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 <div id="qv-wrapper">
 <div id="qv">
   <h2 id="Contents">In this document</h2>
   <ol id="auto-toc">
   </ol>
 </div>
 </div>

 <p>A <code>.dex</code> file is the transport format for Dalvik Bytecode. There are certain
 syntactical and semantical constraints for a file to be a valid <code>.dex</code> file, and
 a runtime is required to support only valid .dex files.</p>

     <h2 id="gen-constraints">General .dex integrity constraints</h2>

     <p>General integrity constraints are concerned with the larger structure of a
     <code>.dex</code> file, as described in detail in <a href="dex-format.html"><code>.dex</code>
     format</a>.</p>

     <table>
       <tr>
         <th>
           Identifier
         </th>

         <th>
           Description
         </th>
       </tr>

       <tr>
         <td>
           G1
         </td>

         <td>
           The <code>magic</code> number of the <code>.dex</code> file must be
           <code>dex\n035\0</code> or <code>dex\n037\0</code>.
         </td>
       </tr>

       <tr>
         <td>
           G2
         </td>

         <td>
           The checksum must be an Adler-32 checksum of the whole file contents
           except <code>magic</code> and <code>checksum</code> field.
         </td>
       </tr>

       <tr>
         <td>
           G3
         </td>

         <td>
           The signature must be a SHA-1 hash of the whole file contents except <code>magic</code>,
           <code>checksum</code>, and <code>signature</code>.
         </td>
       </tr>

       <tr>
         <td>
           G4
         </td>

         <td>
           The <code>file_size</code> must match the actual file size in bytes.
         </td>
       </tr>


       <tr>
         <td>
           G5
         </td>

         <td>
           The <code>header_size</code> must have the value: <code>0x70</code>
         </td>
       </tr>

       <tr>
         <td>
           G6
         </td>

         <td>
           The <code>endian_tag</code> must have either the value:
           <code>ENDIAN_CONSTANT</code> or <code>REVERSE_ENDIAN_CONSTANT</code>
         </td>
       </tr>

       <tr>
         <td>
           G7
         </td>

         <td>
           For each of the <code>link</code>, <code>string_ids</code>,
           <code>type_ids</code>, <code>proto_ids</code>,
           <code>field_ids</code>, <code>method_ids</code>, <code>class_defs</code>, and
           <code>data</code> sections, the <code>offset</code> and <code>size</code> fields must be
           either both zero or both non-zero. In the latter case, the offset must be
           four-byte-aligned.
         </td>
       </tr>

       <tr>
         <td>
           G8
         </td>

         <td>
           All offset fields in the header except <code>map_off</code> must be four-byte-aligned.
         </td>
       </tr>

       <tr>
         <td>
           G9
         </td>

         <td>
           The <code>map_off</code> field must be either zero or point into the
           data section. In the latter case, the <code>data</code> section must exist.
         </td>
       </tr>

       <tr>
         <td>
           G10
         </td>

         <td>
           None of the <code>link</code>, <code>string_ids</code>,
           <code>type_ids</code>, <code>proto_ids</code>, <code>field_ids</code>,
           <code>method_ids</code>, <code>class_defs</code> and <code>data</code> sections
           must overlap each other or the header.
         </td>
       </tr>

       <tr>
         <td>
           G11
         </td>

         <td>
           If a map exists, then each map entry must have a valid type. Each type may appear at most once.
         </td>
       </tr>

       <tr>
         <td>
           G12
         </td>

         <td>
           If a map exists, then each map entry must have a non-zero offset and
           size. The offset must point into the corresponding section of the file (i.e. a
           <code>string_id_item</code> must point into the <code>string_ids</code> section) and the explicit or
           implicit size of the item must match the actual contents and size of the
           section.
         </td>
       </tr>

       <tr>
         <td>
           G13
         </td>

         <td>
           If a map exists, then the offset of map entry <code>n+1</code> must be greater or
           equal to the offset of map entry <code>n plus than size of map entry n</code>. This implies
           non-overlapping entries and low-to-high ordering.
         </td>
       </tr>

