Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 1997, 2012, 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.

  *

  */

 #include "precompiled.hpp"

 #include "classfile/stackMapTableFormat.hpp"

 #include "interpreter/bytecodes.hpp"

 #include "memory/oopFactory.hpp"

 #include "memory/universe.inline.hpp"

 #include "oops/oop.inline.hpp"

 #include "runtime/handles.inline.hpp"

 #include "runtime/relocator.hpp"

 #define MAX_METHOD_LENGTH  65535

 #define MAX_SHORT ((1 << 15) - 1)

 #define MIN_SHORT (- (1 << 15))

 // Encapsulates a code change request. There are 3 types.

 // General instruction, jump instruction, and table/lookup switches

 //

 class ChangeItem : public ResourceObj {

   int _bci;

  public:

    ChangeItem(int bci) { _bci = bci; }

    virtual bool handle_code_change(Relocator *r) = 0;

    // type info

    virtual bool is_widen()      { return false; }

    virtual bool is_jump_widen() { return false; }

    virtual bool is_switch_pad() { return false; }

    // accessors

    int bci()    { return _bci; }

    void relocate(int break_bci, int delta) { if (_bci > break_bci) { _bci += delta; } }

    virtual bool adjust(int bci, int delta) { return false; }

    // debug

    virtual void print() = 0;

 };

 class ChangeWiden : public ChangeItem {

   int              _new_ilen;    // New length of instruction at bci

   u_char*          _inst_buffer; // New bytecodes

  public:

   ChangeWiden(int bci, int new_ilen, u_char* inst_buffer) : ChangeItem(bci) {

     _new_ilen = new_ilen;

     _inst_buffer = inst_buffer;

   }

   // Callback to do instruction

   bool handle_code_change(Relocator *r) { return r->handle_widen(bci(), _new_ilen, _inst_buffer); };

   bool is_widen()              { return true; }

   void print()                 { tty->print_cr("ChangeWiden. bci: %d   New_ilen: %d", bci(), _new_ilen); }

 };

 class ChangeJumpWiden : public ChangeItem {

   int _delta;  // New length of instruction at bci

  public:

   ChangeJumpWiden(int bci, int delta) : ChangeItem(bci) { _delta = delta; }

   // Callback to do instruction

   bool handle_code_change(Relocator *r) { return r->handle_jump_widen(bci(), _delta); };

   bool is_jump_widen()         { return true; }

   // If the bci matches, adjust the delta in the change jump request.

   bool adjust(int jump_bci, int delta) {

     if (bci() == jump_bci) {

       if (_delta > 0)

         _delta += delta;

       else

         _delta -= delta;

       return true;

     }

     return false;

   }

   void print()                 { tty->print_cr("ChangeJumpWiden. bci: %d   Delta: %d", bci(), _delta); }

 };

 class ChangeSwitchPad : public ChangeItem {

   int  _padding;

   bool _is_lookup_switch;

  public:

    ChangeSwitchPad(int bci, int padding, bool is_lookup_switch) : ChangeItem(bci) {

      _padding = padding;

      _is_lookup_switch = is_lookup_switch;

    }

    // Callback to do instruction

    bool handle_code_change(Relocator *r) { return r->handle_switch_pad(bci(), _padding, _is_lookup_switch); };

    bool is_switch_pad()        { return true; }

    int  padding()              { return _padding;  }

    bool is_lookup_switch()     { return _is_lookup_switch; }

    void print()                { tty->print_cr("ChangeSwitchPad. bci: %d   Padding: %d  IsLookupSwitch: %d", bci(), _padding, _is_lookup_switch); }

 };

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

 // Relocator code

 Relocator::Relocator(methodHandle m, RelocatorListener* listener) {

   set_method(m);

   set_code_length(method()->code_size());

   set_code_array(NULL);

   // Allocate code array and copy bytecodes

   if (!expand_code_array(0)) {

     // Should have at least MAX_METHOD_LENGTH available or the verifier

     // would have failed.

