1 /*
   2  * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/stackMapTableFormat.hpp"
  27 #include "interpreter/bytecodes.hpp"
  28 #include "memory/metadataFactory.hpp"
  29 #include "memory/oopFactory.hpp"
  30 #include "memory/universe.inline.hpp"
  31 #include "oops/oop.inline.hpp"
  32 #include "runtime/handles.inline.hpp"
  33 #include "runtime/relocator.hpp"
  34 
  35 #define MAX_METHOD_LENGTH  65535
  36 
  37 #define MAX_SHORT ((1 << 15) - 1)
  38 #define MIN_SHORT (- (1 << 15))
  39 
  40 // Encapsulates a code change request. There are 3 types.
  41 // General instruction, jump instruction, and table/lookup switches
  42 //
  43 class ChangeItem : public ResourceObj {
  44   int _bci;
  45  public:
  46    ChangeItem(int bci) { _bci = bci; }
  47    virtual bool handle_code_change(Relocator *r) = 0;
  48 
  49    // type info
  50    virtual bool is_widen()      { return false; }
  51    virtual bool is_jump_widen() { return false; }
  52    virtual bool is_switch_pad() { return false; }
  53 
  54    // accessors
  55    int bci()    { return _bci; }
  56    void relocate(int break_bci, int delta) { if (_bci > break_bci) { _bci += delta; } }
  57 
  58    virtual bool adjust(int bci, int delta) { return false; }
  59 
  60    // debug
  61    virtual void print() = 0;
  62 };
  63 
  64 class ChangeWiden : public ChangeItem {
  65   int              _new_ilen;    // New length of instruction at bci
  66   u_char*          _inst_buffer; // New bytecodes
  67  public:
  68   ChangeWiden(int bci, int new_ilen, u_char* inst_buffer) : ChangeItem(bci) {
  69     _new_ilen = new_ilen;
  70     _inst_buffer = inst_buffer;
  71   }
  72 
  73   // Callback to do instruction
  74   bool handle_code_change(Relocator *r) { return r->handle_widen(bci(), _new_ilen, _inst_buffer); };
  75 
  76   bool is_widen()              { return true; }
  77 
  78   void print()                 { tty->print_cr("ChangeWiden. bci: %d   New_ilen: %d", bci(), _new_ilen); }
  79 };
  80 
  81 class ChangeJumpWiden : public ChangeItem {
  82   int _delta;  // New length of instruction at bci
  83  public:
  84   ChangeJumpWiden(int bci, int delta) : ChangeItem(bci) { _delta = delta; }
  85 
  86   // Callback to do instruction
  87   bool handle_code_change(Relocator *r) { return r->handle_jump_widen(bci(), _delta); };
  88 
  89   bool is_jump_widen()         { return true; }
  90 
  91   // If the bci matches, adjust the delta in the change jump request.
  92   bool adjust(int jump_bci, int delta) {
  93     if (bci() == jump_bci) {
  94       if (_delta > 0)
  95         _delta += delta;
  96       else
  97         _delta -= delta;
  98       return true;
  99     }
 100     return false;
 101   }
 102 
 103   void print()                 { tty->print_cr("ChangeJumpWiden. bci: %d   Delta: %d", bci(), _delta); }
 104 };
 105 
 106 class ChangeSwitchPad : public ChangeItem {
 107   int  _padding;
 108   bool _is_lookup_switch;
 109  public:
 110    ChangeSwitchPad(int bci, int padding, bool is_lookup_switch) : ChangeItem(bci) {
 111      _padding = padding;
 112      _is_lookup_switch = is_lookup_switch;
 113    }
 114 
 115    // Callback to do instruction
 116    bool handle_code_change(Relocator *r) { return r->handle_switch_pad(bci(), _padding, _is_lookup_switch); };
 117 
 118    bool is_switch_pad()        { return true; }
 119    int  padding()              { return _padding;  }
 120    bool is_lookup_switch()     { return _is_lookup_switch; }
 121 
 122    void print()                { tty->print_cr("ChangeSwitchPad. bci: %d   Padding: %d  IsLookupSwitch: %d", bci(), _padding, _is_lookup_switch); }
 123 };
 124 
 125 //-----------------------------------------------------------------------------------------------------------
 126 // Relocator code
 127 
 128 Relocator::Relocator(const methodHandle& m, RelocatorListener* listener) {
 129   set_method(m);
 130   set_code_length(method()->code_size());
 131   set_code_array(NULL);
 132   // Allocate code array and copy bytecodes
 133   if (!expand_code_array(0)) {
 134     // Should have at least MAX_METHOD_LENGTH available or the verifier
 135     // would have failed.
