Android Dex文件结构

dex— Dalvik Executable Format

Copyright © 2007 The Android Open Source Project

This document describes the layout and contents of.dexfiles, which are used to hold a set of class definitions and their associated adjunct data.

Guide To Types

Name	Description
byte	8-bit signed int
ubyte	8-bit unsigned int
short	16-bit signed int, little-endian
ushort	16-bit unsigned int, little-endian
int	32-bit signed int, little-endian
uint	32-bit unsigned int, little-endian
long	64-bit signed int, little-endian
ulong	64-bit unsigned int, little-endian
sleb128	signed LEB128, variable-length (see below)
uleb128	unsigned LEB128, variable-length (see below)
uleb128p1	unsigned LEB128 plus1, variable-length (see below)

LEB128

LEB128 ("Little-EndianBase128") is a variable-length encoding for arbitrary signed or unsigned integer quantities. The format was borrowed from theDWARF3specification. In a.dexfile, LEB128 is only ever used to encode 32-bit quantities.

Each LEB128 encoded value consists of one to five bytes, which together represent a single 32-bit value. Each byte has its most significant bit set except for the final byte in the sequence, which has its most significant bit clear. The remaining seven bits of each byte are payload, with the least significant seven bits of the quantity in the first byte, the next seven in the second byte and so on. In the case of a signed LEB128 (sleb128), the most significant payload bit of the final byte in the sequence is sign-extended to produce the final value. In the unsigned case (uleb128), any bits not explicitly represented are interpreted as0.

Bitwise diagram of a two-byte LEB128 value

First byte

Second byte

1

bit6

bit5

bit4

bit3

bit2

bit1

bit0

0

bit13

bit12

bit11

bit10

bit9

bit8

bit7

The variantuleb128p1is used to represent a signed value, where the representation is of the valueplus oneencoded as auleb128. This makes the encoding of-1(alternatively thought of as the unsigned value0xffffffff) — but no other negative number — a single byte, and is useful in exactly those cases where the represented number must either be non-negative or-1(or0xffffffff), and where no other negative values are allowed (or where large unsigned values are unlikely to be needed).

Here are some examples of the formats:

Encoded Sequence	Assleb128	Asuleb128	Asuleb128p1
00	0	0	-1
01	1	1	0
7f	-1	127	126
80 7f	-128	16256	16255

Overall File Layout

Name	Format	Description
header	header_item	the header
string_ids	string_id_item[]	string identifiers list. These are identifiers for all the strings used by this file, either for internal naming (e.g., type descriptors) or as constant objects referred to by code. This list must be sorted by string contents, using UTF-16 code point values (not in a locale-sensitive manner).
type_ids	type_id_item[]	type identifiers list. These are identifiers for all types (classes, arrays, or primitive types) referred to by this file, whether defined in the file or not. This list must be sorted bystring_idindex.
proto_ids	proto_id_item[]	method prototype identifiers list. These are identifiers for all prototypes referred to by this file. This list must be sorted in return-type (bytype_idindex) major order, and then by arguments (also bytype_idindex).
field_ids	field_id_item[]	field identifiers list. These are identifiers for all fields referred to by this file, whether defined in the file or not. This list must be sorted, where the defining type (bytype_idindex) is the major order, field name (bystring_idindex) is the intermediate order, and type (bytype_idindex) is the minor order.
method_ids	method_id_item[]	method identifiers list. These are identifiers for all methods referred to by this file, whether defined in the file or not. This list must be sorted, where the defining type (bytype_idindex) is the major order, method name (bystring_idindex) is the intermediate order, and method prototype (byproto_idindex) is the minor order.
class_defs	class_def_item[]	class definitions list. The classes must be ordered such that a given class's superclass and implemented interfaces appear in the list earlier than the referring class.
data	ubyte[]	data area, containing all the support data for the tables listed above. Different items have different alignment requirements, and padding bytes are inserted before each item if necessary to achieve proper alignment.
link_data	ubyte[]	data used in statically linked files. The format of the data in this section is left unspecified by this document; this section is empty in unlinked files, and runtime implementations may use it as they see fit.

Bitfield, String, and Constant Definitions

DEX_FILE_MAGIC

embedded inheader_item

The constant array/stringDEX_FILE_MAGICis the list of bytes that must appear at the beginning of a.dexfile in order for it to be recognized as such. The value intentionally contains a newline ("/n"or0x0a) and a null byte ("/0"or0x00) in order to help in the detection of certain forms of corruption. The value also encodes a format version number as three decimal digits, which is expected to increase monotonically over time as the format evolves.

ubyte[8] DEX_FILE_MAGIC = { 0x64 0x65 0x78 0x0a 0x30 0x33 0x35 0x00 }

= "dex/n035/0"

Note:At least a couple earlier versions of the format have been used in widely-available public software releases. For example, version009was used for the M3 releases of the Android platform (November-December 2007), and version013was used for the M5 releases of the Android platform (February-March 2008). In several respects, these earlier versions of the format differ significantly from the version described in this document.

ENDIAN_CONSTANTandREVERSE_ENDIAN_CONSTANT

embedded inheader_item

The constantENDIAN_CONSTANTis used to indicate the endianness of the file in which it is found. Although the standard.dexformat is little-endian, implementations may choose to perform byte-swapping. Should an implementation come across a header whoseendian_tagisREVERSE_ENDIAN_CONSTANTinstead ofENDIAN_CONSTANT, it would know that the file has been byte-swapped from the expected form.

uint ENDIAN_CONSTANT = 0x12345678;

uint REVERSE_ENDIAN_CONSTANT = 0x78563412;

NO_INDEX

embedded inclass_def_itemanddebug_info_item

The constantNO_INDEXis used to indicate that an index value is absent.

