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| <head> |
| <title>Dalvik bytecode constraints</title> |
| <link rel=stylesheet href="dalvik-constraints.css"> |
| </head> |
| |
| <body> |
| |
| <h1>Dalvik bytecode constraints</h1> |
| |
| <!-- |
| <h1>General integrity constraints</h1> |
| |
| <table> |
| <tr> |
| <th> |
| Identifier |
| </th> |
| |
| <th> |
| Description |
| </th> |
| </tr> |
| |
| <tr> |
| <td> |
| A1 |
| </td> |
| |
| <td> |
| The magic number of the DEX file must be "dex\n035\0". |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A1 |
| </td> |
| |
| <td> |
| The checksum must be an Adler-32 checksum of the whole file contents |
| except magic and checksum field. |
| </td> |
| </tr> |
| |
| |
| The signature must be a SHA-1 hash of the whole file contents except magic, |
| checksum, and signature. |
| |
| The file_size must match the actual file size in bytes. |
| |
| The header_size must have the value 0x70. |
| |
| The endian_tag must have either the value ENDIAN_CONSTANT or |
| REVERSE_ENDIAN_CONSTANT. |
| |
| For each of the link, string_ids, type_ids, proto_ids, field_ids, method_ids, class_defs |
| and data sections, the offset and size fields must be either both zero or both |
| non-zero. In the latter case, the offset must be four-byte-aligned. |
| |
| All offset fields in the header except map_off must be four-byte-aligned. |
| |
| The map_off field must be either zero or point into the data section. In the |
| latter case, the data section must exist. |
| |
| None of the link, string_ids, type_ids, proto_ids, field_ids, method_ids, class_defs |
| and data sections must overlap each other or the header. |
| |
| If a map exists, then each map entry must have a valid type. Each type may |
| appear at most once. |
| |
| If a map exists, then each map entry must have a nonzero offset and size. The |
| offset must point into the corresponding section of the file (i.e. a |
| string_id_item must point into the string_ids section) and the explicit or |
| implicit size of the item must match the actual contents and size of the |
| section. |
| |
| If a map exists, then the offset of map entry n+1 must be greater or equal to |
| the offset of map entry n plus then size of map entry n. This implies |
| non-overlapping entries and low-to-high ordering. |
| |
| The following types of entries must have an offset that is |
| four-byte-aligned: string_id_item, type_id_item, proto_id_item, field_id_item, |
| method_id_item, class_def_item, type_list, code_item, |
| annotations_directory_item. |
| |
| For each string_id_item, the string_data_off field must contain a valid |
| reference into the data section. For the referenced string_data_item, the data |
| field must contain a valid MUTF-8 string, and the utf16_size must match the |
| decoded length of the string. |
| |
| For each type_id_item, the desciptor_idx field must contain a valid reference |
| into the string_ids list. The referenced string must be a valid type descriptor. |
| |
| For each proto_id_item, the shorty_idx field must contain a valid reference |
| into the string_ids list. The referenced string must be a valid shorty descriptor. |
| Also, the return_type_idx field must be a valid index into the type_ids section, |
| and the parameters_off field must be either zero or a valid offset pointing |
| into the data section. If nonzero, the parameter list must not contain any void |
| entries. |
| |
| For each field_id_item, both the class_idx and type_idx fields must be a valid |
| indices into the |
| type_ids list. The entry referenced by class_idx must be a non-array reference type. |
| In addition, the name_idx field must be a valid reference into the string_ids |
| section, and the contents of the referenced entry must conform to the MemberName |
| specification. |
| |
| For each method_id_item, the class_idx field must be a valid index into the |
| type_ids section, and the |
| referenced entry must be a non-array reference type. The proto_id field must |
| be a valid reference into the proto_ids list. The name_idx field must be a |
| valid reference into the string_ids |
| section, and the contents of the referenced entry must conform to the MemberName |
| specification. |
| |
| For each class_def_item, ... |
| |
| For each field_id_item, the class_idx field must be a valid index into the |
| type_ids list. The referenced entry must be a non-array reference type. |
| |
| ... |
| |
| --> |
| |
| <h2> |
| Static constraints |
| </h2> |
| |
| <p> |