 136     ShouldNotReachHere();
 137   }
 138   set_compressed_line_number_table(NULL);
 139   set_compressed_line_number_table_size(0);
 140   _listener = listener;
 141 }
 142 
 143 // size is the new size of the instruction at bci. Hence, if size is less than the current
 144 // instruction size, we will shrink the code.
 145 methodHandle Relocator::insert_space_at(int bci, int size, u_char inst_buffer[], TRAPS) {
 146   _changes = new GrowableArray<ChangeItem*> (10);
 147   _changes->push(new ChangeWiden(bci, size, inst_buffer));
 148 
 149   if (TraceRelocator) {
 150     tty->print_cr("Space at: %d Size: %d", bci, size);
 151     _method->print();
 152     _method->print_codes();
 153     tty->print_cr("-------------------------------------------------");
 154   }
 155 
 156   if (!handle_code_changes()) return methodHandle();
 157 
 158     // Construct the new method
 159   methodHandle new_method = Method::clone_with_new_data(method(),
 160                               code_array(), code_length(),
 161                               compressed_line_number_table(),
 162                               compressed_line_number_table_size(),
 163                               CHECK_(methodHandle()));
 164 
 165   // Deallocate the old Method* from metadata
 166   ClassLoaderData* loader_data = method()->method_holder()->class_loader_data();
 167   loader_data->add_to_deallocate_list(method()());
 168 
 169     set_method(new_method);
 170 
 171   if (TraceRelocator) {
 172     tty->print_cr("-------------------------------------------------");
 173     tty->print_cr("new method");
 174     _method->print_codes();
 175   }
 176 
 177   return new_method;
 178 }
 179 
 180 
 181 bool Relocator::handle_code_changes() {
 182   assert(_changes != NULL, "changes vector must be initialized");
 183 
 184   while (!_changes->is_empty()) {
 185     // Inv: everything is aligned.
 186     ChangeItem* ci = _changes->first();
 187 
 188     if (TraceRelocator) {
 189       ci->print();
 190     }
 191 
 192     // Execute operation
 193     if (!ci->handle_code_change(this)) return false;
 194 
 195     // Shuffle items up
 196     for (int index = 1; index < _changes->length(); index++) {
 197       _changes->at_put(index-1, _changes->at(index));
 198     }
 199     _changes->pop();
 200   }
 201   return true;
 202 }
 203 
 204 
 205 bool Relocator::is_opcode_lookupswitch(Bytecodes::Code bc) {
 206   switch (bc) {
 207     case Bytecodes::_tableswitch:       return false;
 208     case Bytecodes::_lookupswitch:                   // not rewritten on ia64
 209     case Bytecodes::_fast_linearswitch:              // rewritten _lookupswitch
 210     case Bytecodes::_fast_binaryswitch: return true; // rewritten _lookupswitch
 211     default: ShouldNotReachHere();
 212   }
 213   return true; // dummy
 214 }
 215 
 216 // We need a special instruction size method, since lookupswitches and tableswitches might not be
 217 // properly aligned during relocation
 218 int Relocator::rc_instr_len(int bci) {
 219   Bytecodes::Code bc= code_at(bci);
 220   switch (bc) {
 221     // In the case of switch instructions, see if we have the original
 222     // padding recorded.
