dalvik-constraints.html revision de75089fb7216d19e9c22cce4dc62a49513477d3
1<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 2 3<html> 4 <head> 5 <title>Dalvik bytecode constraints</title> 6 <link rel=stylesheet href="dalvik-constraints.css"> 7 </head> 8 9 <body> 10 11 <h1>Dalvik bytecode constraints</h1> 12 13<!-- 14 <h1>General integrity constraints</h1> 15 16 <table> 17 <tr> 18 <th> 19 Identifier 20 </th> 21 22 <th> 23 Description 24 </th> 25 </tr> 26 27 <tr> 28 <td> 29 A1 30 </td> 31 32 <td> 33 The magic number of the DEX file must be "dex\n035\0". 34 </td> 35 </tr> 36 37 <tr> 38 <td> 39 A1 40 </td> 41 42 <td> 43 The checksum must be an Adler-32 checksum of the whole file contents 44 except magic and checksum field. 45 </td> 46 </tr> 47 48 49The signature must be a SHA-1 hash of the whole file contents except magic, 50checksum, and signature. 51 52The file_size must match the actual file size in bytes. 53 54The header_size must have the value 0x70. 55 56The endian_tag must have either the value ENDIAN_CONSTANT or 57REVERSE_ENDIAN_CONSTANT. 58 59For each of the link, string_ids, type_ids, proto_ids, field_ids, method_ids, class_defs 60and data sections, the offset and size fields must be either both zero or both 61non-zero. In the latter case, the offset must be four-byte-aligned. 62 63All offset fields in the header except map_off must be four-byte-aligned. 64 65The map_off field must be either zero or point into the data section. In the 66latter case, the data section must exist. 67 68None of the link, string_ids, type_ids, proto_ids, field_ids, method_ids, class_defs 69and data sections must overlap each other or the header. 70 71If a map exists, then each map entry must have a valid type. Each type may 72appear at most once. 73 74If a map exists, then each map entry must have a nonzero offset and size. The 75offset must point into the corresponding section of the file (i.e. a 76string_id_item must point into the string_ids section) and the explicit or 77implicit size of the item must match the actual contents and size of the 78section. 79 80If a map exists, then the offset of map entry n+1 must be greater or equal to 81the offset of map entry n plus then size of map entry n. This implies 82non-overlapping entries and low-to-high ordering. 83 84The following types of entries must have an offset that is 85four-byte-aligned: string_id_item, type_id_item, proto_id_item, field_id_item, 86method_id_item, class_def_item, type_list, code_item, 87annotations_directory_item. 88 89For each string_id_item, the string_data_off field must contain a valid 90reference into the data section. For the referenced string_data_item, the data 91field must contain a valid MUTF-8 string, and the utf16_size must match the 92decoded length of the string. 93 94For each type_id_item, the desciptor_idx field must contain a valid reference 95into the string_ids list. The referenced string must be a valid type descriptor. 96 97For each proto_id_item, the shorty_idx field must contain a valid reference 98into the string_ids list. The referenced string must be a valid shorty descriptor. 99Also, the return_type_idx field must be a valid index into the type_ids section, 100and the parameters_off field must be either zero or a valid offset pointing 101into the data section. If nonzero, the parameter list must not contain any void 102entries. 