       <tr>
         <td>
           G14
         </td>

         <td>
           The following types of entries must have an offset that is
           four-byte-aligned: <code>string_id_item</code>,
           <code>type_id_item</code>, <code>proto_id_item</code>,
           <code>field_id_item</code>,
           <code>method_id_item</code>, <code>class_def_item</code>,
           <code>type_list</code>, <code>code_item</code>,
           <code>annotations_directory_item</code>.
         </td>
       </tr>

       <tr>
         <td>
           G15
         </td>

         <td>
           For each <code>string_id_item</code>, the <code>string_data_off</code> field must contain a
           valid reference into the <code>data</code> section. For the referenced <code>string_data_item</code>, the
           <code>data</code> field must contain a valid MUTF-8 string, and the <code>utf16_size</code> must match
           the decoded length of the string.
         </td>
       </tr>

       <tr>
         <td>
           G16
         </td>

         <td>
           For each <code>type_id_item</code>, the <code>descriptor_idx</code> field must contain a valid
           reference into the <code>string_ids</code> list. The referenced string must be a valid type
           descriptor.
         </td>
       </tr>

       <tr>
         <td>
           G17
         </td>

         <td>
           For each <code>proto_id_item</code>, the <code>shorty_idx</code> field must contain a valid
           reference into the <code>string_ids</code> list. The referenced string must be a valid
           shorty descriptor. Also, the <code>return_type_idx</code> field must be a valid index into
           the <code>type_ids</code> section, and the <code>parameters_off</code> field must be either zero or a
           valid offset pointing into the <code>data</code> section. If non-zero, the parameter list
           must not contain any void entries.
         </td>
       </tr>

       <tr>
         <td>
           G18
         </td>

         <td>
           For each <code>field_id_item</code>, both the <code>class_idx</code> and <code>type_idx</code> fields must
           be valid indices into the <code>type_ids</code> list. The entry referenced by <code>class_idx</code>
           must be a non-array reference type. In addition, the <code>name_idx</code> field must be a
           valid reference into the <code>string_ids</code> section, and the contents of the referenced
           entry must conform to the <code>MemberName</code> specification.
         </td>
       </tr>

       <tr>
         <td>
           G19
         </td>

         <td>
           For each <code>method_id_item</code>, the <code>class_idx</code> field must be a valid index
           into the <code>type_ids</code> section, and the referenced entry must be a non-array
           reference type. The <code>proto_id</code> field must be a valid reference into the <code>proto_ids</code>
           list. The <code>name_idx</code> field must be a valid reference into the <code>string_ids</code> section,
           and the contents of the referenced entry must conform to the <code>MemberName</code>
           specification.
         </td>
       </tr>

       <tr>
         <td>
           G20
         </td>

         <td>
           For each <code>field_id_item</code>, the <code>class_idx</code> field must be a valid index
           into the <code>type_ids</code> list. The referenced entry must be a non-array reference
           type.
         </td>
       </tr>

 </table>

 <h2 id="static-constraints">
       Static bytecode 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>
       </tr>

       <tr>
         <td>
           A1
         </td>

         <td>
           The <code>insns</code> array must not be empty.
         </td>
       </tr>

       <tr>
         <td>
           A2
         </td>

         <td>
           The first opcode in the <code>insns</code> array must have index zero.
         </td>
       </tr>

       <tr>
         <td>
           A3
         </td>

         <td>
           The <code>insns</code> array must contain only valid Dalvik opcodes.
         </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>
       </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>
       </tr>

       <tr>
         <td>
           A6
         </td>

         <td>
           All <code>goto</code> and <code>if-&lt;kind&gt;</code> targets must
           be opcodes within the same method.
         </td>
       </tr>

       <tr>
         <td>
           A7
         </td>

         <td>
           All targets of a <code>packed-switch</code> instruction must be
           opcodes within the same method. The size and the list of targets
           must be consistent.
         </td>
       </tr>