 223     case Bytecodes::_tableswitch:
 224     case Bytecodes::_lookupswitch:
 225     case Bytecodes::_fast_linearswitch:
 226     case Bytecodes::_fast_binaryswitch:
 227     {
 228       int pad = get_orig_switch_pad(bci, is_opcode_lookupswitch(bc));
 229       if (pad == -1) {
 230         return instruction_length_at(bci);
 231       }
 232       // Otherwise, depends on the switch type.
 233       switch (bc) {
 234         case Bytecodes::_tableswitch: {
 235           int lo = int_at(bci + 1 + pad + 4 * 1);
 236           int hi = int_at(bci + 1 + pad + 4 * 2);
 237           int n = hi - lo + 1;
 238           return 1 + pad + 4*(3 + n);
 239         }
 240         case Bytecodes::_lookupswitch:
 241         case Bytecodes::_fast_linearswitch:
 242         case Bytecodes::_fast_binaryswitch: {
 243           int npairs = int_at(bci + 1 + pad + 4 * 1);
 244           return 1 + pad + 4*(2 + 2*npairs);
 245         }
 246         default:
 247           ShouldNotReachHere();
 248       }
 249     }
 250   }
 251   return instruction_length_at(bci);
 252 }
 253 
 254 // If a change item is recorded for "pc", with type "ct", returns the
 255 // associated padding, else -1.
 256 int Relocator::get_orig_switch_pad(int bci, bool is_lookup_switch) {
 257   for (int k = 0; k < _changes->length(); k++) {
 258     ChangeItem* ci = _changes->at(k);
 259     if (ci->is_switch_pad()) {
 260       ChangeSwitchPad* csp = (ChangeSwitchPad*)ci;
 261       if (csp->is_lookup_switch() == is_lookup_switch && csp->bci() == bci) {
 262         return csp->padding();
 263       }
 264     }
 265   }
 266   return -1;
 267 }
 268 
 269 
 270 // Push a ChangeJumpWiden if it doesn't already exist on the work queue,
 271 // otherwise adjust the item already there by delta.  The calculation for
 272 // new_delta is wrong for this because it uses the offset stored in the
 273 // code stream itself which wasn't fixed when item was pushed on the work queue.
 274 void Relocator::push_jump_widen(int bci, int delta, int new_delta) {
 275   for (int j = 0; j < _changes->length(); j++) {
 276     ChangeItem* ci = _changes->at(j);
 277     if (ci->adjust(bci, delta)) return;
 278   }
 279   _changes->push(new ChangeJumpWiden(bci, new_delta));
 280 }
 281 
 282 
 283 // The current instruction of "c" is a jump; one of its offset starts
 284 // at "offset" and is a short if "isShort" is "TRUE",
 285 // and an integer otherwise.  If the jump crosses "breakPC", change
 286 // the span of the jump by "delta".
 287 void Relocator::change_jump(int bci, int offset, bool is_short, int break_bci, int delta) {
 288   int bci_delta = (is_short) ? short_at(offset) : int_at(offset);
 289   int targ = bci + bci_delta;
 290 
 291   if ((bci <= break_bci && targ >  break_bci) ||
 292       (bci >  break_bci && targ <= break_bci)) {
 293     int new_delta;
 294     if (bci_delta > 0)
 295       new_delta = bci_delta + delta;
 296     else
 297       new_delta = bci_delta - delta;
 298 
 299     if (is_short && ((new_delta > MAX_SHORT) || new_delta < MIN_SHORT)) {
 300       push_jump_widen(bci, delta, new_delta);
 301     } else if (is_short) {
 302       short_at_put(offset, new_delta);
 303     } else {
 304       int_at_put(offset, new_delta);
 305     }
 306   }
 307 }
 308 
 309 
 310 // Changes all jumps crossing "break_bci" by "delta".  May enqueue things
 311 // on "rc->changes"
 312 void Relocator::change_jumps(int break_bci, int delta) {
 313   int bci = 0;
 314   Bytecodes::Code bc;
 315   // Now, adjust any affected instructions.