| Static constraints are constraints on individual elements of the bytecode. |
| They usually can be checked without employing control or data-flow analysis |
| techniques. |
| </p> |
| |
| <table> |
| <tr> |
| <th> |
| Identifier |
| </th> |
| |
| <th> |
| Description |
| </th> |
| |
| <th> |
| Spec equivalent |
| </th> |
| </tr> |
| |
| <tr> |
| <td> |
| A1 |
| </td> |
| |
| <td> |
| The <code>insns</code> array must not be empty. |
| </td> |
| |
| <td> |
| 4.8.1.1 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A2 |
| </td> |
| |
| <td> |
| The first opcode in the <code>insns</code> array must have index zero. |
| </td> |
| |
| <td> |
| 4.8.1.3 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A3 |
| </td> |
| |
| <td> |
| The <code>insns</code> array must only contain valid Dalvik opcodes. |
| </td> |
| |
| <td> |
| 4.8.1.4 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A4 |
| </td> |
| |
| <td> |
| The index of instruction <code>n+1</code> must equal the index of |
| instruction <code>n</code> plus the length of instruction |
| <code>n</code>, taking into account possible operands. |
| </td> |
| |
| <td> |
| 4.8.1.5 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A5 |
| </td> |
| |
| <td> |
| The last instruction in the <code>insns</code> array must end at index |
| <code>insns_size-1</code>. |
| </td> |
| |
| <td> |
| 4.8.1.6 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A6 |
| </td> |
| |
| <td> |
| All <code>goto</code> and <code>if-<kind></code> targets must |
| be opcodes within in the same method. |
| </td> |
| |
| <td> |
| 4.8.1.7 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A7 |
| </td> |
| |
| <td> |
| All targets of a <code>packed-switch</code> instruction must be |
| opcodes within in the same method. The size and the list of targets |
| must be consistent. |
| </td> |
| |
| <td> |
| 4.8.1.8 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A8 |
| </td> |
| |
| <td> |
| All targets of a <code>sparse-switch</code> instruction must be |
| opcodes within in the same method. The corresponding table must be |
| consistent and sorted low-to-high. |
| </td> |
| |
| <td> |
| 4.8.1.9 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A9 |
| </td> |
| |
| <td> |
| The <code>B</code> operand of the <code>const-string</code> and |
| <code>const-string/jumbo</code> instructions must be a valid index |
| into the string constant pool. |
| </td> |
| |
| <td> |
| 4.8.1.10 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A10 |
| </td> |
| |
| <td> |
| The <code>C</code> operand of the <code>iget<kind></code> and |
| <code>iput<kind></code> instructions must be a valid index into |
| the field constant pool. The referenced entry must represent an |
| instance field. |
| </td> |
| |
| <td> |
| 4.8.1.12 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A11 |
| </td> |
| |
| <td> |
| The <code>C</code> operand of the <code>sget<kind></code> and |
| <code>sput<kind></code> instructions must be a valid index into |
| the field constant pool. The referenced entry must represent a static |
| field. |
| </td> |
| |
| <td> |
| 4.8.1.12 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A12 |
| </td> |
| |
| <td> |
| The <code>C</code> operand of the <code>invoke-virtual</code>, |
| <code>invoke-super</code>, <code<invoke-direct</code> and |
| <code>invoke-static</code> instructions must be a valid index into the |
| method constant pool. In all cases, the referenced |
| <code>method_id</code> must belong to a class (not an interface). |
| </td> |
| |
| <td> |
| 4.8.1.13 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A13 |
| </td> |
| |
| <td> |
| The <code>B</code> operand of the <code>invoke-virtual/range</code>, |
| <code>invoke-super/range</code>, <code>invoke-direct/range</code>, and |
| <code>invoke-static/range</code> instructions must be a valid index |
| into the method constant pool. In all cases, the referenced |
| <code>method_id</code> must belong to a class (not an interface). |
| </td> |
| |
| <td> |
| 4.8.1.13 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A14 |
| </td> |
| |
| <td> |
| A method the name of which starts with a '<' must only be invoked |
| implicitly by the VM, not by code originating from a Dex file. The |
| only exception is the instance initializer, which may be invoked by |
| <code>invoke-direct</code>. |
| </td> |
| |
| <td> |
| 4.8.1.14 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A15 |
| </td> |
| |
| <td> |
| The <code>C</code> operand of the <code>invoke-interface</code> |