Note:This value isn't defined to be0, because that is in fact typically a valid index.

Also Note:The chosen value forNO_INDEXis representable as a single byte in theuleb128p1encoding.

uint NO_INDEX = 0xffffffff; // == -1 if treated as a signed int

access_flagsDefinitions

embedded inclass_def_item,field_item,method_item, andInnerClass

Bitfields of these flags are used to indicate the accessibility and overall properties of classes and class members.

Name	Value	For Classes (andInnerClassannotations)	For Fields	For Methods
ACC_PUBLIC	0x1	public: visible everywhere	public: visible everywhere	public: visible everywhere
ACC_PRIVATE	0x2	*private: only visible to defining class	private: only visible to defining class	private: only visible to defining class
ACC_PROTECTED	0x4	*protected: visible to package and subclasses	protected: visible to package and subclasses	protected: visible to package and subclasses
ACC_STATIC	0x8	*static: is not constructed with an outerthisreference	static: global to defining class	static: does not take athisargument
ACC_FINAL	0x10	final: not subclassable	final: immutable after construction	final: not overridable
ACC_SYNCHRONIZED	0x20			synchronized: associated lock automatically acquired around call to this method.Note:This is only valid to set whenACC_NATIVEis also set.
ACC_VOLATILE	0x40		volatile: special access rules to help with thread safety
ACC_BRIDGE	0x40			bridge method, added automatically by compiler as a type-safe bridge
ACC_TRANSIENT	0x80		transient: not to be saved by default serialization
ACC_VARARGS	0x80			last argument should be treated as a "rest" argument by compiler
ACC_NATIVE	0x100			native: implemented in native code
ACC_INTERFACE	0x200	interface: multiply-implementable abstract class
ACC_ABSTRACT	0x400	abstract: not directly instantiable		abstract: unimplemented by this class
ACC_STRICT	0x800			strictfp: strict rules for floating-point arithmetic
ACC_SYNTHETIC	0x1000	not directly defined in source code	not directly defined in source code	not directly defined in source code
ACC_ANNOTATION	0x2000	declared as an annotation class
ACC_ENUM	0x4000	declared as an enumerated type	declared as an enumerated value
(unused)	0x8000
ACC_CONSTRUCTOR	0x10000			constructor method (class or instance initializer)
ACC_DECLARED_ SYNCHRONIZED	0x20000			declaredsynchronized.Note:This has no effect on execution (other than in reflection of this flag, per se).

*Only allowed on forInnerClassannotations, and must not ever be on in aclass_def_item.

MUTF-8 (Modified UTF-8) Encoding

As a concession to easier legacy support, the.dexformat encodes its string data in a de facto standard modified UTF-8 form, hereafter referred to as MUTF-8. This form is identical to standard UTF-8, except:

• Only the one-, two-, and three-byte encodings are used.
• Code points in the rangeU+10000…U+10ffffare encoded as a surrogate pair, each of which is represented as a three-byte encoded value.
• The code pointU+0000is encoded in two-byte form.
• A plain null byte (value0) indicates the end of a string, as is the standard C language interpretation.

The first two items above can be summarized as: MUTF-8 is an encoding format for UTF-16, instead of being a more direct encoding format for Unicode characters.

The final two items above make it simultaneously possible to include the code pointU+0000in a stringandstill manipulate it as a C-style null-terminated string.

However, the special encoding ofU+0000means that, unlike normal UTF-8, the result of calling the standard C functionstrcmp()on a pair of MUTF-8 strings does not always indicate the properly signed result of comparison ofunequalstrings. When ordering (not just equality) is a concern, the most straightforward way to compare MUTF-8 strings is to decode them character by character, and compare the decoded values. (However, more clever implementations are also possible.)

Please refer toThe Unicode Standardfor further information about character encoding. MUTF-8 is actually closer to the (relatively less well-known) encodingCESU-8than to UTF-8 per se.

encoded_valueEncoding

embedded inannotation_elementandencoded_array_item

Anencoded_valueis an encoded piece of (nearly) arbitrary hierarchically structured data. The encoding is meant to be both compact and straightforward to parse.

Name	Format	Description
(value_arg << 5) | value_type	ubyte	byte indicating the type of the immediately subsequentvaluealong with an optional clarifying argument in the high-order three bits. See below for the variousvaluedefinitions. In most cases,value_argencodes the length of the immediately-subsequentvaluein bytes, as(size - 1), e.g.,0means that the value requires one byte, and7means it requires eight bytes; however, there are exceptions as noted below.
value	ubyte[]	bytes representing the value, variable in length and interpreted differently for differentvalue_typebytes, though always little-endian. See the various value definitions below for details.