       <tr>
         <td>
           A8
         </td>

         <td>
           All targets of a <code>sparse-switch</code> instruction must be
           opcodes within the same method. The corresponding table must be
           consistent and sorted low-to-high.
         </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>
       </tr>

       <tr>
         <td>
           A10
         </td>

         <td>
           The <code>C</code> operand of the <code>iget&lt;kind&gt;</code> and
           <code>iput&lt;kind&gt;</code> instructions must be a valid index into
           the field constant pool. The referenced entry must represent an
           instance field.
         </td>
       </tr>

       <tr>
         <td>
           A11
         </td>

         <td>
           The <code>C</code> operand of the <code>sget&lt;kind&gt;</code> and
           <code>sput&lt;kind&gt;</code> instructions must be a valid index into
           the field constant pool. The referenced entry must represent a static
           field.
         </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.
         </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.
         </td>
       </tr>

       <tr>
         <td>
           A14
         </td>

         <td>
           A method the name of which starts with a '&lt;' must only be invoked
           implicitly by the VM, not by code originating from a <code>.dex</code> file. The
           only exception is the instance initializer, which may be invoked by
           <code>invoke-direct</code>.
         </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>
       </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>
       </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>
       </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>
       </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>
       </tr>

       <tr>
         <td>
           A20
         </td>

         <td>
           The <code>new</code> instruction must not refer to array classes,
           interfaces, or abstract classes.
         </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>
       </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>
       </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>
       </tr>
       <tr>
         <td>
           A24
         </td>

         <td>
           The <code>method_id</code> operand of the <code>invoke-virtual</code>
           and <code>invoke-direct</code> instructions must belong to a class
           (not an interface). In Dex files prior to version <code>037</code>
           the same must be true of <code>invoke-super</code> and
           <code>invoke-static</code> instructions.
         </td>
       </tr>

       <tr>
         <td>
           A25
         </td>

         <td>
           The <code>method_id</code> operand of the
           <code>invoke-virtual/range</code> and
           <code>invoke-direct/range</code> instructions must belong to a class
           (not an interface). In Dex files prior to version <code>037</code>
           the same must be true of <code>invoke-super/range</code> and
           <code>invoke-static/range</code> instructions.
         </td>
       </tr>
     </table>

     <h2 id="struct-constraints">
       Structural bytecode 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>
       </tr>

       <tr>
         <td>
           B1
         </td>

         <td>
           The number and types of arguments (registers and immediate values)
           must always match the instruction.
         </td>
       </tr>

       <tr>
         <td>
           B2
         </td>

         <td>
           Register pairs must never be broken up.
         </td>
       </tr>

       <tr>
         <td>
           B3
         </td>

         <td>
           A register (or pair) has to be assigned first before it can be
           read.
         </td>
       </tr>

       <tr>
         <td>
           B4
         </td>

         <td>
           An <code>invoke-direct</code> instruction must invoke an instance
           initializer or a method only in the current class or one of its
           superclasses.
         </td>
       </tr>

       <tr>
         <td>
           B5
         </td>

         <td>
           An instance initializer must be invoked only on an uninitialized
           instance.
         </td>
       </tr>

       <tr>
         <td>
           B6
         </td>

         <td>
           Instance methods may be invoked only on and instance fields may only
           be accessed on already initialized instances.
         </td>
       </tr>

       <tr>
         <td>
           B7
         </td>

         <td>
           A register that 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>
       </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>
       </tr>

       <tr>
         <td>
           B9
         </td>

         <td>
            All actual method arguments must be assignment-compatible with their
            respective formal arguments.
         </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>
       </tr>

       <tr>
         <td>
           B11
         </td>

         <td>
            A <code>return&lt;kind&gt;</code> instruction must match its
            method's return type.
         </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>
       </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>
       </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>
       </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>
       </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>
       </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>
       </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>
       </tr>