| instruction must be a valid index into the method constant pool. The |
| referenced <code>method_id</code> must belong to an interface (not a |
| class). |
| </td> |
| |
| <td> |
| 4.8.1.15 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A16 |
| </td> |
| |
| <td> |
| The <code>B</code> operand of the <code>invoke-interface/range</code> |
| instruction must be a valid index into the method constant pool. |
| The referenced <code>method_id</code> must belong to an interface (not |
| a class). |
| </td> |
| |
| <td> |
| 4.8.1.15 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A17 |
| </td> |
| |
| <td> |
| The <code>B</code> operand of the <code>const-class</code>, |
| <code>check-cast</code>, <code>new-instance</code>, and |
| <code>filled-new-array/range</code> instructions must be a valid index |
| into the type constant pool. |
| </td> |
| |
| <td> |
| 4.8.1.16 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A18 |
| </td> |
| |
| <td> |
| The <code>C</code> operand of the <code>instance-of</code>, |
| <code>new-array</code>, and <code>filled-new-array</code> |
| instructions must be a valid index into the type constant pool. |
| </td> |
| |
| <td> |
| 4.8.1.16 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A19 |
| </td> |
| |
| <td> |
| The dimensions of an array created by a <code>new-array</code> |
| instruction must be less than <code>256</code>. |
| </td> |
| |
| <td> |
| 4.8.1.17 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A20 |
| </td> |
| |
| <td> |
| The <code>new</code> instruction must not refer to array classes, |
| interfaces, or abstract classes. |
| </td> |
| |
| <td> |
| 4.8.1.18 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A21 |
| </td> |
| |
| <td> |
| The type referred to by a <code>new-array</code> instruction must be |
| a valid, non-reference type. |
| </td> |
| |
| <td> |
| 4.8.1.20 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A22 |
| </td> |
| |
| <td> |
| All registers referred to by an instruction in a single-width |
| (non-pair) fashion must be valid for the current method. That is, |
| their indices must be non-negative and smaller than |
| <code>registers_size</code>. |
| </td> |
| |
| <td> |
| 4.8.1.21 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| A23 |
| </td> |
| |
| <td> |
| All registers referred to by an instruction in a double-width (pair) |
| fashion must be valid for the current method. That is, their indices |
| must be non-negative and smaller than <code>registers_size-1</code>. |
| </td> |
| |
| <td> |
| 4.8.1.23 |
| </td> |
| </tr> |
| </table> |
| |
| <h2> |
| Structural constraints |
| </h2> |
| |
| <p> |
| Structural constraints are constraints on relationships between several |
| elements of the bytecode. They usually can't be checked without employing |
| control or data-flow analysis techniques. |
| </p> |
| |
| <table> |
| <tr> |
| <th> |
| Identifier |
| </th> |
| |
| <th> |
| Description |
| </th> |
| |
| <th> |
| Spec equivalent |
| </th> |
| </tr> |
| |
| <tr> |
| <td> |
| B1 |
| </td> |
| |
| <td> |
| The number and types of arguments (registers and immediate values) |
| must always match the instruction. |
| </td> |
| |
| <td> |
| 4.8.2.1 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B2 |
| </td> |
| |
| <td> |
| Register pairs must never be broken up. |
| </td> |
| |
| <td> |
| 4.8.2.3 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B3 |
| </td> |
| |
| <td> |
| A register (or pair) has to be assigned first before it can be |
| read. |
| </td> |
| |
| <td> |
| 4.8.2.4 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B4 |
| </td> |
| |
| <td> |
| An <code>invoke-direct</code> instruction must only invoke an instance |
| initializer or a method in the current class or one of its |
| superclasses. |
| </td> |
| |
| <td> |
| 4.8.2.7 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B5 |
| </td> |
| |
| <td> |
| An instance initializer must only be invoked on an uninitialized |
| instance. |
| </td> |
| |
| <td> |
| 4.8.2.8 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B6 |
| </td> |
| |
| <td> |
| Instance methods may only be invoked on and instance fields may only |
| be accessed on already initialized instances. |
| </td> |
| |
| <td> |
| 4.8.2.9 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B7 |
| </td> |
| |
| <td> |
| A register which holds the result of a <code>new-instance</code> |
| instruction must not be used if the same |
| <code>new-instance</code> instruction is again executed before |