     ShouldNotReachHere();

   }

   set_compressed_line_number_table(NULL);

   set_compressed_line_number_table_size(0);

   _listener = listener;

 }

 // size is the new size of the instruction at bci. Hence, if size is less than the current

 // instruction sice, we will shrink the code.

 methodHandle Relocator::insert_space_at(int bci, int size, u_char inst_buffer[], TRAPS) {

   _changes = new GrowableArray<ChangeItem*> (10);

   _changes->push(new ChangeWiden(bci, size, inst_buffer));

   if (TraceRelocator) {

     tty->print_cr("Space at: %d Size: %d", bci, size);

     _method->print();

     _method->print_codes();

     tty->print_cr("-------------------------------------------------");

   }

   if (!handle_code_changes()) return methodHandle();

     // Construct the new method

   methodHandle new_method = methodOopDesc::clone_with_new_data(method(),

                               code_array(), code_length(),

                               compressed_line_number_table(),

                               compressed_line_number_table_size(),

                               CHECK_(methodHandle()));

     set_method(new_method);

   if (TraceRelocator) {

     tty->print_cr("-------------------------------------------------");

     tty->print_cr("new method");

     _method->print_codes();

   }

   return new_method;

 }

 bool Relocator::handle_code_changes() {

   assert(_changes != NULL, "changes vector must be initialized");

   while (!_changes->is_empty()) {

     // Inv: everything is aligned.

     ChangeItem* ci = _changes->first();

     if (TraceRelocator) {

       ci->print();

     }

     // Execute operation

     if (!ci->handle_code_change(this)) return false;

     // Shuffel items up

     for (int index = 1; index < _changes->length(); index++) {

       _changes->at_put(index-1, _changes->at(index));

     }

     _changes->pop();

   }

   return true;

 }

 bool Relocator::is_opcode_lookupswitch(Bytecodes::Code bc) {

   switch (bc) {

     case Bytecodes::_tableswitch:       return false;

     case Bytecodes::_lookupswitch:                   // not rewritten on ia64

     case Bytecodes::_fast_linearswitch:              // rewritten _lookupswitch

     case Bytecodes::_fast_binaryswitch: return true; // rewritten _lookupswitch

     default: ShouldNotReachHere();

   }

   return true; // dummy

 }

 // We need a special instruction size method, since lookupswitches and tableswitches might not be

 // properly alligned during relocation

 int Relocator::rc_instr_len(int bci) {

   Bytecodes::Code bc= code_at(bci);

   switch (bc) {

     // In the case of switch instructions, see if we have the original

     // padding recorded.

     case Bytecodes::_tableswitch:

     case Bytecodes::_lookupswitch:

     case Bytecodes::_fast_linearswitch:

     case Bytecodes::_fast_binaryswitch:

     {

       int pad = get_orig_switch_pad(bci, is_opcode_lookupswitch(bc));

       if (pad == -1) {

         return instruction_length_at(bci);

       }

       // Otherwise, depends on the switch type.

       switch (bc) {

         case Bytecodes::_tableswitch: {

           int lo = int_at(bci + 1 + pad + 4 * 1);

           int hi = int_at(bci + 1 + pad + 4 * 2);

           int n = hi - lo + 1;

           return 1 + pad + 4*(3 + n);

         }

         case Bytecodes::_lookupswitch:

         case Bytecodes::_fast_linearswitch:

         case Bytecodes::_fast_binaryswitch: {

           int npairs = int_at(bci + 1 + pad + 4 * 1);

           return 1 + pad + 4*(2 + 2*npairs);

         }

         default:

           ShouldNotReachHere();

       }

     }

   }

   return instruction_length_at(bci);

 }

 // If a change item is recorded for "pc", with type "ct", returns the

 // associated padding, else -1.