103 104For each field_id_item, both the class_idx and type_idx fields must be a valid 105 indices into the 106type_ids list. The entry referenced by class_idx must be a non-array reference type. 107In addition, the name_idx field must be a valid reference into the string_ids 108section, and the contents of the referenced entry must conform to the MemberName 109specification. 110 111For each method_id_item, the class_idx field must be a valid index into the 112type_ids section, and the 113referenced entry must be a non-array reference type. The proto_id field must 114be a valid reference into the proto_ids list. The name_idx field must be a 115valid reference into the string_ids 116section, and the contents of the referenced entry must conform to the MemberName 117specification. 118 119For each class_def_item, ... 120 121For each field_id_item, the class_idx field must be a valid index into the 122type_ids list. The referenced entry must be a non-array reference type. 123 124... 125 126--> 127 128 <h2> 129 Static constraints 130 </h2> 131 132 <p> 133 Static constraints are constraints on individual elements of the bytecode. 134 They usually can be checked without employing control or data-flow analysis 135 techniques. 136 </p> 137 138 <table> 139 <tr> 140 <th> 141 Identifier 142 </th> 143 144 <th> 145 Description 146 </th> 147 148 <th> 149 Spec equivalent 150 </th> 151 </tr> 152 153 <tr> 154 <td> 155 A1 156 </td> 157 158 <td> 159 The <code>insns</code> array must not be empty. 160 </td> 161 162 <td> 163 4.8.1.1 164 </td> 165 </tr> 166 167 <tr> 168 <td> 169 A2 170 </td> 171 172 <td> 173 The first opcode in the <code>insns</code> array must have index zero. 174 </td> 175 176 <td> 177 4.8.1.3 178 </td> 179 </tr> 180 181 <tr> 182 <td> 183 A3 184 </td> 185 186 <td> 187 The <code>insns</code> array must only contain valid Dalvik opcodes. 188 </td> 189 190 <td> 191 4.8.1.4 192 </td> 193 </tr> 194 195 <tr> 196 <td> 197 A4 198 </td> 199 200 <td> 201 The index of instruction <code>n+1</code> must equal the index of 202 instruction <code>n</code> plus the length of instruction 203 <code>n</code>, taking into account possible operands. 204 </td> 205 206 <td> 207 4.8.1.5 208 </td> 209 </tr> 210 211 <tr> 212 <td> 213 A5 214 </td> 215 216 <td> 217 The last instruction in the <code>insns</code> array must end at index 218 <code>insns_size-1</code>. 219 </td> 220 221 <td> 222 4.8.1.6 223 </td> 224 </tr> 225 226 <tr> 227 <td> 228 A6 229 </td> 230 231 <td> 232 All <code>goto</code> and <code>if-<kind></code> targets must 233 be opcodes within in the same method. 234 </td> 235 236 <td> 237 4.8.1.7 238 </td> 239 </tr> 240 241 <tr> 242 <td> 243 A7 244 </td> 245 246 <td> 247 All targets of a <code>packed-switch</code> instruction must be 248 opcodes within in the same method. The size and the list of targets 249 must be consistent. 250 </td> 251 252 <td> 253 4.8.1.8 254 </td> 255 </tr> 256 257 <tr> 258 <td> 259 A8 260 </td> 261 262 <td> 263 All targets of a <code>sparse-switch</code> instruction must be 264 opcodes within in the same method. The corresponding table must be 265 consistent and sorted low-to-high. 266 </td> 267 268 <td> 269 4.8.1.9 270 </td> 271 </tr> 272 273 <tr> 274 <td> 275 A9 276 </td> 277 278 <td> 279 The <code>B</code> operand of the <code>const-string</code> and 280 <code>const-string/jumbo</code> instructions must be a valid index 281 into the string constant pool. 282 </td> 283 284 <td> 285 4.8.1.10 286 </td> 287 </tr> 288 289 <tr> 290 <td> 291 A10 292 </td> 293 294 <td> 295 The <code>C</code> operand of the <code>iget<kind></code> and 296 <code>iput<kind></code> instructions must be a valid index into 297 the field constant pool. The referenced entry must represent an 298 instance field. 