Android Dex文件结构

dex — Dalvik Executable Format

This document describes the layout and contents of .dex files, 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 plus 1, variable-length (see below)

LEB128

LEB128 ("Little-Endian Base 128") is a variable-length encoding for arbitrary signed or unsigned integer quantities. The format was borrowed from the DWARF3 specification. In a .dex file, 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 as 0.

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 variant uleb128p1 is used to represent a signed value, where the representation is of the valueplus one encoded as a uleb128. This makes the encoding of -1 (alternatively thought of as the unsigned value 0xffffffff) — 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 (or 0xffffffff), 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	As sleb128	As uleb128	As uleb128p1
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 by string_id index.
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 (by type_id index) major order, and then by arguments (also bytype_id index).
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 (by type_id index) is the major order, field name (bystring_id index) is the intermediate order, and type (by type_id index) 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 (by type_id index) is the major order, method name (by string_id index) is the intermediate order, and method prototype (by proto_id index) 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 in header_item

The constant array/string DEX_FILE_MAGIC is 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" or 0x0a) and a null byte ("/0" or 0x00) 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, version 009 was used for the M3 releases of the Android platform (November-December 2007), and version 013 was 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_CONSTANT and REVERSE_ENDIAN_CONSTANT

embedded in header_item

The constant ENDIAN_CONSTANT is used to indicate the endianness of the file in which it is found. Although the standard .dex format is little-endian, implementations may choose to perform byte-swapping. Should an implementation come across a header whose endian_tag is REVERSE_ENDIAN_CONSTANT instead 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 in class_def_item and debug_info_item

The constant NO_INDEX is used to indicate that an index value is absent.

Note: This value isn't defined to be 0, because that is in fact typically a valid index.

Also Note: The chosen value for NO_INDEX is representable as a single byte in the uleb128p1 encoding.

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

access_flags Definitions

embedded in class_def_item, field_item, method_item, and InnerClass

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 outerthis reference	static: global to defining class	static: does not take a this argument
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 when ACC_NATIVE is 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			declared synchronized. Note: This has no effect on execution (other than in reflection of this flag, per se).

* Only allowed on for InnerClass annotations, and must not ever be on in a class_def_item.

MUTF-8 (Modified UTF-8) Encoding

As a concession to easier legacy support, the .dex format 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 range U+10000 … U+10ffff are encoded as a surrogate pair, each of which is represented as a three-byte encoded value.
The code point U+0000 is encoded in two-byte form.
A plain null byte (value 0) 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 point U+0000 in a stringand still manipulate it as a C-style null-terminated string.

However, the special encoding of U+0000 means that, unlike normal UTF-8, the result of calling the standard C function strcmp() on a pair of MUTF-8 strings does not always indicate the properly signed result of comparison of unequal strings. 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 to The Unicode Standard for further information about character encoding. MUTF-8 is actually closer to the (relatively less well-known) encoding CESU-8 than to UTF-8 per se.

encoded_value Encoding

embedded in annotation_element and encoded_array_item

An encoded_value is 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 subsequent value along with an optional clarifying argument in the high-order three bits. See below for the various value definitions. In most cases, value_arg encodes the length of the immediately-subsequent value in bytes, as (size - 1), e.g., 0 means that the value requires one byte, and 7 means it requires eight bytes; however, there are exceptions as noted below.
value	ubyte[]	bytes representing the value, variable in length and interpreted differently for different value_type bytes, though always little-endian. See the various value definitions below for details.

Value Formats

Type Name	value_type	value_argFormat	value Format	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-extended to 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 the string_ids section 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 the type_ids section 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 the field_ids section 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 the method_ids section 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 the field_ids section 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_array Format" below. The size of the value is 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 the valueis implicit in the encoding.
VALUE_NULL	0x1e	(none; must be0)	(none)	null reference value
VALUE_BOOLEAN	0x1f	boolean (0…1)	(none)	one-bit value; 0 for false and 1 fortrue. The bit is represented in thevalue_arg.

encoded_array Format

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

encoded_annotation Format

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 by string_idindex.

annotation_element Format

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

String Syntax

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

SimpleName

A SimpleName is the basis for the syntax of the names of other things. The .dex format 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 range U+d800 … U+dfff) are not considered valid name characters, per se, but Unicode supplemental characters are valid (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 by field_id_item and method_id_item

A MemberName is the name of a member of a class, members being fields, methods, and inner classes.

MemberName →
	SimpleName
\|	'<' SimpleName '>'

FullClassName

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

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

TypeDescriptor

used by type_id_item

A TypeDescriptor is the representation of any type, including primitives, classes, arrays, and void. 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 by proto_id_item

A ShortyDescriptor is 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'

TypeDescriptor Semantics

This is the meaning of each of the variants of TypeDescriptor.