 int Relocator::get_orig_switch_pad(int bci, bool is_lookup_switch) {

   for (int k = 0; k < _changes->length(); k++) {

     ChangeItem* ci = _changes->at(k);

     if (ci->is_switch_pad()) {

       ChangeSwitchPad* csp = (ChangeSwitchPad*)ci;

       if (csp->is_lookup_switch() == is_lookup_switch && csp->bci() == bci) {

         return csp->padding();

       }

     }

   }

   return -1;

 }

 // Push a ChangeJumpWiden if it doesn't already exist on the work queue,

 // otherwise adjust the item already there by delta.  The calculation for

 // new_delta is wrong for this because it uses the offset stored in the

 // code stream itself which wasn't fixed when item was pushed on the work queue.

 void Relocator::push_jump_widen(int bci, int delta, int new_delta) {

   for (int j = 0; j < _changes->length(); j++) {

     ChangeItem* ci = _changes->at(j);

     if (ci->adjust(bci, delta)) return;

   }

   _changes->push(new ChangeJumpWiden(bci, new_delta));

 }

 // The current instruction of "c" is a jump; one of its offset starts

 // at "offset" and is a short if "isShort" is "TRUE",

 // and an integer otherwise.  If the jump crosses "breakPC", change

 // the span of the jump by "delta".

 void Relocator::change_jump(int bci, int offset, bool is_short, int break_bci, int delta) {

   int bci_delta = (is_short) ? short_at(offset) : int_at(offset);

   int targ = bci + bci_delta;

   if ((bci <= break_bci && targ >  break_bci) ||

       (bci >  break_bci && targ <= break_bci)) {

     int new_delta;

     if (bci_delta > 0)

       new_delta = bci_delta + delta;

     else

       new_delta = bci_delta - delta;

     if (is_short && ((new_delta > MAX_SHORT) || new_delta < MIN_SHORT)) {

       push_jump_widen(bci, delta, new_delta);

     } else if (is_short) {

       short_at_put(offset, new_delta);

     } else {

       int_at_put(offset, new_delta);

     }

   }

 }

 // Changes all jumps crossing "break_bci" by "delta".  May enqueue things

 // on "rc->changes"

 void Relocator::change_jumps(int break_bci, int delta) {

   int bci = 0;

   Bytecodes::Code bc;

   // Now, adjust any affected instructions.

   while (bci < code_length()) {

     switch (bc= code_at(bci)) {

       case Bytecodes::_ifeq:

       case Bytecodes::_ifne:

       case Bytecodes::_iflt:

       case Bytecodes::_ifge:

       case Bytecodes::_ifgt:

       case Bytecodes::_ifle:

       case Bytecodes::_if_icmpeq:

       case Bytecodes::_if_icmpne:

       case Bytecodes::_if_icmplt:

       case Bytecodes::_if_icmpge:

       case Bytecodes::_if_icmpgt:

       case Bytecodes::_if_icmple:

       case Bytecodes::_if_acmpeq:

       case Bytecodes::_if_acmpne:

       case Bytecodes::_ifnull:

       case Bytecodes::_ifnonnull:

       case Bytecodes::_goto:

       case Bytecodes::_jsr:

         change_jump(bci, bci+1, true, break_bci, delta);

         break;

       case Bytecodes::_goto_w:

       case Bytecodes::_jsr_w:

         change_jump(bci, bci+1, false, break_bci, delta);

         break;

       case Bytecodes::_tableswitch:

       case Bytecodes::_lookupswitch:

       case Bytecodes::_fast_linearswitch:

       case Bytecodes::_fast_binaryswitch: {

         int recPad = get_orig_switch_pad(bci, (bc != Bytecodes::_tableswitch));

         int oldPad = (recPad != -1) ? recPad : align(bci+1) - (bci+1);

         if (bci > break_bci) {

           int new_bci = bci + delta;

           int newPad = align(new_bci+1) - (new_bci+1);

           // Do we need to check the padding?