Value Formats

Type Name	value_type	value_argFormat	valueFormat	Description
VALUE_BYTE	0x00	(none; must be0)	ubyte[1]	signed one-byte integer value
VALUE_SHORT	0x02	size - 1 (0…1)	ubyte[size]	signed two-byte integer value, sign-extended
VALUE_CHAR	0x03	size - 1 (0…1)	ubyte[size]	unsigned two-byte integer value, zero-extended
VALUE_INT	0x04	size - 1 (0…3)	ubyte[size]	signed four-byte integer value, sign-extended
VALUE_LONG	0x06	size - 1 (0…7)	ubyte[size]	signed eight-byte integer value, sign-extended
VALUE_FLOAT	0x10	size - 1 (0…3)	ubyte[size]	four-byte bit pattern, zero-extendedto the right, and interpreted as an IEEE754 32-bit floating point value
VALUE_DOUBLE	0x11	size - 1 (0…7)	ubyte[size]	eight-byte bit pattern, zero-extendedto the right, and interpreted as an IEEE754 64-bit floating point value
VALUE_STRING	0x17	size - 1 (0…3)	ubyte[size]	unsigned (zero-extended) four-byte integer value, interpreted as an index into thestring_idssection and representing a string value
VALUE_TYPE	0x18	size - 1 (0…3)	ubyte[size]	unsigned (zero-extended) four-byte integer value, interpreted as an index into thetype_idssection and representing a reflective type/class value
VALUE_FIELD	0x19	size - 1 (0…3)	ubyte[size]	unsigned (zero-extended) four-byte integer value, interpreted as an index into thefield_idssection and representing a reflective field value
VALUE_METHOD	0x1a	size - 1 (0…3)	ubyte[size]	unsigned (zero-extended) four-byte integer value, interpreted as an index into themethod_idssection and representing a reflective method value
VALUE_ENUM	0x1b	size - 1 (0…3)	ubyte[size]	unsigned (zero-extended) four-byte integer value, interpreted as an index into thefield_idssection and representing the value of an enumerated type constant
VALUE_ARRAY	0x1c	(none; must be0)	encoded_array	an array of values, in the format specified by "encoded_arrayFormat" below. The size of thevalueis implicit in the encoding.
VALUE_ANNOTATION	0x1d	(none; must be0)	encoded_annotation	a sub-annotation, in the format specified by "encoded_annotationFormat" below. The size of thevalueis implicit in the encoding.
VALUE_NULL	0x1e	(none; must be0)	(none)	nullreference value
VALUE_BOOLEAN	0x1f	boolean (0…1)	(none)	one-bit value;0forfalseand1fortrue. The bit is represented in thevalue_arg.

encoded_arrayFormat

Name	Format	Description
size	uleb128	number of elements in the array
values	encoded_value[size]	a series ofsizeencoded_valuebyte sequences in the format specified by this section, concatenated sequentially.

encoded_annotationFormat

Name	Format	Description
type_idx	uleb128	type of the annotation. This must be a class (not array or primitive) type.
size	uleb128	number of name-value mappings in this annotation
elements	annotation_element[size]	elements of the annotataion, represented directly in-line (not as offsets). Elements must be sorted in increasing order bystring_idindex.

annotation_elementFormat

Name	Format	Description
name_idx	uleb128	element name, represented as an index into thestring_idssection. The string must conform to the syntax forMemberName, defined above.
value	encoded_value	element value

String Syntax

There are several kinds of item in a.dexfile which ultimately refer to a string. The following BNF-style definitions indicate the acceptable syntax for these strings.

SimpleName

ASimpleNameis the basis for the syntax of the names of other things. The.dexformat allows a fair amount of latitude here (much more than most common source languages). In brief, a simple name may consist of any low-ASCII alphabetic character or digit, a few specific low-ASCII symbols, and most non-ASCII code points that are not control, space, or special characters. Note that surrogate code points (in the rangeU+d800…U+dfff) are not considered valid name characters, per se, but Unicode supplemental charactersarevalid (which are represented by the final alternative of the rule forSimpleNameChar), and they should be represented in a file as pairs of surrogate code points in the MUTF-8 encoding.

SimpleName→
	SimpleNameChar(SimpleNameChar)*
SimpleNameChar→
	'A'…'Z'
|	'a'…'z'
|	'0'…'9'
|	'$'
|	'-'
|	'_'
|	U+00a1…U+1fff
|	U+2010…U+2027
|	U+2030…U+d7ff
|	U+e000…U+ffef
|	U+10000…U+10ffff

MemberName

used byfield_id_itemandmethod_id_item

AMemberNameis the name of a member of a class, members being fields, methods, and inner classes.

MemberName→
	SimpleName
|	'<'SimpleName'>'

FullClassName

AFullClassNameis a fully-qualified class name, including an optional package specifier followed by a required name.

FullClassName→
	OptionalPackagePrefixSimpleName
OptionalPackagePrefix→
	(SimpleName'/')*

TypeDescriptor

used bytype_id_item

ATypeDescriptoris the representation of any type, including primitives, classes, arrays, andvoid. See below for the meaning of the various versions.

TypeDescriptor→
	'V'
|	FieldTypeDescriptor
FieldTypeDescriptor→
	NonArrayFieldTypeDescriptor
|	('['* 1…255)NonArrayFieldTypeDescriptor
NonArrayFieldTypeDescriptor→
	'Z'
|	'B'
|	'S'
|	'C'
|	'I'
|	'J'
|	'F'
|	'D'
|	'L'FullClassName';'

ShortyDescriptor

used byproto_id_item

AShortyDescriptoris the short form representation of a method prototype, including return and parameter types, except that there is no distinction between various reference (class or array) types. Instead, all reference types are represented by a single'L'character.

ShortyDescriptor→
	ShortyReturnType(ShortyFieldType)*
ShortyReturnType→
	'V'
|	ShortyFieldType
ShortyFieldType→
	'Z'
|	'B'
|	'S'
|	'C'
|	'I'
|	'J'
|	'F'
|	'D'
|	'L'

TypeDescriptorSemantics

This is the meaning of each of the variants ofTypeDescriptor.

Syntax	Meaning
V	void; only valid for return types
Z	boolean
B	byte
S	short
C	char
I	int
J	long
F	float
D	double
Lfully/qualified/Name;	the classfully.qualified.Name
[descriptor	array ofdescriptor, usable recursively for arrays-of-arrays, though it is invalid to have more than 255 dimensions.