 316   while (bci < code_length()) {
 317     switch (bc= code_at(bci)) {
 318       case Bytecodes::_ifeq:
 319       case Bytecodes::_ifne:
 320       case Bytecodes::_iflt:
 321       case Bytecodes::_ifge:
 322       case Bytecodes::_ifgt:
 323       case Bytecodes::_ifle:
 324       case Bytecodes::_if_icmpeq:
 325       case Bytecodes::_if_icmpne:
 326       case Bytecodes::_if_icmplt:
 327       case Bytecodes::_if_icmpge:
 328       case Bytecodes::_if_icmpgt:
 329       case Bytecodes::_if_icmple:
 330       case Bytecodes::_if_acmpeq:
 331       case Bytecodes::_if_acmpne:
 332       case Bytecodes::_ifnull:
 333       case Bytecodes::_ifnonnull:
 334       case Bytecodes::_goto:
 335       case Bytecodes::_jsr:
 336         change_jump(bci, bci+1, true, break_bci, delta);
 337         break;
 338       case Bytecodes::_goto_w:
 339       case Bytecodes::_jsr_w:
 340         change_jump(bci, bci+1, false, break_bci, delta);
 341         break;
 342       case Bytecodes::_tableswitch:
 343       case Bytecodes::_lookupswitch:
 344       case Bytecodes::_fast_linearswitch:
 345       case Bytecodes::_fast_binaryswitch: {
 346         int recPad = get_orig_switch_pad(bci, (bc != Bytecodes::_tableswitch));
 347         int oldPad = (recPad != -1) ? recPad : align(bci+1) - (bci+1);
 348         if (bci > break_bci) {
 349           int new_bci = bci + delta;
 350           int newPad = align(new_bci+1) - (new_bci+1);
 351           // Do we need to check the padding?
 352           if (newPad != oldPad) {
 353             if (recPad == -1) {
 354               _changes->push(new ChangeSwitchPad(bci, oldPad, (bc != Bytecodes::_tableswitch)));
 355             }
 356           }
 357         }
 358 
 359         // Then the rest, which depend on the kind of switch.
 360         switch (bc) {
 361           case Bytecodes::_tableswitch: {
 362             change_jump(bci, bci +1 + oldPad, false, break_bci, delta);
 363             // We cannot use the Bytecode_tableswitch abstraction, since the padding might not be correct.
 364             int lo = int_at(bci + 1 + oldPad + 4 * 1);
 365             int hi = int_at(bci + 1 + oldPad + 4 * 2);
 366             int n = hi - lo + 1;
 367             for (int k = 0; k < n; k++) {
 368               change_jump(bci, bci +1 + oldPad + 4*(k+3), false, break_bci, delta);
 369             }
 370             // Special next-bci calculation here...
 371             bci += 1 + oldPad + (n+3)*4;
 372             continue;
 373           }
 374           case Bytecodes::_lookupswitch:
 375           case Bytecodes::_fast_linearswitch:
 376           case Bytecodes::_fast_binaryswitch: {
 377             change_jump(bci, bci +1 + oldPad, false, break_bci, delta);
 378             // We cannot use the Bytecode_lookupswitch abstraction, since the padding might not be correct.
 379             int npairs = int_at(bci + 1 + oldPad + 4 * 1);
 380             for (int k = 0; k < npairs; k++) {
 381               change_jump(bci, bci + 1 + oldPad + 4*(2 + 2*k + 1), false, break_bci, delta);
 382             }
 383             /* Special next-bci calculation here... */
 384             bci += 1 + oldPad + (2 + (npairs*2))*4;
 385             continue;
 386           }
 387           default:
 388             ShouldNotReachHere();
 389         }
 390       }
 391       default:
 392         break;
 393     }
 394     bci += rc_instr_len(bci);
 395   }
 396 }
 397 
 398 // The width of instruction at "pc" is changing by "delta".  Adjust the
 399 // exception table, if any, of "rc->mb".
