map) const {

   assert(map != NULL, "map must be set");

   // frame owned by optimizing compiler

   assert(_cb->frame_size() >= 0, "must have non-zero frame size");

   intptr_t* sender_sp = unextended_sp() + _cb->frame_size();

   intptr_t* unextended_sp = sender_sp;

   // On Intel the return_address is always the word on the stack

   address sender_pc = (address) *(sender_sp-1);

   // This is the saved value of EBP which may or may not really be an FP.

   // It is only an FP if the sender is an interpreter frame (or C1?).

   intptr_t** saved_fp_addr = (intptr_t**) (sender_sp - frame::sender_sp_offset);

   if (map->update_map()) {

     // Tell GC to use argument oopmaps for some runtime stubs that need it.

     // For C1, the runtime stub might not have oop maps, so set this flag

     // outside of update_register_map.

     map->set_include_argument_oops(_cb->caller_must_gc_arguments(map->thread()));

     if (_cb->oop_maps() != NULL) {

       OopMapSet::update_register_map(this, map);

     }

     // Since the prolog does the save and restore of EBP there is no oopmap

     // for it so we must fill in its location as if there was an oopmap entry

     // since if our caller was compiled code there could be live jvm state in it.

     update_map_with_saved_link(map, saved_fp_addr);

   }

   assert(sender_sp != sp(), "must have changed");

   return frame(sender_sp, unextended_sp, *saved_fp_addr, sender_pc);

 }

 //------------------------------------------------------------------------------

 // frame::sender

 frame frame::sender(RegisterMap* map) const {

   // Default is we done have to follow them. The sender_for_xxx will

   // update it accordingly

   map->set_include_argument_oops(false);

   if (is_entry_frame())       return sender_for_entry_frame(map);

   if (is_interpreted_frame()) return sender_for_interpreter_frame(map);

   assert(_cb == CodeCache::find_blob(pc()),"Must be the same");

   if (_cb != NULL) {

     return sender_for_compiled_frame(map);

   }

   // Must be native-compiled frame, i.e. the marshaling code for native

   // methods that exists in the core system.

   return frame(sender_sp(), link(), sender_pc());

 }

 bool frame::interpreter_frame_equals_unpacked_fp(intptr_t* fp) {

   assert(is_interpreted_frame(), "must be interpreter frame");

   Method* method = interpreter_frame_method();

   // When unpacking an optimized frame the frame pointer is

   // adjusted with:

   int diff = (method->max_locals() - method->size_of_parameters()) *

              Interpreter::stackElementWords;

   return _fp == (fp - diff);

 }

 void frame::pd_gc_epilog() {

   // nothing done here now

 }

 bool frame::is_interpreted_frame_valid(JavaThread* thread) const {

 // QQQ

 #ifdef CC_INTERP

 #else

   assert(is_interpreted_frame(), "Not an interpreted frame");

   // These are reasonable sanity checks

   if (fp() == 0 || (intptr_t(fp()) & (wordSize-1)) != 0) {

     return false;

   }

   if (sp() == 0 || (intptr_t(sp()) & (wordSize-1)) != 0) {

     return false;

   }

   if (fp() + interpreter_frame_initial_sp_offset < sp()) {

     return false;

   }

   // These are hacks to keep us out of trouble.

   // The problem with these is that they mask other problems

   if (fp() <= sp()) {        // this attempts to deal with unsigned comparison above

     return false;

   }

   // do some validation of frame elements

   // first the method

   Method* m = *interpreter_frame_method_addr();

   // validate the method we'd find in this potential sender

   if (!m->is_valid_method()) return false;

   // stack frames shouldn't be much larger than max_stack elements

   if (fp() - sp() > 1024 + m->max_stack()*Interpreter::stackElementSize) {

     return false;

   }

   // validate bci/bcx

   intptr_t  bcx    = interpreter_frame_bcx();

   if (m->validate_bci_from_bcx(bcx) < 0) {

     return false;

   }

   // validate ConstantPoolCache*

   ConstantPoolCache* cp = *interpreter_frame_cache_addr();

   if (cp == NULL || !cp->is_metaspace_object()) return false;

   // validate locals

   address locals =  (address) *interpreter_frame_locals_addr();

   if (locals > thread->stack_base() || locals < (address) fp()) return false;

   // We'd have to be pretty unlucky to be mislead at this point

 #endif // CC_INTERP

   return true;

 }

 BasicType frame::interpreter_frame_result(oop* oop_result, jvalue* value_result) {

 #ifdef CC_INTERP

   // Needed for JVMTI. The result should always be in the

   // interpreterState object

   interpreterState istate = get_interpreterState();

 #endif // CC_INTERP

   assert(is_interpreted_frame(), "interpreted frame expected");

   Method* method = interpreter_frame_method();