           if (newPad != oldPad) {

             if (recPad == -1) {

               _changes->push(new ChangeSwitchPad(bci, oldPad, (bc != Bytecodes::_tableswitch)));

             }

           }

         }

         // Then the rest, which depend on the kind of switch.

         switch (bc) {

           case Bytecodes::_tableswitch: {

             change_jump(bci, bci +1 + oldPad, false, break_bci, delta);

             // We cannot use the Bytecode_tableswitch abstraction, since the padding might not be correct.

             int lo = int_at(bci + 1 + oldPad + 4 * 1);

             int hi = int_at(bci + 1 + oldPad + 4 * 2);

             int n = hi - lo + 1;

             for (int k = 0; k < n; k++) {

               change_jump(bci, bci +1 + oldPad + 4*(k+3), false, break_bci, delta);

             }

             // Special next-bci calculation here...

             bci += 1 + oldPad + (n+3)*4;

             continue;

           }

           case Bytecodes::_lookupswitch:

           case Bytecodes::_fast_linearswitch:

           case Bytecodes::_fast_binaryswitch: {

             change_jump(bci, bci +1 + oldPad, false, break_bci, delta);

             // We cannot use the Bytecode_lookupswitch abstraction, since the padding might not be correct.

             int npairs = int_at(bci + 1 + oldPad + 4 * 1);

             for (int k = 0; k < npairs; k++) {

               change_jump(bci, bci + 1 + oldPad + 4*(2 + 2*k + 1), false, break_bci, delta);

             }

             /* Special next-bci calculation here... */

             bci += 1 + oldPad + (2 + (npairs*2))*4;

             continue;

           }

           default:

             ShouldNotReachHere();

         }

       }

       default:

         break;

     }

     bci += rc_instr_len(bci);

   }

 }

 // The width of instruction at "pc" is changing by "delta".  Adjust the

 // exception table, if any, of "rc->mb".

 void Relocator::adjust_exception_table(int bci, int delta) {

   ExceptionTable table(_method());

   for (int index = 0; index < table.length(); index ++) {

     if (table.start_pc(index) > bci) {

       table.set_start_pc(index, table.start_pc(index) + delta);

       table.set_end_pc(index, table.end_pc(index) + delta);

     } else if (bci < table.end_pc(index)) {

       table.set_end_pc(index, table.end_pc(index) + delta);

     }

     if (table.handler_pc(index) > bci)

       table.set_handler_pc(index, table.handler_pc(index) + delta);

   }

 }

 // The width of instruction at "bci" is changing by "delta".  Adjust the line number table.

 void Relocator::adjust_line_no_table(int bci, int delta) {

   if (method()->has_linenumber_table()) {

     CompressedLineNumberReadStream  reader(method()->compressed_linenumber_table());

     CompressedLineNumberWriteStream writer(64);  // plenty big for most line number tables

     while (reader.read_pair()) {

       int adjustment = (reader.bci() > bci) ? delta : 0;

       writer.write_pair(reader.bci() + adjustment, reader.line());

     }

     writer.write_terminator();

     set_compressed_line_number_table(writer.buffer());

     set_compressed_line_number_table_size(writer.position());

   }

 }

 // The width of instruction at "bci" is changing by "delta".  Adjust the local variable table.

 void Relocator::adjust_local_var_table(int bci, int delta) {

   int localvariable_table_length = method()->localvariable_table_length();

   if (localvariable_table_length > 0) {

     LocalVariableTableElement* table = method()->localvariable_table_start();

     for (int i = 0; i < localvariable_table_length; i++) {

       u2 current_bci = table[i].start_bci;

       if (current_bci > bci) {

         table[i].start_bci = current_bci + delta;

       } else {

         u2 current_length = table[i].length;

         if (current_bci + current_length > bci) {

           table[i].length = current_length + delta;