299 </td> 300 301 <td> 302 4.8.1.12 303 </td> 304 </tr> 305 306 <tr> 307 <td> 308 A11 309 </td> 310 311 <td> 312 The <code>C</code> operand of the <code>sget<kind></code> and 313 <code>sput<kind></code> instructions must be a valid index into 314 the field constant pool. The referenced entry must represent a static 315 field. 316 </td> 317 318 <td> 319 4.8.1.12 320 </td> 321 </tr> 322 323 <tr> 324 <td> 325 A12 326 </td> 327 328 <td> 329 The <code>C</code> operand of the <code>invoke-virtual</code>, 330 <code>invoke-super</code>, <code<invoke-direct</code> and 331 <code>invoke-static</code> instructions must be a valid index into the 332 method constant pool. In all cases, the referenced 333 <code>method_id</code> must belong to a class (not an interface). 334 </td> 335 336 <td> 337 4.8.1.13 338 </td> 339 </tr> 340 341 <tr> 342 <td> 343 A13 344 </td> 345 346 <td> 347 The <code>B</code> operand of the <code>invoke-virtual/range</code>, 348 <code>invoke-super/range</code>, <code>invoke-direct/range</code>, and 349 <code>invoke-static/range</code> instructions must be a valid index 350 into the method constant pool. In all cases, the referenced 351 <code>method_id</code> must belong to a class (not an interface). 352 </td> 353 354 <td> 355 4.8.1.13 356 </td> 357 </tr> 358 359 <tr> 360 <td> 361 A14 362 </td> 363 364 <td> 365 A method the name of which starts with a '<' must only be invoked 366 implicitly by the VM, not by code originating from a Dex file. The 367 only exception is the instance initializer, which may be invoked by 368 <code>invoke-direct</code>. 369 </td> 370 371 <td> 372 4.8.1.14 373 </td> 374 </tr> 375 376 <tr> 377 <td> 378 A15 379 </td> 380 381 <td> 382 The <code>C</code> operand of the <code>invoke-interface</code> 383 instruction must be a valid index into the method constant pool. The 384 referenced <code>method_id</code> must belong to an interface (not a 385 class). 386 </td> 387 388 <td> 389 4.8.1.15 390 </td> 391 </tr> 392 393 <tr> 394 <td> 395 A16 396 </td> 397 398 <td> 399 The <code>B</code> operand of the <code>invoke-interface/range</code> 400 instruction must be a valid index into the method constant pool. 401 The referenced <code>method_id</code> must belong to an interface (not 402 a class). 403 </td> 404 405 <td> 406 4.8.1.15 407 </td> 408 </tr> 409 410 <tr> 411 <td> 412 A17 413 </td> 414 415 <td> 416 The <code>B</code> operand of the <code>const-class</code>, 417 <code>check-cast</code>, <code>new-instance</code>, and 418 <code>filled-new-array/range</code> instructions must be a valid index 419 into the type constant pool. 420 </td> 421 422 <td> 423 4.8.1.16 424 </td> 425 </tr> 426 427 <tr> 428 <td> 429 A18 430 </td> 431 432 <td> 433 The <code>C</code> operand of the <code>instance-of</code>, 434 <code>new-array</code>, and <code>filled-new-array</code> 435 instructions must be a valid index into the type constant pool. 436 </td> 437 438 <td> 439 4.8.1.16 440 </td> 441 </tr> 442 443 <tr> 444 <td> 445 A19 446 </td> 447 448 <td> 449 The dimensions of an array created by a <code>new-array</code> 450 instruction must be less than <code>256</code>. 451 </td> 452 453 <td> 454 4.8.1.17 455 </td> 456 </tr> 457 458 <tr> 459 <td> 460 A20 461 </td> 462 463 <td> 464 The <code>new</code> instruction must not refer to array classes, 465 interfaces, or abstract classes. 