Items and Related Structures

This section includes definitions for each of the top-level items that may appear in a.dexfile.

header_item

appears in theheadersection

alignment: 4 bytes

Name	Format	Description
magic	ubyte[8] = DEX_FILE_MAGIC	magic value. See discussion above under "DEX_FILE_MAGIC" for more details.
checksum	uint	adler32 checksum of the rest of the file (everything butmagicand this field); used to detect file corruption
signature	ubyte[20]	SHA-1 signature (hash) of the rest of the file (everything butmagic,checksum, and this field); used to uniquely identify files
file_size	uint	size of the entire file (including the header), in bytes
header_size	uint = 0x70	size of the header (this entire section), in bytes. This allows for at least a limited amount of backwards/forwards compatibility without invalidating the format.
endian_tag	uint = ENDIAN_CONSTANT	endianness tag. See discussion above under "ENDIAN_CONSTANTandREVERSE_ENDIAN_CONSTANT" for more details.
link_size	uint	size of the link section, or0if this file isn't statically linked
link_off	uint	offset from the start of the file to the link section, or0iflink_size == 0. The offset, if non-zero, should be to an offset into thelink_datasection. The format of the data pointed at is left unspecified by this document; this header field (and the previous) are left as hooks for use by runtime implementations.
map_off	uint	offset from the start of the file to the map item, or0if this file has no map. The offset, if non-zero, should be to an offset into thedatasection, and the data should be in the format specified by "map_list" below.
string_ids_size	uint	count of strings in the string identifiers list
string_ids_off	uint	offset from the start of the file to the string identifiers list, or0ifstring_ids_size == 0(admittedly a strange edge case). The offset, if non-zero, should be to the start of thestring_idssection.
type_ids_size	uint	count of elements in the type identifiers list
type_ids_off	uint	offset from the start of the file to the type identifiers list, or0iftype_ids_size == 0(admittedly a strange edge case). The offset, if non-zero, should be to the start of thetype_idssection.
proto_ids_size	uint	count of elements in the prototype identifiers list
proto_ids_off	uint	offset from the start of the file to the prototype identifiers list, or0ifproto_ids_size == 0(admittedly a strange edge case). The offset, if non-zero, should be to the start of theproto_idssection.
field_ids_size	uint	count of elements in the field identifiers list
field_ids_off	uint	offset from the start of the file to the field identifiers list, or0iffield_ids_size == 0. The offset, if non-zero, should be to the start of thefield_idssection.
method_ids_size	uint	count of elements in the method identifiers list
method_ids_off	uint	offset from the start of the file to the method identifiers list, or0ifmethod_ids_size == 0. The offset, if non-zero, should be to the start of themethod_idssection.
class_defs_size	uint	count of elements in the class definitions list
class_defs_off	uint	offset from the start of the file to the class definitions list, or0ifclass_defs_size == 0(admittedly a strange edge case). The offset, if non-zero, should be to the start of theclass_defssection.
data_size	uint	Size ofdatasection in bytes. Must be an even multiple of sizeof(uint).
data_off	uint	offset from the start of the file to the start of thedatasection.

map_list

appears in thedatasection

referenced fromheader_item

alignment: 4 bytes

This is a list of the entire contents of a file, in order. It contains some redundancy with respect to theheader_itembut is intended to be an easy form to use to iterate over an entire file. A given type may appear at most once in a map, but there is no restriction on what order types may appear in, other than the restrictions implied by the rest of the format (e.g., aheadersection must appear first, followed by astring_idssection, etc.). Additionally, the map entries must be ordered by initial offset and must not overlap.

Name	Format	Description
size	uint	size of the list, in entries
list	map_item[size]	elements of the list

map_itemFormat

Name	Format	Description
type	ushort	type of the items; see table below
unused	ushort	(unused)
size	uint	count of the number of items to be found at the indicated offset
offset	uint	offset from the start of the file to the items in question

Type Codes

Item Type	Constant	Value	Item Size In Bytes
header_item	TYPE_HEADER_ITEM	0x0000	0x70
string_id_item	TYPE_STRING_ID_ITEM	0x0001	0x04
type_id_item	TYPE_TYPE_ID_ITEM	0x0002	0x04
proto_id_item	TYPE_PROTO_ID_ITEM	0x0003	0x0c
field_id_item	TYPE_FIELD_ID_ITEM	0x0004	0x08
method_id_item	TYPE_METHOD_ID_ITEM	0x0005	0x08
class_def_item	TYPE_CLASS_DEF_ITEM	0x0006	0x20
map_list	TYPE_MAP_LIST	0x1000	4 + (item.size * 12)
type_list	TYPE_TYPE_LIST	0x1001	4 + (item.size * 2)
annotation_set_ref_list	TYPE_ANNOTATION_SET_REF_LIST	0x1002	4 + (item.size * 4)
annotation_set_item	TYPE_ANNOTATION_SET_ITEM	0x1003	4 + (item.size * 4)
class_data_item	TYPE_CLASS_DATA_ITEM	0x2000	implicit; must parse
code_item	TYPE_CODE_ITEM	0x2001	implicit; must parse
string_data_item	TYPE_STRING_DATA_ITEM	0x2002	implicit; must parse
debug_info_item	TYPE_DEBUG_INFO_ITEM	0x2003	implicit; must parse
annotation_item	TYPE_ANNOTATION_ITEM	0x2004	implicit; must parse
encoded_array_item	TYPE_ENCODED_ARRAY_ITEM	0x2005	implicit; must parse
annotations_directory_item	TYPE_ANNOTATIONS_DIRECTORY_ITEM	0x2006	implicit; must parse

string_id_item

appears in thestring_idssection

alignment: 4 bytes

Name	Format	Description
string_data_off	uint	offset from the start of the file to the string data for this item. The offset should be to a location in thedatasection, and the data should be in the format specified by "string_data_item" below. There is no alignment requirement for the offset.