         }

       }

     }

   }

 }

 // Create a new array, copying the src array but adding a hole at

 // the specified location

 static typeArrayOop insert_hole_at(

     size_t where, int hole_sz, typeArrayOop src) {

   Thread* THREAD = Thread::current();

   Handle src_hnd(THREAD, src);

   typeArrayOop dst =

       oopFactory::new_permanent_byteArray(src->length() + hole_sz, CHECK_NULL);

   src = (typeArrayOop)src_hnd();

   address src_addr = (address)src->byte_at_addr(0);

   address dst_addr = (address)dst->byte_at_addr(0);

   memcpy(dst_addr, src_addr, where);

   memcpy(dst_addr + where + hole_sz,

          src_addr + where, src->length() - where);

   return dst;

 }

 // The width of instruction at "bci" is changing by "delta".  Adjust the stack

 // map frames.

 void Relocator::adjust_stack_map_table(int bci, int delta) {

   if (method()->has_stackmap_table()) {

     typeArrayOop data = method()->stackmap_data();

     // The data in the array is a classfile representation of the stackmap table

     stack_map_table* sm_table =

         stack_map_table::at((address)data->byte_at_addr(0));

     int count = sm_table->number_of_entries();

     stack_map_frame* frame = sm_table->entries();

     int bci_iter = -1;

     bool offset_adjusted = false; // only need to adjust one offset

     for (int i = 0; i < count; ++i) {

       int offset_delta = frame->offset_delta();

       bci_iter += offset_delta;

       if (!offset_adjusted && bci_iter > bci) {

         int new_offset_delta = offset_delta + delta;

         if (frame->is_valid_offset(new_offset_delta)) {

           frame->set_offset_delta(new_offset_delta);

         } else {

           assert(frame->is_same_frame() ||

                  frame->is_same_locals_1_stack_item_frame(),

                  "Frame must be one of the compressed forms");

           // The new delta exceeds the capacity of the 'same_frame' or

           // 'same_frame_1_stack_item_frame' frame types.  We need to

           // convert these frames to the extended versions, but the extended

           // version is bigger and requires more room.  So we allocate a

           // new array and copy the data, being sure to leave u2-sized hole

           // right after the 'frame_type' for the new offset field.

           //

           // We can safely ignore the reverse situation as a small delta

           // can still be used in an extended version of the frame.

           size_t frame_offset = (address)frame - (address)data->byte_at_addr(0);

           data = insert_hole_at(frame_offset + 1, 2, data);

           if (data == NULL) {

             return; // out-of-memory?

           }

           address frame_addr = (address)(data->byte_at_addr(0) + frame_offset);

           frame = stack_map_frame::at(frame_addr);

           // Now convert the frames in place

           if (frame->is_same_frame()) {

             same_frame_extended::create_at(frame_addr, new_offset_delta);

           } else {

             same_locals_1_stack_item_extended::create_at(

               frame_addr, new_offset_delta, NULL);

             // the verification_info_type should already be at the right spot

           }

         }

         offset_adjusted = true; // needs to be done only once, since subsequent

                                 // values are offsets from the current

       }

       // The stack map frame may contain verification types, if so we need to

       // check and update any Uninitialized type's bci (no matter where it is).

       int number_of_types = frame->number_of_types();

       verification_type_info* types = frame->types();

       for (int i = 0; i < number_of_types; ++i) {

         if (types->is_uninitialized() && types->bci() > bci) {

           types->set_bci(types->bci() + delta);

         }

         types = types->next();

       }

       // Full frame has stack values too

       full_frame* ff = frame->as_full_frame();

       if (ff != NULL) {

         address eol = (address)types;

         number_of_types = ff->stack_slots(eol);

         types = ff->stack(eol);

         for (int i = 0; i < number_of_types; ++i) {

           if (types->is_uninitialized() && types->bci() > bci) {

             types->set_bci(types->bci() + delta);

           }

           types = types->next();

         }

       }

       frame = frame->next();