466 </td> 467 468 <td> 469 4.8.1.18 470 </td> 471 </tr> 472 473 <tr> 474 <td> 475 A21 476 </td> 477 478 <td> 479 The type referred to by a <code>new-array</code> instruction must be 480 a valid, non-reference type. 481 </td> 482 483 <td> 484 4.8.1.20 485 </td> 486 </tr> 487 488 <tr> 489 <td> 490 A22 491 </td> 492 493 <td> 494 All registers referred to by an instruction in a single-width 495 (non-pair) fashion must be valid for the current method. That is, 496 their indices must be non-negative and smaller than 497 <code>registers_size</code>. 498 </td> 499 500 <td> 501 4.8.1.21 502 </td> 503 </tr> 504 505 <tr> 506 <td> 507 A23 508 </td> 509 510 <td> 511 All registers referred to by an instruction in a double-width (pair) 512 fashion must be valid for the current method. That is, their indices 513 must be non-negative and smaller than <code>registers_size-1</code>. 514 </td> 515 516 <td> 517 4.8.1.23 518 </td> 519 </tr> 520 </table> 521 522 <h2> 523 Structural constraints 524 </h2> 525 526 <p> 527 Structural constraints are constraints on relationships between several 528 elements of the bytecode. They usually can't be checked without employing 529 control or data-flow analysis techniques. 530 </p> 531 532 <table> 533 <tr> 534 <th> 535 Identifier 536 </th> 537 538 <th> 539 Description 540 </th> 541 542 <th> 543 Spec equivalent 544 </th> 545 </tr> 546 547 <tr> 548 <td> 549 B1 550 </td> 551 552 <td> 553 The number and types of arguments (registers and immediate values) 554 must always match the instruction. 555 </td> 556 557 <td> 558 4.8.2.1 559 </td> 560 </tr> 561 562 <tr> 563 <td> 564 B2 565 </td> 566 567 <td> 568 Register pairs must never be broken up. 569 </td> 570 571 <td> 572 4.8.2.3 573 </td> 574 </tr> 575 576 <tr> 577 <td> 578 B3 579 </td> 580 581 <td> 582 A register (or pair) has to be assigned first before it can be 583 read. 584 </td> 585 586 <td> 587 4.8.2.4 588 </td> 589 </tr> 590 591 <tr> 592 <td> 593 B4 594 </td> 595 596 <td> 597 An <code>invoke-direct</code> instruction must only invoke an instance 598 initializer or a method in the current class or one of its 599 superclasses. 600 </td> 601 602 <td> 603 4.8.2.7 604 </td> 605 </tr> 606 607 <tr> 608 <td> 609 B5 610 </td> 611 612 <td> 613 An instance initializer must only be invoked on an uninitialized 614 instance. 615 </td> 616 617 <td> 618 4.8.2.8 619 </td> 620 </tr> 621 622 <tr> 623 <td> 624 B6 625 </td> 626 627 <td> 628 Instance methods may only be invoked on and instance fields may only 629 be accessed on already initialized instances. 630 </td> 631 632 <td> 633 4.8.2.9 634 </td> 635 </tr> 636 637 <tr> 638 <td> 639 B7 640 </td> 641 642 <td> 643 A register which holds the result of a <code>new-instance</code>code> 644 instruction must not be used if the same 645 <code>new-instance</code>code> instruction is again executed before 646 the instance is initialized. 647 </td> 648 649 <td> 650 4.8.2.10 651 </td> 652 </tr> 653 654 <tr> 655 <td> 656 B8 657 </td> 658 659 <td> 660 An instance initializer must call another instance initializer (same 661 class or superclass) before any instance members can be accessed. 662 Exceptions are non-inherited instance fields, which can be assigned 663 before calling another initializer, and the <code>Object</code> class 664 in general. 665 </td> 666 667 <td> 668 4.8.2.11 669 </td> 670 </tr> 671 672 <tr> 673 <td> 674 B9 675 </td> 676 677 <td> 678 All actual method arguments must be assignment-compatible with their 679 respective formal arguments. 680 </td> 681 682 <td> 683 4.8.2.12 684 </td> 685 </tr> 686 687 <tr> 688 <td> 689 B10 690 </td> 691 692 <td> 693 For each instance method invocation, the actual instance must be 694 assignment-compatible with the class or interface specified in the 695 instruction. 