 400 void Relocator::adjust_exception_table(int bci, int delta) {
 401   ExceptionTable table(_method());
 402   for (int index = 0; index < table.length(); index ++) {
 403     if (table.start_pc(index) > bci) {
 404       table.set_start_pc(index, table.start_pc(index) + delta);
 405       table.set_end_pc(index, table.end_pc(index) + delta);
 406     } else if (bci < table.end_pc(index)) {
 407       table.set_end_pc(index, table.end_pc(index) + delta);
 408     }
 409     if (table.handler_pc(index) > bci)
 410       table.set_handler_pc(index, table.handler_pc(index) + delta);
 411   }
 412 }
 413 
 414 
 415 // The width of instruction at "bci" is changing by "delta".  Adjust the line number table.
 416 void Relocator::adjust_line_no_table(int bci, int delta) {
 417   if (method()->has_linenumber_table()) {
 418     CompressedLineNumberReadStream  reader(method()->compressed_linenumber_table());
 419     CompressedLineNumberWriteStream writer(64);  // plenty big for most line number tables
 420     while (reader.read_pair()) {
 421       int adjustment = (reader.bci() > bci) ? delta : 0;
 422       writer.write_pair(reader.bci() + adjustment, reader.line());
 423     }
 424     writer.write_terminator();
 425     set_compressed_line_number_table(writer.buffer());
 426     set_compressed_line_number_table_size(writer.position());
 427   }
 428 }
 429 
 430 
 431 // The width of instruction at "bci" is changing by "delta".  Adjust the local variable table.
 432 void Relocator::adjust_local_var_table(int bci, int delta) {
 433   int localvariable_table_length = method()->localvariable_table_length();
 434   if (localvariable_table_length > 0) {
 435     LocalVariableTableElement* table = method()->localvariable_table_start();
 436     for (int i = 0; i < localvariable_table_length; i++) {
 437       u2 current_bci = table[i].start_bci;
 438       if (current_bci > bci) {
 439         table[i].start_bci = current_bci + delta;
 440       } else {
 441         u2 current_length = table[i].length;
 442         if (current_bci + current_length > bci) {
 443           table[i].length = current_length + delta;
 444         }
 445       }
 446     }
 447   }
 448 }
 449 
 450 // Create a new array, copying the src array but adding a hole at
 451 // the specified location
 452 static Array<u1>* insert_hole_at(ClassLoaderData* loader_data,
 453     size_t where, int hole_sz, Array<u1>* src) {
 454   Thread* THREAD = Thread::current();
 455   Array<u1>* dst =
 456       MetadataFactory::new_array<u1>(loader_data, src->length() + hole_sz, 0, CHECK_NULL);
 457 
 458   address src_addr = (address)src->adr_at(0);
 459   address dst_addr = (address)dst->adr_at(0);
 460 
 461   memcpy(dst_addr, src_addr, where);
 462   memcpy(dst_addr + where + hole_sz,
 463          src_addr + where, src->length() - where);
 464   return dst;
 465 }
 466 
 467 // The width of instruction at "bci" is changing by "delta".  Adjust the stack
 468 // map frames.
 469 void Relocator::adjust_stack_map_table(int bci, int delta) {
 470   if (method()->has_stackmap_table()) {
 471     Array<u1>* data = method()->stackmap_data();
 472     // The data in the array is a classfile representation of the stackmap table
 473     stack_map_table* sm_table =
 474         stack_map_table::at((address)data->adr_at(0));
 475 
 476     int count = sm_table->number_of_entries();
 477     stack_map_frame* frame = sm_table->entries();
 478     int bci_iter = -1;
 479     bool offset_adjusted = false; // only need to adjust one offset
 480 
 481     for (int i = 0; i < count; ++i) {
 482       int offset_delta = frame->offset_delta();
 483       bci_iter += offset_delta;
 484 
 485       if (!offset_adjusted && bci_iter > bci) {
 486         int new_offset_delta = offset_delta + delta;
 487 
 488         if (frame->is_valid_offset(new_offset_delta)) {
 489           frame->set_offset_delta(new_offset_delta);
 490         } else {
 491           assert(frame->is_same_frame() ||
 492                  frame->is_same_locals_1_stack_item_frame(),
 493                  "Frame must be one of the compressed forms");
 494           // The new delta exceeds the capacity of the 'same_frame' or
 495           // 'same_frame_1_stack_item_frame' frame types.  We need to
 496           // convert these frames to the extended versions, but the extended
 497           // version is bigger and requires more room.  So we allocate a
 498           // new array and copy the data, being sure to leave u2-sized hole
 499           // right after the 'frame_type' for the new offset field.