string_data_item

appears in thedatasection

alignment: none (byte-aligned)

Name	Format	Description
utf16_size	uleb128	size of this string, in UTF-16 code units (which is the "string length" in many systems). That is, this is the decoded length of the string. (The encoded length is implied by the position of the0byte.)
data	ubyte[]	a series of MUTF-8 code units (a.k.a. octets, a.k.a. bytes) followed by a byte of value0. See "MUTF-8 (Modified UTF-8) Encoding" above for details and discussion about the data format. Note:It is acceptable to have a string which includes (the encoded form of) UTF-16 surrogate code units (that is,U+d800…U+dfff) either in isolation or out-of-order with respect to the usual encoding of Unicode into UTF-16. It is up to higher-level uses of strings to reject such invalid encodings, if appropriate.

type_id_item

appears in thetype_idssection

alignment: 4 bytes

Name	Format	Description
descriptor_idx	uint	index into thestring_idslist for the descriptor string of this type. The string must conform to the syntax forTypeDescriptor, defined above.

proto_id_item

appears in theproto_idssection

alignment: 4 bytes

Name	Format	Description
shorty_idx	uint	index into thestring_idslist for the short-form descriptor string of this prototype. The string must conform to the syntax forShortyDescriptor, defined above, and must correspond to the return type and parameters of this item.
return_type_idx	uint	index into thetype_idslist for the return type of this prototype
parameters_off	uint	offset from the start of the file to the list of parameter types for this prototype, or0if this prototype has no parameters. This offset, if non-zero, should be in thedatasection, and the data there should be in the format specified by"type_list"below. Additionally, there should be no reference to the typevoidin the list.

field_id_item

appears in thefield_idssection

alignment: 4 bytes

Name	Format	Description
class_idx	ushort	index into thetype_idslist for the definer of this field. This must be a class type, and not an array or primitive type.
type_idx	ushort	index into thetype_idslist for the type of this field
name_idx	uint	index into thestring_idslist for the name of this field. The string must conform to the syntax forMemberName, defined above.

method_id_item

appears in themethod_idssection

alignment: 4 bytes

Name	Format	Description
class_idx	ushort	index into thetype_idslist for the definer of this method. This must be a class or array type, and not a primitive type.
proto_idx	ushort	index into theproto_idslist for the prototype of this method
name_idx	uint	index into thestring_idslist for the name of this method. The string must conform to the syntax forMemberName, defined above.

class_def_item

appears in theclass_defssection

alignment: 4 bytes

Name	Format	Description
class_idx	uint	index into thetype_idslist for this class. This must be a class type, and not an array or primitive type.
access_flags	uint	access flags for the class (public,final, etc.). See "access_flagsDefinitions" for details.
superclass_idx	uint	index into thetype_idslist for the superclass, or the constant valueNO_INDEXif this class has no superclass (i.e., it is a root class such asObject). If present, this must be a class type, and not an array or primitive type.
interfaces_off	uint	offset from the start of the file to the list of interfaces, or0if there are none. This offset should be in thedatasection, and the data there should be in the format specified by "type_list" below. Each of the elements of the list must be a class type (not an array or primitive type), and there must not be any duplicates.
source_file_idx	uint	index into thestring_idslist for the name of the file containing the original source for (at least most of) this class, or the special valueNO_INDEXto represent a lack of this information. Thedebug_info_itemof any given method may override this source file, but the expectation is that most classes will only come from one source file.
annotations_off	uint	offset from the start of the file to the annotations structure for this class, or0if there are no annotations on this class. This offset, if non-zero, should be in thedatasection, and the data there should be in the format specified by "annotations_directory_item" below, with all items referring to this class as the definer.
class_data_off	uint	offset from the start of the file to the associated class data for this item, or0if there is no class data for this class. (This may be the case, for example, if this class is a marker interface.) The offset, if non-zero, should be in thedatasection, and the data there should be in the format specified by "class_data_item" below, with all items referring to this class as the definer.
static_values_off	uint	offset from the start of the file to the list of initial values forstaticfields, or0if there are none (and allstaticfields are to be initialized with0ornull). This offset should be in thedatasection, and the data there should be in the format specified by "encoded_array_item" below. The size of the array must be no larger than the number ofstaticfields declared by this class, and the elements correspond to thestaticfields in the same order as declared in the correspondingfield_list. The type of each array element must match the declared type of its corresponding field. If there are fewer elements in the array than there arestaticfields, then the leftover fields are initialized with a type-appropriate0ornull.

class_data_item

referenced fromclass_def_item

appears in thedatasection

alignment: none (byte-aligned)

Name	Format	Description
static_fields_size	uleb128	the number of static fields defined in this item
instance_fields_size	uleb128	the number of instance fields defined in this item
direct_methods_size	uleb128	the number of direct methods defined in this item
virtual_methods_size	uleb128	the number of virtual methods defined in this item
static_fields	encoded_field[static_fields_size]	the defined static fields, represented as a sequence of encoded elements. The fields must be sorted byfield_idxin increasing order.
instance_fields	encoded_field[instance_fields_size]	the defined instance fields, represented as a sequence of encoded elements. The fields must be sorted byfield_idxin increasing order.
direct_methods	encoded_method[direct_methods_size]	the defined direct (any ofstatic,private, or constructor) methods, represented as a sequence of encoded elements. The methods must be sorted bymethod_idxin increasing order.
virtual_methods	encoded_method[virtual_methods_size]	the defined virtual (none ofstatic,private, or constructor) methods, represented as a sequence of encoded elements. This list shouldnotinclude inherited methods unless overridden by the class that this item represents. The methods must be sorted bymethod_idxin increasing order.