       <tr>
         <td>
           B19
         </td>

         <td>
           A <code>move-result&lt;kind&gt;</code> instruction must be immediately
           preceded (in the <code>insns</code> array) by an
           <code>invoke-&lt;kind&gt;</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>
       </tr>

       <tr>
         <td>
           B20
         </td>

         <td>
           A <code>move-result&lt;kind&gt;</code> instruction must be immediately
           preceded (in actual control flow) by a matching
           <code>return-&lt;kind&gt;</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>
       </tr>

       <tr>
         <td>
           B21
         </td>

         <td>
           A <code>move-exception</code> instruction must appear only as the
           first instruction in an exception handler.
         </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>
       </tr>
     </table>
	page.title=Constraints
	@jd:body

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	<div id="qv-wrapper">
	<div id="qv">
	<h2 id="Contents">In this document</h2>
	<ol id="auto-toc">
	</ol>
	</div>
	</div>

	<p>A <code>.dex</code> file is the transport format for Dalvik Bytecode. There are certain
	syntactical and semantical constraints for a file to be a valid <code>.dex</code> file, and
	a runtime is required to support only valid .dex files.</p>

	<h2 id="gen-constraints">General .dex integrity constraints</h2>

	<p>General integrity constraints are concerned with the larger structure of a
	<code>.dex</code> file, as described in detail in <a href="dex-format.html"><code>.dex</code>
	format</a>.</p>

	<table>
	<tr>
	<th>
	Identifier
	</th>

	<th>
	Description
	</th>
	</tr>

	<tr>
	<td>
	G1
	</td>

	<td>
	The <code>magic</code> number of the <code>.dex</code> file must be
	<code>dex\n035\0</code> or <code>dex\n037\0</code>.
	</td>
	</tr>

	<tr>
	<td>
	G2
	</td>

	<td>
	The checksum must be an Adler-32 checksum of the whole file contents
	except <code>magic</code> and <code>checksum</code> field.
	</td>
	</tr>

	<tr>
	<td>
	G3
	</td>

	<td>
	The signature must be a SHA-1 hash of the whole file contents except <code>magic</code>,
	<code>checksum</code>, and <code>signature</code>.
	</td>
	</tr>

	<tr>
	<td>
	G4
	</td>

	<td>
	The <code>file_size</code> must match the actual file size in bytes.
	</td>
	</tr>


	<tr>
	<td>
	G5
	</td>

	<td>
	The <code>header_size</code> must have the value: <code>0x70</code>
	</td>
	</tr>

	<tr>
	<td>
	G6
	</td>

	<td>
	The <code>endian_tag</code> must have either the value:
	<code>ENDIAN_CONSTANT</code> or <code>REVERSE_ENDIAN_CONSTANT</code>
	</td>
	</tr>

	<tr>
	<td>
	G7
	</td>

	<td>
	For each of the <code>link</code>, <code>string_ids</code>,
	<code>type_ids</code>, <code>proto_ids</code>,
	<code>field_ids</code>, <code>method_ids</code>, <code>class_defs</code>, and
	<code>data</code> sections, the <code>offset</code> and <code>size</code> fields must be
	either both zero or both non-zero. In the latter case, the offset must be
	four-byte-aligned.
	</td>
	</tr>

	<tr>
	<td>
	G8
	</td>

	<td>
	All offset fields in the header except <code>map_off</code> must be four-byte-aligned.
	</td>
	</tr>

	<tr>
	<td>
	G9
	</td>

	<td>
	The <code>map_off</code> field must be either zero or point into the
	data section. In the latter case, the <code>data</code> section must exist.
	</td>
	</tr>

	<tr>
	<td>
	G10
	</td>

	<td>
	None of the <code>link</code>, <code>string_ids</code>,
	<code>type_ids</code>, <code>proto_ids</code>, <code>field_ids</code>,
	<code>method_ids</code>, <code>class_defs</code> and <code>data</code> sections
	must overlap each other or the header.
	</td>
	</tr>