696 </td> 697 698 <td> 699 4.8.2.13 700 </td> 701 </tr> 702 703 <tr> 704 <td> 705 B11 706 </td> 707 708 <td> 709 A <code>return<kind></code> instruction must match its 710 method's return type. 711 </td> 712 713 <td> 714 4.8.2.14 715 </td> 716 </tr> 717 718 <tr> 719 <td> 720 B12 721 </td> 722 723 <td> 724 When accessing protected members of a superclass, the actual type of 725 the instance being accessed must be either the current class or one 726 of its subclasses. 727 </td> 728 729 <td> 730 4.8.2.15 731 </td> 732 </tr> 733 734 <tr> 735 <td> 736 B13 737 </td> 738 739 <td> 740 The type of a value stored into a static field must be 741 assignment-compatible with or convertible to the field's type. 742 </td> 743 744 <td> 745 4.8.2.16 746 </td> 747 </tr> 748 749 <tr> 750 <td> 751 B14 752 </td> 753 754 <td> 755 The type of a value stored into a field must be assignment-compatible 756 with or convertible to the field's type. 757 </td> 758 759 <td> 760 4.8.2.17 761 </td> 762 </tr> 763 764 <tr> 765 <td> 766 B15 767 </td> 768 769 <td> 770 The type of every value stored into an array must be 771 assignment-compatible with the array's component type. 772 </td> 773 774 <td> 775 4.8.2.18 776 </td> 777 </tr> 778 779 <tr> 780 <td> 781 B16 782 </td> 783 784 <td> 785 The <code>A</code> operand of a <code>throw</code> instruction must 786 be assignment-compatible with <code>java.lang.Throwable</code>. 787 </td> 788 789 <td> 790 4.8.2.19 791 </td> 792 </tr> 793 794 <tr> 795 <td> 796 B17 797 </td> 798 799 <td> 800 The last reachable instruction of a method must either be a backwards 801 <code>goto</code> or branch, a <code>return</code>, or a 802 <code>throw</code> instruction. It must not be possible to leave the 803 <code>insns</code> array at the bottom. 804 </td> 805 806 <td> 807 4.8.2.20 808 </td> 809 </tr> 810 811 <tr> 812 <td> 813 B18 814 </td> 815 816 <td> 817 The unassigned half of a former register pair may not be read (is 818 considered invalid) until it has been re-assigned by some other 819 instruction. 820 </td> 821 822 <td> 823 4.8.2.3, 4.8.2.4 824 </td> 825 </tr> 826 827 <tr> 828 <td> 829 B19 830 </td> 831 832 <td> 833 A <code>move-result<kind></code> instruction must be immediately 834 preceded (in the <code>insns</code> array) by an 835 <code><invoke-kind></code> instruction. The only exception is 836 the <code>move-result-object</code> instruction, which may also be 837 preceded by a <code>filled-new-array</code> instruction. 838 </td> 839 840 <td> 841 - 842 </td> 843 </tr> 844 845 <tr> 846 <td> 847 B20 848 </td> 849 850 <td> 851 A <code>move-result<kind></code> instruction must be immediately 852 preceded (in actual control flow) by a matching 853 <code>return-<kind></code> instruction (it must not be jumped 854 to). The only exception is the <code>move-result-object</code> 855 instruction, which may also be preceded by a 856 <code>filled-new-array</code> instruction. 857 </td> 858 859 <td> 860 - 861 </td> 862 </tr> 863 864 <tr> 865 <td> 866 B21 867 </td> 868 869 <td> 870 A <code>move-exception</code> instruction must only appear as the 871 first instruction in an exception handler. 872 </td> 873 874 <td> 875 - 876 </td> 877 </tr> 878 879 <tr> 880 <td> 881 B22 882 </td> 883 884 <td> 885 The <code>packed-switch-data</code>, <code>sparse-switch-data</code>, 886 and <code>fill-array-data</code> pseudo-instructions must not be 887 reachable by control flow. 888 </td> 889 890 <td> 891 - 892 </td> 893 </tr> 894 </table> 895 896 </body> 897</html> 898