Note:All elements'field_ids andmethod_ids must refer to the same defining class.

encoded_fieldFormat

Name	Format	Description
field_idx_diff	uleb128	index into thefield_idslist for the identity of this field (includes the name and descriptor), represented as a difference from the index of previous element in the list. The index of the first element in a list is represented directly.
access_flags	uleb128	access flags for the field (public,final, etc.). See "access_flagsDefinitions" for details.

encoded_methodFormat

Name	Format	Description
method_idx_diff	uleb128	index into themethod_idslist for the identity of this method (includes the name and descriptor), represented as a difference from the index of previous element in the list. The index of the first element in a list is represented directly.
access_flags	uleb128	access flags for the method (public,final, etc.). See "access_flagsDefinitions" for details.
code_off	uleb128	offset from the start of the file to the code structure for this method, or0if this method is eitherabstractornative. The offset should be to a location in thedatasection. The format of the data is specified by "code_item" below.

type_list

referenced fromclass_def_itemandproto_id_item

appears in thedatasection

alignment: 4 bytes

Name	Format	Description
size	uint	size of the list, in entries
list	type_item[size]	elements of the list

type_itemFormat

Name	Format	Description
type_idx	ushort	index into thetype_idslist

code_item

referenced frommethod_item

appears in thedatasection

alignment: 4 bytes

Name	Format	Description
registers_size	ushort	the number of registers used by this code
ins_size	ushort	the number of words of incoming arguments to the method that this code is for
outs_size	ushort	the number of words of outgoing argument space required by this code for method invocation
tries_size	ushort	the number oftry_items for this instance. If non-zero, then these appear as thetriesarray just after theinsnsin this instance.
debug_info_off	uint	offset from the start of the file to the debug info (line numbers + local variable info) sequence for this code, or0if there simply is no information. The offset, if non-zero, should be to a location in thedatasection. The format of the data is specified by "debug_info_item" below.
insns_size	uint	size of the instructions list, in 16-bit code units
insns	ushort[insns_size]	actual array of bytecode. The format of code in aninsnsarray is specified by the companion document"Bytecode for the Dalvik VM". Note that though this is defined as an array ofushort, there are some internal structures that prefer four-byte alignment. Also, if this happens to be in an endian-swapped file, then the swapping isonlydone on individualushorts and not on the larger internal structures.
padding	ushort(optional)= 0	two bytes of padding to maketriesfour-byte aligned. This element is only present iftries_sizeis non-zero andinsns_sizeis odd.
tries	try_item[tries_size](optional)	array indicating where in the code exceptions may be caught and how to handle them. Elements of the array must be non-overlapping in range and in order from low to high address. This element is only present iftries_sizeis non-zero.
handlers	encoded_catch_handler_list(optional)	bytes representing a list of lists of catch types and associated handler addresses. Eachtry_itemhas a byte-wise offset into this structure. This element is only present iftries_sizeis non-zero.

try_itemFormat

Name	Format	Description
start_addr	uint	start address of the block of code covered by this entry. The address is a count of 16-bit code units to the start of the first covered instruction.
insn_count	ushort	number of 16-bit code units covered by this entry. The last code unit covered (inclusive) isstart_addr + insn_count - 1.
handler_off	ushort	offset in bytes from the start of the associated encoded handler data to thecatch_handler_itemfor this entry

encoded_catch_handler_listFormat

Name	Format	Description
size	uleb128	size of this list, in entries
list	encoded_catch_handler[handlers_size]	actual list of handler lists, represented directly (not as offsets), and concatenated sequentially

encoded_catch_handlerFormat

Name	Format	Description
size	sleb128	number of catch types in this list. If non-positive, then this is the negative of the number of catch types, and the catches are followed by a catch-all handler. For example: Asizeof0means that there is a catch-all but no explicitly typed catches. Asizeof2means that there are two explicitly typed catches and no catch-all. And asizeof-1means that there is one typed catch along with a catch-all.
handlers	encoded_type_addr_pair[abs(size)]	stream ofabs(size)encoded items, one for each caught type, in the order that the types should be tested.
catch_all_addr	uleb128(optional)	bytecode address of the catch-all handler. This element is only present ifsizeis non-positive.

encoded_type_addr_pairFormat

Name	Format	Description
type_idx	uleb128	index into thetype_idslist for the type of the exception to catch
addr	uleb128	bytecode address of the associated exception handler

debug_info_item

referenced fromcode_item

appears in thedatasection

alignment: none (byte-aligned)

Eachdebug_info_itemdefines a DWARF3-inspired byte-coded state machine that, when interpreted, emits the positions table and (potentially) the local variable information for acode_item. The sequence begins with a variable-length header (the length of which depends on the number of method parameters), is followed by the state machine bytecodes, and ends with anDBG_END_SEQUENCEbyte.

The state machine consists of five registers. Theaddressregister represents the instruction offset in the associatedinsns_itemin 16-bit code units. Theaddressregister starts at0at the beginning of eachdebug_infosequence and may only monotonically increase. Thelineregister represents what source line number should be associated with the next positions table entry emitted by the state machine. It is initialized in the sequence header, and may change in positive or negative directions but must never be less than1. Thesource_fileregister represents the source file that the line number entries refer to. It is initialized to the value ofsource_file_idxinclass_def_item. The other two variables,prologue_endandepilogue_begin, are boolean flags (initialized tofalse) that indicate whether the next position emitted should be considered a method prologue or epilogue. The state machine must also track the name and type of the last local variable live in each register for theDBG_RESTART_LOCALcode.