 500           //
 501           // We can safely ignore the reverse situation as a small delta
 502           // can still be used in an extended version of the frame.
 503 
 504           size_t frame_offset = (address)frame - (address)data->adr_at(0);
 505 
 506           ClassLoaderData* loader_data = method()->method_holder()->class_loader_data();
 507           Array<u1>* new_data = insert_hole_at(loader_data, frame_offset + 1, 2, data);
 508           if (new_data == NULL) {
 509             return; // out-of-memory?
 510           }
 511           // Deallocate old data
 512           MetadataFactory::free_array<u1>(loader_data, data);
 513           data = new_data;
 514 
 515           address frame_addr = (address)(data->adr_at(0) + frame_offset);
 516           frame = stack_map_frame::at(frame_addr);
 517 
 518 
 519           // Now convert the frames in place
 520           if (frame->is_same_frame()) {
 521             same_frame_extended::create_at(frame_addr, new_offset_delta);
 522           } else {
 523             same_locals_1_stack_item_extended::create_at(
 524               frame_addr, new_offset_delta, NULL);
 525             // the verification_info_type should already be at the right spot
 526           }
 527         }
 528         offset_adjusted = true; // needs to be done only once, since subsequent
 529                                 // values are offsets from the current
 530       }
 531 
 532       // The stack map frame may contain verification types, if so we need to
 533       // check and update any Uninitialized type's bci (no matter where it is).
 534       int number_of_types = frame->number_of_types();
 535       verification_type_info* types = frame->types();
 536 
 537       for (int i = 0; i < number_of_types; ++i) {
 538         if (types->is_uninitialized() && types->bci() > bci) {
 539           types->set_bci(types->bci() + delta);
 540         }
 541         types = types->next();
 542       }
 543 
 544       // Full frame has stack values too
 545       full_frame* ff = frame->as_full_frame();
 546       if (ff != NULL) {
 547         address eol = (address)types;
 548         number_of_types = ff->stack_slots(eol);
 549         types = ff->stack(eol);
 550         for (int i = 0; i < number_of_types; ++i) {
 551           if (types->is_uninitialized() && types->bci() > bci) {
 552             types->set_bci(types->bci() + delta);
 553           }
 554           types = types->next();
 555         }
 556       }
 557 
 558       frame = frame->next();
 559     }
 560 
 561     method()->set_stackmap_data(data); // in case it has changed
 562   }
 563 }
 564 
 565 
 566 bool Relocator::expand_code_array(int delta) {
 567   int length = MAX2(code_length() + delta, code_length() * (100+code_slop_pct()) / 100);
 568 
 569   if (length > MAX_METHOD_LENGTH) {
 570     if (delta == 0 && code_length() <= MAX_METHOD_LENGTH) {
 571       length = MAX_METHOD_LENGTH;
 572     } else {
 573       return false;
 574     }
 575   }
 576 
 577   unsigned char* new_code_array = NEW_RESOURCE_ARRAY(unsigned char, length);
 578   if (!new_code_array) return false;
 579 
 580   // Expanding current array
 581   if (code_array() != NULL) {
 582     memcpy(new_code_array, code_array(), code_length());
 583   } else {
 584     // Initial copy. Copy directly from Method*
 585     memcpy(new_code_array, method()->code_base(), code_length());
 586   }
 587 
 588   set_code_array(new_code_array);
 589   set_code_array_length(length);
 590 
 591   return true;
 592 }
 593 
 594 
 595 // The instruction at "bci", whose size is "ilen", is changing size by
 596 // "delta".  Reallocate, move code, recalculate jumps, and enqueue
 597 // change items as necessary.