   BasicType type = method->result_type();

   intptr_t* tos_addr;

   if (method->is_native()) {

     // Prior to calling into the runtime to report the method_exit the possible

     // return value is pushed to the native stack. If the result is a jfloat/jdouble

     // then ST0 is saved before EAX/EDX. See the note in generate_native_result

     tos_addr = (intptr_t*)sp();

     if (type == T_FLOAT || type == T_DOUBLE) {

     // QQQ seems like this code is equivalent on the two platforms

 #ifdef AMD64

       // This is times two because we do a push(ltos) after pushing XMM0

       // and that takes two interpreter stack slots.

       tos_addr += 2 * Interpreter::stackElementWords;

 #else

       tos_addr += 2;

 #endif // AMD64

     }

   } else {

     tos_addr = (intptr_t*)interpreter_frame_tos_address();

   }

   switch (type) {

     case T_OBJECT  :

     case T_ARRAY   : {

       oop obj;

       if (method->is_native()) {

 #ifdef CC_INTERP

         obj = istate->_oop_temp;

 #else

         obj = cast_to_oop(at(interpreter_frame_oop_temp_offset));

 #endif // CC_INTERP

       } else {

         oop* obj_p = (oop*)tos_addr;

         obj = (obj_p == NULL) ? (oop)NULL : *obj_p;

       }

       assert(obj == NULL || Universe::heap()->is_in(obj), "sanity check");

       *oop_result = obj;

       break;

     }

     case T_BOOLEAN : value_result->z = *(jboolean*)tos_addr; break;

     case T_BYTE    : value_result->b = *(jbyte*)tos_addr; break;

     case T_CHAR    : value_result->c = *(jchar*)tos_addr; break;

     case T_SHORT   : value_result->s = *(jshort*)tos_addr; break;

     case T_INT     : value_result->i = *(jint*)tos_addr; break;

     case T_LONG    : value_result->j = *(jlong*)tos_addr; break;

     case T_FLOAT   : {

 #ifdef AMD64

         value_result->f = *(jfloat*)tos_addr;

 #else

       if (method->is_native()) {

         jdouble d = *(jdouble*)tos_addr;  // Result was in ST0 so need to convert to jfloat

         value_result->f = (jfloat)d;

       } else {

         value_result->f = *(jfloat*)tos_addr;

       }

 #endif // AMD64

       break;

     }

     case T_DOUBLE  : value_result->d = *(jdouble*)tos_addr; break;

     case T_VOID    : /* Nothing to do */ break;

     default        : ShouldNotReachHere();

   }

   return type;

 }

 intptr_t* frame::interpreter_frame_tos_at(jint offset) const {

   int index = (Interpreter::expr_offset_in_bytes(offset)/wordSize);

   return &interpreter_frame_tos_address()[index];

 }

 #ifndef PRODUCT

 #define DESCRIBE_FP_OFFSET(name) \

   values.describe(frame_no, fp() + frame::name##_offset, #name)

 void frame::describe_pd(FrameValues& values, int frame_no) {

   if (is_interpreted_frame()) {

     DESCRIBE_FP_OFFSET(interpreter_frame_sender_sp);

     DESCRIBE_FP_OFFSET(interpreter_frame_last_sp);

     DESCRIBE_FP_OFFSET(interpreter_frame_method);

     DESCRIBE_FP_OFFSET(interpreter_frame_mdx);

     DESCRIBE_FP_OFFSET(interpreter_frame_cache);

     DESCRIBE_FP_OFFSET(interpreter_frame_locals);

     DESCRIBE_FP_OFFSET(interpreter_frame_bcx);

     DESCRIBE_FP_OFFSET(interpreter_frame_initial_sp);

   }

 }

 #endif

 intptr_t *frame::initial_deoptimization_info() {

   // used to reset the saved FP

   return fp();

 }

 intptr_t* frame::real_fp() const {

   if (_cb != NULL) {

     // use the frame size if valid

     int size = _cb->frame_size();

     if (size > 0) {

       return unextended_sp() + size;

     }

   }

   // else rely on fp()

   assert(! is_compiled_frame(), "unknown compiled frame size");

   return fp();

 }

 #ifndef PRODUCT

 // This is a generic constructor which is only used by pns() in debug.cpp.

 frame::frame(void* sp, void* fp, void* pc) {

   init((intptr_t*)sp, (intptr_t*)fp, (address)pc);

 }

 #endif

 void JavaFrameAnchor::make_walkable(JavaThread* thread) {

   // last frame set?

   if (last_Java_sp() == NULL) return;

   // already walkable?

   if (walkable()) return;

   assert(Thread::current() == (Thread*)thread, "not current thread");

   assert(last_Java_sp() != NULL, "not called from Java code?");

   assert(last_Java_pc() == NULL, "already walkable");

   capture_last_Java_pc();

   assert(walkable(), "something went wrong");

 }

 void JavaFrameAnchor::capture_last_Java_pc() {

   assert(_last_Java_sp != NULL, "no last frame set");

   assert(_last_Java_pc == NULL, "already walkable");

   _last_Java_pc = (address)_last_Java_sp[-1];

 }