The header is as follows:

Name	Format	Description
line_start	uleb128	the initial value for the state machine'slineregister. Does not represent an actual positions entry.
parameters_size	uleb128	the number of parameter names that are encoded. There should be one per method parameter, excluding an instance method'sthis, if any.
parameter_names	uleb128p1[parameters_size]	string index of the method parameter name. An encoded value ofNO_INDEXindicates that no name is available for the associated parameter. The type descriptor and signature are implied from the method descriptor and signature.

The byte code values are as follows:

Name	Value	Format	Arguments	Description
DBG_END_SEQUENCE	0x00		(none)	terminates a debug info sequence for acode_item
DBG_ADVANCE_PC	0x01	uleb128addr_diff	addr_diff: amount to add to address register	advances the address register without emitting a positions entry
DBG_ADVANCE_LINE	0x02	sleb128line_diff	line_diff: amount to change line register by	advances the line register without emitting a positions entry
DBG_START_LOCAL	0x03	uleb128register_num uleb128p1name_idx uleb128p1type_idx	register_num: register that will contain local name_idx: string index of the name type_idx: type index of the type	introduces a local variable at the current address. Eithername_idxortype_idxmay beNO_INDEXto indicate that that value is unknown.
DBG_START_LOCAL_EXTENDED	0x04	uleb128register_num uleb128p1name_idx uleb128p1type_idx uleb128p1sig_idx	register_num: register that will contain local name_idx: string index of the name type_idx: type index of the type sig_idx: string index of the type signature	introduces a local with a type signature at the current address. Any ofname_idx,type_idx, orsig_idxmay beNO_INDEXto indicate that that value is unknown. (Ifsig_idxis-1, though, the same data could be represented more efficiently using the opcodeDBG_START_LOCAL.) Note:See the discussion under "dalvik.annotation.Signature" below for caveats about handling signatures.
DBG_END_LOCAL	0x05	uleb128register_num	register_num: register that contained local	marks a currently-live local variable as out of scope at the current address
DBG_RESTART_LOCAL	0x06	uleb128register_num	register_num: register to restart	re-introduces a local variable at the current address. The name and type are the same as the last local that was live in the specified register.
DBG_SET_PROLOGUE_END	0x07		(none)	sets theprologue_endstate machine register, indicating that the next position entry that is added should be considered the end of a method prologue (an appropriate place for a method breakpoint). Theprologue_endregister is cleared by any special (>= 0x0a) opcode.
DBG_SET_EPILOGUE_BEGIN	0x08		(none)	sets theepilogue_beginstate machine register, indicating that the next position entry that is added should be considered the beginning of a method epilogue (an appropriate place to suspend execution before method exit). Theepilogue_beginregister is cleared by any special (>= 0x0a) opcode.
DBG_SET_FILE	0x09	uleb128p1name_idx	name_idx: string index of source file name;NO_INDEXif unknown	indicates that all subsequent line number entries make reference to this source file name, instead of the default name specified incode_item
Special Opcodes	0x0a…0xff		(none)	advances thelineandaddressregisters, emits a position entry, and clearsprologue_endandepilogue_begin. See below for description.

Special Opcodes

Opcodes with values between0x0aand0xff(inclusive) move both thelineandaddressregisters by a small amount and then emit a new position table entry. The formula for the increments are as follows:

DBG_FIRST_SPECIAL = 0x0a // the smallest special opcode

DBG_LINE_BASE = -4 // the smallest line number increment

DBG_LINE_RANGE = 15 // the number of line increments represented

adjusted_opcode = opcode - DBG_FIRST_SPECIAL

line += DBG_LINE_BASE + (adjusted_opcode % DBG_LINE_RANGE)

address += (adjusted_opcode / DBG_LINE_RANGE)

annotations_directory_item

referenced fromclass_def_item

appears in thedatasection

alignment: 4 bytes

Name	Format	Description
class_annotations_off	uint	offset from the start of the file to the annotations made directly on the class, or0if the class has no direct annotations. The offset, if non-zero, should be to a location in thedatasection. The format of the data is specified by "annotation_set_item" below.
fields_size	uint	count of fields annotated by this item
annotated_methods_off	uint	count of methods annotated by this item
annotated_parameters_off	uint	count of method parameter lists annotated by this item
field_annotations	field_annotation[fields_size](optional)	list of associated field annotations. The elements of the list must be sorted in increasing order, byfield_idx.
method_annotations	method_annotation[methods_size](optional)	list of associated method annotations. The elements of the list must be sorted in increasing order, bymethod_idx.
parameter_annotations	parameter_annotation[parameters_size](optional)	list of associated method parameter annotations. The elements of the list must be sorted in increasing order, bymethod_idx.