     }

     method()->set_stackmap_data(data); // in case it has changed

   }

 }

 bool Relocator::expand_code_array(int delta) {

   int length = MAX2(code_length() + delta, code_length() * (100+code_slop_pct()) / 100);

   if (length > MAX_METHOD_LENGTH) {

     if (delta == 0 && code_length() <= MAX_METHOD_LENGTH) {

       length = MAX_METHOD_LENGTH;

     } else {

       return false;

     }

   }

   unsigned char* new_code_array = NEW_RESOURCE_ARRAY(unsigned char, length);

   if (!new_code_array) return false;

   // Expanding current array

   if (code_array() != NULL) {

     memcpy(new_code_array, code_array(), code_length());

   } else {

     // Initial copy. Copy directly from methodOop

     memcpy(new_code_array, method()->code_base(), code_length());

   }

   set_code_array(new_code_array);

   set_code_array_length(length);

   return true;

 }

 // The instruction at "bci", whose size is "ilen", is changing size by

 // "delta".  Reallocate, move code, recalculate jumps, and enqueue

 // change items as necessary.

 bool Relocator::relocate_code(int bci, int ilen, int delta) {

   int next_bci = bci + ilen;

   if (delta > 0 && code_length() + delta > code_array_length())  {

     // Expand allocated code space, if necessary.

     if (!expand_code_array(delta)) {

           return false;

     }

   }

   // We require 4-byte alignment of code arrays.

   assert(((intptr_t)code_array() & 3) == 0, "check code alignment");

   // Change jumps before doing the copying; this routine requires aligned switches.

   change_jumps(bci, delta);

   // In case we have shrunken a tableswitch/lookupswitch statement, we store the last

   // bytes that get overwritten. We have to copy the bytes after the change_jumps method

   // has been called, since it is likly to update last offset in a tableswitch/lookupswitch

   if (delta < 0) {

     assert(delta>=-3, "we cannot overwrite more than 3 bytes");

     memcpy(_overwrite, addr_at(bci + ilen + delta), -delta);

   }

   memmove(addr_at(next_bci + delta), addr_at(next_bci), code_length() - next_bci);

   set_code_length(code_length() + delta);

   // Also adjust exception tables...

   adjust_exception_table(bci, delta);

   // Line number tables...

   adjust_line_no_table(bci, delta);

   // And local variable table...

   adjust_local_var_table(bci, delta);

   // Adjust stack maps

   adjust_stack_map_table(bci, delta);

   // Relocate the pending change stack...

   for (int j = 0; j < _changes->length(); j++) {

     ChangeItem* ci = _changes->at(j);

     ci->relocate(bci, delta);

   }

   // Notify any listeners about code relocation

   notify(bci, delta, code_length());

   return true;

 }

 // relocate a general instruction. Called by ChangeWiden class

 bool Relocator::handle_widen(int bci, int new_ilen, u_char inst_buffer[]) {

   int ilen = rc_instr_len(bci);

   if (!relocate_code(bci, ilen, new_ilen - ilen))

     return false;

   // Insert new bytecode(s)

   for(int k = 0; k < new_ilen; k++) {

     code_at_put(bci + k, (Bytecodes::Code)inst_buffer[k]);

   }

   return true;

 }

 // handle jump_widen instruction. Called be ChangeJumpWiden class

 bool Relocator::handle_jump_widen(int bci, int delta) {

   int ilen = rc_instr_len(bci);

   Bytecodes::Code bc = code_at(bci);

   switch (bc) {

     case Bytecodes::_ifeq:

     case Bytecodes::_ifne:

     case Bytecodes::_iflt:

     case Bytecodes::_ifge:

     case Bytecodes::_ifgt:

     case Bytecodes::_ifle:

     case Bytecodes::_if_icmpeq:

     case Bytecodes::_if_icmpne:

     case Bytecodes::_if_icmplt:

     case Bytecodes::_if_icmpge:

     case Bytecodes::_if_icmpgt:

     case Bytecodes::_if_icmple:

     case Bytecodes::_if_acmpeq:

     case Bytecodes::_if_acmpne:

     case Bytecodes::_ifnull:

     case Bytecodes::_ifnonnull: {

       const int goto_length   = Bytecodes::length_for(Bytecodes::_goto);

       // If 'if' points to the next bytecode after goto, it's already handled.