 598 bool Relocator::relocate_code(int bci, int ilen, int delta) {
 599   int next_bci = bci + ilen;
 600   if (delta > 0 && code_length() + delta > code_array_length())  {
 601     // Expand allocated code space, if necessary.
 602     if (!expand_code_array(delta)) {
 603           return false;
 604     }
 605   }
 606 
 607   // We require 4-byte alignment of code arrays.
 608   assert(((intptr_t)code_array() & 3) == 0, "check code alignment");
 609   // Change jumps before doing the copying; this routine requires aligned switches.
 610   change_jumps(bci, delta);
 611 
 612   // In case we have shrunken a tableswitch/lookupswitch statement, we store the last
 613   // bytes that get overwritten. We have to copy the bytes after the change_jumps method
 614   // has been called, since it is likely to update last offset in a tableswitch/lookupswitch
 615   if (delta < 0) {
 616     assert(delta>=-3, "we cannot overwrite more than 3 bytes");
 617     memcpy(_overwrite, addr_at(bci + ilen + delta), -delta);
 618   }
 619 
 620   memmove(addr_at(next_bci + delta), addr_at(next_bci), code_length() - next_bci);
 621   set_code_length(code_length() + delta);
 622   // Also adjust exception tables...
 623   adjust_exception_table(bci, delta);
 624   // Line number tables...
 625   adjust_line_no_table(bci, delta);
 626   // And local variable table...
 627   adjust_local_var_table(bci, delta);
 628 
 629   // Adjust stack maps
 630   adjust_stack_map_table(bci, delta);
 631 
 632   // Relocate the pending change stack...
 633   for (int j = 0; j < _changes->length(); j++) {
 634     ChangeItem* ci = _changes->at(j);
 635     ci->relocate(bci, delta);
 636   }
 637 
 638   // Notify any listeners about code relocation
 639   notify(bci, delta, code_length());
 640 
 641   return true;
 642 }
 643 
 644 // relocate a general instruction. Called by ChangeWiden class
 645 bool Relocator::handle_widen(int bci, int new_ilen, u_char inst_buffer[]) {
 646   int ilen = rc_instr_len(bci);
 647   if (!relocate_code(bci, ilen, new_ilen - ilen))
 648     return false;
 649 
 650   // Insert new bytecode(s)
 651   for(int k = 0; k < new_ilen; k++) {
 652     code_at_put(bci + k, (Bytecodes::Code)inst_buffer[k]);
 653   }
 654 
 655   return true;
 656 }
 657 
 658 // handle jump_widen instruction. Called be ChangeJumpWiden class
 659 bool Relocator::handle_jump_widen(int bci, int delta) {
 660   int ilen = rc_instr_len(bci);
 661 
 662   Bytecodes::Code bc = code_at(bci);
 663   switch (bc) {
 664     case Bytecodes::_ifeq:
 665     case Bytecodes::_ifne:
 666     case Bytecodes::_iflt:
 667     case Bytecodes::_ifge:
 668     case Bytecodes::_ifgt:
 669     case Bytecodes::_ifle:
 670     case Bytecodes::_if_icmpeq:
 671     case Bytecodes::_if_icmpne:
 672     case Bytecodes::_if_icmplt:
 673     case Bytecodes::_if_icmpge:
 674     case Bytecodes::_if_icmpgt:
 675     case Bytecodes::_if_icmple:
 676     case Bytecodes::_if_acmpeq:
 677     case Bytecodes::_if_acmpne:
 678     case Bytecodes::_ifnull:
 679     case Bytecodes::_ifnonnull: {
 680       const int goto_length   = Bytecodes::length_for(Bytecodes::_goto);
 681 
 682       // If 'if' points to the next bytecode after goto, it's already handled.
 683       // it shouldn't be.