| the instance is initialized. |
| </td> |
| |
| <td> |
| 4.8.2.10 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B8 |
| </td> |
| |
| <td> |
| An instance initializer must call another instance initializer (same |
| class or superclass) before any instance members can be accessed. |
| Exceptions are non-inherited instance fields, which can be assigned |
| before calling another initializer, and the <code>Object</code> class |
| in general. |
| </td> |
| |
| <td> |
| 4.8.2.11 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B9 |
| </td> |
| |
| <td> |
| All actual method arguments must be assignment-compatible with their |
| respective formal arguments. |
| </td> |
| |
| <td> |
| 4.8.2.12 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B10 |
| </td> |
| |
| <td> |
| For each instance method invocation, the actual instance must be |
| assignment-compatible with the class or interface specified in the |
| instruction. |
| </td> |
| |
| <td> |
| 4.8.2.13 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B11 |
| </td> |
| |
| <td> |
| A <code>return<kind></code> instruction must match its |
| method's return type. |
| </td> |
| |
| <td> |
| 4.8.2.14 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B12 |
| </td> |
| |
| <td> |
| When accessing protected members of a superclass, the actual type of |
| the instance being accessed must be either the current class or one |
| of its subclasses. |
| </td> |
| |
| <td> |
| 4.8.2.15 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B13 |
| </td> |
| |
| <td> |
| The type of a value stored into a static field must be |
| assignment-compatible with or convertible to the field's type. |
| </td> |
| |
| <td> |
| 4.8.2.16 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B14 |
| </td> |
| |
| <td> |
| The type of a value stored into a field must be assignment-compatible |
| with or convertible to the field's type. |
| </td> |
| |
| <td> |
| 4.8.2.17 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B15 |
| </td> |
| |
| <td> |
| The type of every value stored into an array must be |
| assignment-compatible with the array's component type. |
| </td> |
| |
| <td> |
| 4.8.2.18 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B16 |
| </td> |
| |
| <td> |
| The <code>A</code> operand of a <code>throw</code> instruction must |
| be assignment-compatible with <code>java.lang.Throwable</code>. |
| </td> |
| |
| <td> |
| 4.8.2.19 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B17 |
| </td> |
| |
| <td> |
| The last reachable instruction of a method must either be a backwards |
| <code>goto</code> or branch, a <code>return</code>, or a |
| <code>throw</code> instruction. It must not be possible to leave the |
| <code>insns</code> array at the bottom. |
| </td> |
| |
| <td> |
| 4.8.2.20 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B18 |
| </td> |
| |
| <td> |
| The unassigned half of a former register pair may not be read (is |
| considered invalid) until it has been re-assigned by some other |
| instruction. |
| </td> |
| |
| <td> |
| 4.8.2.3, 4.8.2.4 |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B19 |
| </td> |
| |
| <td> |
| A <code>move-result<kind></code> instruction must be immediately |
| preceded (in the <code>insns</code> array) by an |
| <code>invoke-<kind></code> instruction. The only exception is |
| the <code>move-result-object</code> instruction, which may also be |
| preceded by a <code>filled-new-array</code> instruction. |
| </td> |
| |
| <td> |
| - |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B20 |
| </td> |
| |
| <td> |
| A <code>move-result<kind></code> instruction must be immediately |
| preceded (in actual control flow) by a matching |
| <code>return-<kind></code> instruction (it must not be jumped |
| to). The only exception is the <code>move-result-object</code> |
| instruction, which may also be preceded by a |
| <code>filled-new-array</code> instruction. |
| </td> |
| |
| <td> |
| - |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B21 |
| </td> |
| |
| <td> |
| A <code>move-exception</code> instruction must only appear as the |
| first instruction in an exception handler. |
| </td> |
| |
| <td> |
| - |
| </td> |
| </tr> |
| |
| <tr> |
| <td> |
| B22 |
| </td> |
| |
| <td> |
| The <code>packed-switch-data</code>, <code>sparse-switch-data</code>, |
| and <code>fill-array-data</code> pseudo-instructions must not be |
| reachable by control flow. |
| </td> |
| |
| <td> |
| - |
| </td> |
| </tr> |
| </table> |
| |
| </body> |
| </html> |