       // it shouldn't be.

       assert (short_at(bci+1) != ilen+goto_length, "if relocation already handled");

       assert(ilen == 3, "check length");

       // Convert to 0 if <cond> goto 6

       //            3 _goto 11

       //            6 _goto_w <wide delta offset>

       //            11 <else code>

       const int goto_w_length = Bytecodes::length_for(Bytecodes::_goto_w);

       const int add_bci = goto_length + goto_w_length;

       if (!relocate_code(bci, 3, /*delta*/add_bci)) return false;

       // if bytecode points to goto_w instruction

       short_at_put(bci + 1, ilen + goto_length);

       int cbci = bci + ilen;

       // goto around

       code_at_put(cbci, Bytecodes::_goto);

       short_at_put(cbci + 1, add_bci);

       // goto_w <wide delta>

       cbci = cbci + goto_length;

       code_at_put(cbci, Bytecodes::_goto_w);

       if (delta > 0) {

         delta += 2;                 // goto_w is 2 bytes more than "if" code

       } else {

         delta -= ilen+goto_length;  // branch starts at goto_w offset

       }

       int_at_put(cbci + 1, delta);

       break;

       }

     case Bytecodes::_goto:

     case Bytecodes::_jsr:

       assert(ilen == 3, "check length");

       if (!relocate_code(bci, 3, 2)) return false;

       if (bc == Bytecodes::_goto)

         code_at_put(bci, Bytecodes::_goto_w);

       else

         code_at_put(bci, Bytecodes::_jsr_w);

       // If it's a forward jump, add 2 for the widening.

       if (delta > 0) delta += 2;

       int_at_put(bci + 1, delta);

       break;

     default: ShouldNotReachHere();

   }

   return true;

 }

 // handle lookup/table switch instructions.  Called be ChangeSwitchPad class

 bool Relocator::handle_switch_pad(int bci, int old_pad, bool is_lookup_switch) {

   int ilen = rc_instr_len(bci);

   int new_pad = align(bci+1) - (bci+1);

   int pad_delta = new_pad - old_pad;

   if (pad_delta != 0) {

     int len;

     if (!is_lookup_switch) {

       int low  = int_at(bci+1+old_pad+4);

       int high = int_at(bci+1+old_pad+8);

       len = high-low+1 + 3; // 3 for default, hi, lo.

     } else {

       int npairs = int_at(bci+1+old_pad+4);

       len = npairs*2 + 2; // 2 for default, npairs.

     }

     // Because "relocateCode" does a "changeJumps" loop,

     // which parses instructions to determine their length,

     // we need to call that before messing with the current

     // instruction.  Since it may also overwrite the current

     // instruction when moving down, remember the possibly

     // overwritten part.

     // Move the code following the instruction...

     if (!relocate_code(bci, ilen, pad_delta)) return false;

     if (pad_delta < 0) {

       // Move the shrunken instruction down.

       memmove(addr_at(bci + 1 + new_pad),

               addr_at(bci + 1 + old_pad),

               len * 4 + pad_delta);

       memmove(addr_at(bci + 1 + new_pad + len*4 + pad_delta),

               _overwrite, -pad_delta);

     } else {

       assert(pad_delta > 0, "check");

       // Move the expanded instruction up.

       memmove(addr_at(bci +1 + new_pad),

               addr_at(bci +1 + old_pad),

               len * 4);

       memset(addr_at(bci + 1), 0, new_pad); // pad must be 0

     }

   }

   return true;

 }