 684       assert (short_at(bci+1) != ilen+goto_length, "if relocation already handled");
 685       assert(ilen == 3, "check length");
 686 
 687       // Convert to 0 if <cond> goto 6
 688       //            3 _goto 11
 689       //            6 _goto_w <wide delta offset>
 690       //            11 <else code>
 691       const int goto_w_length = Bytecodes::length_for(Bytecodes::_goto_w);
 692       const int add_bci = goto_length + goto_w_length;
 693 
 694       if (!relocate_code(bci, 3, /*delta*/add_bci)) return false;
 695 
 696       // if bytecode points to goto_w instruction
 697       short_at_put(bci + 1, ilen + goto_length);
 698 
 699       int cbci = bci + ilen;
 700       // goto around
 701       code_at_put(cbci, Bytecodes::_goto);
 702       short_at_put(cbci + 1, add_bci);
 703       // goto_w <wide delta>
 704       cbci = cbci + goto_length;
 705       code_at_put(cbci, Bytecodes::_goto_w);
 706       if (delta > 0) {
 707         delta += 2;                 // goto_w is 2 bytes more than "if" code
 708       } else {
 709         delta -= ilen+goto_length;  // branch starts at goto_w offset
 710       }
 711       int_at_put(cbci + 1, delta);
 712       break;
 713 
 714       }
 715     case Bytecodes::_goto:
 716     case Bytecodes::_jsr:
 717       assert(ilen == 3, "check length");
 718 
 719       if (!relocate_code(bci, 3, 2)) return false;
 720       if (bc == Bytecodes::_goto)
 721         code_at_put(bci, Bytecodes::_goto_w);
 722       else
 723         code_at_put(bci, Bytecodes::_jsr_w);
 724 
 725       // If it's a forward jump, add 2 for the widening.
 726       if (delta > 0) delta += 2;
 727       int_at_put(bci + 1, delta);
 728       break;
 729 
 730     default: ShouldNotReachHere();
 731   }
 732 
 733   return true;
 734 }
 735 
 736 // handle lookup/table switch instructions.  Called be ChangeSwitchPad class
 737 bool Relocator::handle_switch_pad(int bci, int old_pad, bool is_lookup_switch) {
 738   int ilen = rc_instr_len(bci);
 739   int new_pad = align(bci+1) - (bci+1);
 740   int pad_delta = new_pad - old_pad;
 741   if (pad_delta != 0) {
 742     int len;
 743     if (!is_lookup_switch) {
 744       int low  = int_at(bci+1+old_pad+4);
 745       int high = int_at(bci+1+old_pad+8);
 746       len = high-low+1 + 3; // 3 for default, hi, lo.
 747     } else {
 748       int npairs = int_at(bci+1+old_pad+4);
 749       len = npairs*2 + 2; // 2 for default, npairs.
 750     }
 751     // Because "relocateCode" does a "changeJumps" loop,
 752     // which parses instructions to determine their length,
 753     // we need to call that before messing with the current
 754     // instruction.  Since it may also overwrite the current
 755     // instruction when moving down, remember the possibly
 756     // overwritten part.
 757 
 758     // Move the code following the instruction...
 759     if (!relocate_code(bci, ilen, pad_delta)) return false;
 760 
 761     if (pad_delta < 0) {
 762       // Move the shrunken instruction down.
 763       memmove(addr_at(bci + 1 + new_pad),
 764               addr_at(bci + 1 + old_pad),
 765               len * 4 + pad_delta);
 766       memmove(addr_at(bci + 1 + new_pad + len*4 + pad_delta),
 767               _overwrite, -pad_delta);
 768     } else {
 769       assert(pad_delta > 0, "check");
 770       // Move the expanded instruction up.
 771       memmove(addr_at(bci +1 + new_pad),
 772               addr_at(bci +1 + old_pad),
 773               len * 4);
 774       memset(addr_at(bci + 1), 0, new_pad); // pad must be 0
 775     }
 776   }
 777   return true;
 778 }