	<tr>
	<td>
	G11
	</td>

	<td>
	If a map exists, then each map entry must have a valid type. Each type may appear at most once.
	</td>
	</tr>

	<tr>
	<td>
	G12
	</td>

	<td>
	If a map exists, then each map entry must have a non-zero offset and
	size. The offset must point into the corresponding section of the file (i.e. a
	<code>string_id_item</code> must point into the <code>string_ids</code> section) and the explicit or
	implicit size of the item must match the actual contents and size of the
	section.
	</td>
	</tr>

	<tr>
	<td>
	G13
	</td>

	<td>
	If a map exists, then the offset of map entry <code>n+1</code> must be greater or
	equal to the offset of map entry <code>n plus than size of map entry n</code>. This implies
	non-overlapping entries and low-to-high ordering.
	</td>
	</tr>

	<tr>
	<td>
	G14
	</td>

	<td>
	The following types of entries must have an offset that is
	four-byte-aligned: <code>string_id_item</code>,
	<code>type_id_item</code>, <code>proto_id_item</code>,
	<code>field_id_item</code>,
	<code>method_id_item</code>, <code>class_def_item</code>,
	<code>type_list</code>, <code>code_item</code>,
	<code>annotations_directory_item</code>.
	</td>
	</tr>

	<tr>
	<td>
	G15
	</td>

	<td>
	For each <code>string_id_item</code>, the <code>string_data_off</code> field must contain a
	valid reference into the <code>data</code> section. For the referenced <code>string_data_item</code>, the
	<code>data</code> field must contain a valid MUTF-8 string, and the <code>utf16_size</code> must match
	the decoded length of the string.
	</td>
	</tr>

	<tr>
	<td>
	G16
	</td>

	<td>
	For each <code>type_id_item</code>, the <code>descriptor_idx</code> field must contain a valid
	reference into the <code>string_ids</code> list. The referenced string must be a valid type
	descriptor.
	</td>
	</tr>

	<tr>
	<td>
	G17
	</td>

	<td>
	For each <code>proto_id_item</code>, the <code>shorty_idx</code> field must contain a valid
	reference into the <code>string_ids</code> list. The referenced string must be a valid
	shorty descriptor. Also, the <code>return_type_idx</code> field must be a valid index into
	the <code>type_ids</code> section, and the <code>parameters_off</code> field must be either zero or a
	valid offset pointing into the <code>data</code> section. If non-zero, the parameter list
	must not contain any void entries.
	</td>
	</tr>

	<tr>
	<td>
	G18
	</td>

	<td>
	For each <code>field_id_item</code>, both the <code>class_idx</code> and <code>type_idx</code> fields must
	be valid indices into the <code>type_ids</code> list. The entry referenced by <code>class_idx</code>
	must be a non-array reference type. In addition, the <code>name_idx</code> field must be a
	valid reference into the <code>string_ids</code> section, and the contents of the referenced
	entry must conform to the <code>MemberName</code> specification.
	</td>
	</tr>

	<tr>
	<td>
	G19
	</td>

	<td>
	For each <code>method_id_item</code>, the <code>class_idx</code> field must be a valid index
	into the <code>type_ids</code> section, and the referenced entry must be a non-array
	reference type. The <code>proto_id</code> field must be a valid reference into the <code>proto_ids</code>
	list. The <code>name_idx</code> field must be a valid reference into the <code>string_ids</code> section,
	and the contents of the referenced entry must conform to the <code>MemberName</code>
	specification.
	</td>
	</tr>

	<tr>
	<td>
	G20
	</td>

	<td>
	For each <code>field_id_item</code>, the <code>class_idx</code> field must be a valid index
	into the <code>type_ids</code> list. The referenced entry must be a non-array reference
	type.
	</td>
	</tr>

	</table>

	<h2 id="static-constraints">
	Static bytecode 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>
	</tr>

	<tr>
	<td>
	A1
	</td>

	<td>
	The <code>insns</code> array must not be empty.
	</td>
	</tr>

	<tr>
	<td>
	A2
	</td>

	<td>
	The first opcode in the <code>insns</code> array must have index zero.
	</td>
	</tr>