Note:All elements'field_ids andmethod_ids must refer to the same defining class.

field_annotationFormat

Name	Format	Description
field_idx	uint	index into thefield_idslist for the identity of the field being annotated
annotations_off	uint	offset from the start of the file to the list of annotations for the field. The offset should be to a location in thedatasection. The format of the data is specified by "annotation_set_item" below.

method_annotationFormat

Name	Format	Description
method_idx	uint	index into themethod_idslist for the identity of the method being annotated
annotations_off	uint	offset from the start of the file to the list of annotations for the method. The offset should be to a location in thedatasection. The format of the data is specified by "annotation_set_item" below.

parameter_annotationFormat

Name	Format	Description
method_idx	uint	index into themethod_idslist for the identity of the method whose parameters are being annotated
annotations_off	uint	offset from the start of the file to the list of annotations for the method parameters. The offset should be to a location in thedatasection. The format of the data is specified by "annotation_set_ref_list" below.

annotation_set_ref_list

referenced fromparameter_annotations_item

appears in thedatasection

alignment: 4 bytes

Name	Format	Description
size	uint	size of the list, in entries
list	annotation_set_ref_item[size]	elements of the list

annotation_set_ref_itemFormat

Name	Format	Description
annotations_off	uint	offset from the start of the file to the referenced annotation set or0if there are no annotations for this element. The offset, if non-zero, should be to a location in thedatasection. The format of the data is specified by "annotation_set_item" below.

annotation_set_item

referenced fromannotations_directory_item,field_annotations_item,method_annotations_item, andannotation_set_ref_item

appears in thedatasection

alignment: 4 bytes

Name	Format	Description
size	uint	size of the set, in entries
entries	annotation_off_item[size]	elements of the set. The elements must be sorted in increasing order, bytype_idx.

annotation_off_itemFormat

Name	Format	Description
annotation_off	uint	offset from the start of the file to an annotation. The offset should be to a location in thedatasection, and the format of the data at that location is specified by "annotation_item" below.

annotation_item

referenced fromannotation_set_item

appears in thedatasection

alignment: none (byte-aligned)

Name	Format	Description
visibility	ubyte	intended visibility of this annotation (see below)
annotation	encoded_annotation	encoded annotation contents, in the format described by "encoded_annotationFormat" under "encoded_valueEncoding" above.

Visibility values

These are the options for thevisibilityfield in anannotation_item:

Name	Value	Description
VISIBILITY_BUILD	0x00	intended only to be visible at build time (e.g., during compilation of other code)
VISIBILITY_RUNTIME	0x01	intended to visible at runtime
VISIBILITY_SYSTEM	0x02	intended to visible at runtime, but only to the underlying system (and not to regular user code)

encoded_array_item

referenced fromclass_def_item

appears in thedatasection

alignment: none (byte-aligned)

Name	Format	Description
value	encoded_array	bytes representing the encoded array value, in the format specified by "encoded_arrayFormat" under "encoded_valueEncoding" above.

System Annotations

System annotations are used to represent various pieces of reflective information about classes (and methods and fields). This information is generally only accessed indirectly by client (non-system) code.

System annotations are represented in.dexfiles as annotations with visibility set toVISIBILITY_SYSTEM.

dalvik.annotation.AnnotationDefault

appears on methods in annotation interfaces

AnAnnotationDefaultannotation is attached to each annotation interface which wishes to indicate default bindings.

Name	Format	Description
value	Annotation	the default bindings for this annotation, represented as an annotation of this type. The annotation need not include all names defined by the annotation; missing names simply do not have defaults.

dalvik.annotation.EnclosingClass

appears on classes

AnEnclosingClassannotation is attached to each class which is either defined as a member of another class, per se, or is anonymous but not defined within a method body (e.g., a synthetic inner class). Every class that has this annotation must also have anInnerClassannotation. Additionally, a class may not have both anEnclosingClassand anEnclosingMethodannotation.

Name	Format	Description
value	Class	the class which most closely lexically scopes this class

dalvik.annotation.EnclosingMethod

appears on classes

AnEnclosingMethodannotation is attached to each class which is defined inside a method body. Every class that has this annotation must also have anInnerClassannotation. Additionally, a class may not have both anEnclosingClassand anEnclosingMethodannotation.

Name	Format	Description
value	Method	the method which most closely lexically scopes this class

dalvik.annotation.InnerClass

appears on classes

AnInnerClassannotation is attached to each class which is defined in the lexical scope of another class's definition. Any class which has this annotation must also haveeitheranEnclosingClassannotationoranEnclosingMethodannotation.

Name	Format	Description
name	String	the originally declared simple name of this class (not including any package prefix). If this class is anonymous, then the name isnull.
accessFlags	int	the originally declared access flags of the class (which may differ from the effective flags because of a mismatch between the execution models of the source language and target virtual machine)

dalvik.annotation.MemberClasses

appears on classes

AMemberClassesannotation is attached to each class which declares member classes. (A member class is a direct inner class that has a name.)

Name	Format	Description
value	Class[]	array of the member classes

dalvik.annotation.Signature

appears on classes, fields, and methods

ASignatureannotation is attached to each class, field, or method which is defined in terms of a more complicated type than is representable by atype_id_item. The.dexformat does not define the format for signatures; it is merely meant to be able to represent whatever signatures a source language requires for successful implementation of that language's semantics. As such, signatures are not generally parsed (or verified) by virtual machine implementations. The signatures simply get handed off to higher-level APIs and tools (such as debuggers). Any use of a signature, therefore, should be written so as not to make any assumptions about only receiving valid signatures, explicitly guarding itself against the possibility of coming across a syntactically invalid signature.

Because signature strings tend to have a lot of duplicated content, aSignatureannotation is defined as anarrayof strings, where duplicated elements naturally refer to the same underlying data, and the signature is taken to be the concatenation of all the strings in the array. There are no rules about how to pull apart a signature into separate strings; that is entirely up to the tools that generate.dexfiles.

Name	Format	Description
value	String[]	the signature of this class or member, as an array of strings that is to be concatenated together

dalvik.annotation.Throws

appears on methods

AThrowsannotation is attached to each method which is declared to throw one or more exception types.

Name	Format	Description
value	Class[]	the array of exception types thrown