	<tr>
	<td>
	A3
	</td>

	<td>
	The <code>insns</code> array must contain only valid Dalvik opcodes.
	</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>
	</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>
	</tr>

	<tr>
	<td>
	A6
	</td>

	<td>
	All <code>goto</code> and <code>if-<kind></code> targets must
	be opcodes within the same method.
	</td>
	</tr>

	<tr>
	<td>
	A7
	</td>

	<td>
	All targets of a <code>packed-switch</code> instruction must be
	opcodes within the same method. The size and the list of targets
	must be consistent.
	</td>
	</tr>

	<tr>
	<td>
	A8
	</td>

	<td>
	All targets of a <code>sparse-switch</code> instruction must be
	opcodes within the same method. The corresponding table must be
	consistent and sorted low-to-high.
	</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>
	</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>
	</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>
	</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.
	</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.
	</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 <code>.dex</code> file. The
	only exception is the instance initializer, which may be invoked by
	<code>invoke-direct</code>.
	</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>
	</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>
	</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>
	</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>
	</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>
	</tr>

	<tr>
	<td>
	A20
	</td>

	<td>
	The <code>new</code> instruction must not refer to array classes,
	interfaces, or abstract classes.
	</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>
	</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>
	</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>
	</tr>
	<tr>
	<td>
	A24
	</td>

	<td>
	The <code>method_id</code> operand of the <code>invoke-virtual</code>
	and <code>invoke-direct</code> instructions must belong to a class
	(not an interface). In Dex files prior to version <code>037</code>
	the same must be true of <code>invoke-super</code> and
	<code>invoke-static</code> instructions.
	</td>
	</tr>

	<tr>
	<td>
	A25
	</td>

	<td>
	The <code>method_id</code> operand of the
	<code>invoke-virtual/range</code> and
	<code>invoke-direct/range</code> instructions must belong to a class
	(not an interface). In Dex files prior to version <code>037</code>
	the same must be true of <code>invoke-super/range</code> and
	<code>invoke-static/range</code> instructions.
	</td>
	</tr>
	</table>

	<h2 id="struct-constraints">
	Structural bytecode 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>
	</tr>

	<tr>
	<td>
	B1
	</td>

	<td>
	The number and types of arguments (registers and immediate values)
	must always match the instruction.
	</td>
	</tr>

	<tr>
	<td>
	B2
	</td>

	<td>
	Register pairs must never be broken up.
	</td>
	</tr>

	<tr>
	<td>
	B3
	</td>

	<td>
	A register (or pair) has to be assigned first before it can be
	read.
	</td>
	</tr>

	<tr>
	<td>
	B4
	</td>

	<td>
	An <code>invoke-direct</code> instruction must invoke an instance
	initializer or a method only in the current class or one of its
	superclasses.
	</td>
	</tr>

	<tr>
	<td>
	B5
	</td>

	<td>
	An instance initializer must be invoked only on an uninitialized
	instance.
	</td>
	</tr>

	<tr>
	<td>
	B6
	</td>

	<td>
	Instance methods may be invoked only on and instance fields may only
	be accessed on already initialized instances.
	</td>
	</tr>

	<tr>
	<td>
	B7
	</td>

	<td>
	A register that 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>
	</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>
	</tr>

	<tr>
	<td>
	B9
	</td>

	<td>
	All actual method arguments must be assignment-compatible with their
	respective formal arguments.
	</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>
	</tr>

	<tr>
	<td>
	B11
	</td>

	<td>
	A <code>return<kind></code> instruction must match its
	method's return type.
	</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>
	</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>
	</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>
	</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>
	</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>
	</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>
	</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>
	</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>
	</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>
	</tr>

	<tr>
	<td>
	B21
	</td>

	<td>
	A <code>move-exception</code> instruction must appear only as the
	first instruction in an exception handler.
	</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>
	</tr>
	</table>