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 class fully.qualified.Name
[descriptor	array of descriptor, 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 .dex file.

header_item

appears in the header section

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 but magicand 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_CONSTANTand REVERSE_ENDIAN_CONSTANT" for more details.
link_size	uint	size of the link section, or 0 if this file isn't statically linked
link_off	uint	offset from the start of the file to the link section, or 0 iflink_size == 0. The offset, if non-zero, should be to an offset into the link_data section. 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, or 0 if this file has no map. The offset, if non-zero, should be to an offset into the data section, 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, or 0 ifstring_ids_size == 0 (admittedly a strange edge case). The offset, if non-zero, should be to the start of the string_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, or 0 iftype_ids_size == 0 (admittedly a strange edge case). The offset, if non-zero, should be to the start of the type_ids section.
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, or 0 if proto_ids_size == 0 (admittedly a strange edge case). The offset, if non-zero, should be to the start of the proto_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, or 0 iffield_ids_size == 0. The offset, if non-zero, should be to the start of the field_ids section.
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, or 0if method_ids_size == 0. The offset, if non-zero, should be to the start of the method_ids section.
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, or 0 ifclass_defs_size == 0 (admittedly a strange edge case). The offset, if non-zero, should be to the start of the class_defssection.
data_size	uint	Size of data section in bytes. Must be an even multiple of sizeof(uint).
data_off	uint	offset from the start of the file to the start of the data section.

map_list

appears in the data section

referenced from header_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_item but 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., a header section must appear first, followed by a string_ids section, 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_item Format

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 the string_ids section

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 the data section, 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 the data section

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 the 0 byte.)
data	ubyte[]	a series of MUTF-8 code units (a.k.a. octets, a.k.a. bytes) followed by a byte of value 0. 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.

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 the 0 byte.)

data

ubyte[]

a series of MUTF-8 code units (a.k.a. octets, a.k.a. bytes) followed by a byte of value 0. 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 the type_ids section

alignment: 4 bytes

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

proto_id_item

appears in the proto_ids section

alignment: 4 bytes

Name	Format	Description
shorty_idx	uint	index into the string_ids list for the short-form descriptor string of this prototype. The string must conform to the syntax for ShortyDescriptor, defined above, and must correspond to the return type and parameters of this item.
return_type_idx	uint	index into the type_ids list 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, or 0 if this prototype has no parameters. This offset, if non-zero, should be in the data section, and the data there should be in the format specified by "type_list" below. Additionally, there should be no reference to the type void in the list.

field_id_item

appears in the field_ids section

alignment: 4 bytes

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

method_id_item

appears in the method_ids section

alignment: 4 bytes

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

class_def_item

appears in the class_defs section

alignment: 4 bytes

Name	Format	Description
class_idx	uint	index into the type_ids list 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_flags Definitions" for details.
superclass_idx	uint	index into the type_ids list for the superclass, or the constant value NO_INDEXif this class has no superclass (i.e., it is a root class such as Object). 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, or 0 if there are none. This offset should be in the data section, 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 the string_ids list for the name of the file containing the original source for (at least most of) this class, or the special value NO_INDEX to represent a lack of this information. The debug_info_item of 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, or0 if there are no annotations on this class. This offset, if non-zero, should be in the data section, 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, or0 if 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 thedata section, 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 for static fields, or0 if there are none (and all static fields are to be initialized with 0 or null). This offset should be in the data section, 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 of static fields declared by this class, and the elements correspond to the static fields in the same order as declared in the corresponding field_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 are static fields, then the leftover fields are initialized with a type-appropriate 0 or null.

class_data_item

referenced from class_def_item

appears in the data section

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 by field_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 by field_idx in increasing order.
direct_methods	encoded_method[direct_methods_size]	the defined direct (any of static,private, or constructor) methods, represented as a sequence of encoded elements. The methods must be sorted by method_idx in increasing order.
virtual_methods	encoded_method[virtual_methods_size]	the defined virtual (none of static,private, or constructor) methods, represented as a sequence of encoded elements. This list should notinclude inherited methods unless overridden by the class that this item represents. The methods must be sorted by method_idx in increasing order.

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

encoded_field Format

Name	Format	Description
field_idx_diff	uleb128	index into the field_ids list 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_flags Definitions" for details.

encoded_method Format

Name	Format	Description
method_idx_diff	uleb128	index into the method_ids list 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, or 0 if this method is either abstract or native. The offset should be to a location in the data section. The format of the data is specified by "code_item" below.

type_list

referenced from class_def_item and proto_id_item

appears in the data section

alignment: 4 bytes

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

type_item Format

Name	Format	Description
type_idx	ushort	index into the type_ids list

code_item

referenced from method_item

appears in the data section

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 of try_items for this instance. If non-zero, then these appear as the tries array just after the insnsin 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, or0 if there simply is no information. The offset, if non-zero, should be to a location in the data section. 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 an insnsarray is specified by the companion document "Bytecode for the Dalvik VM". Note that though this is defined as an array of ushort, there are some internal structures that prefer four-byte alignment. Also, if this happens to be in an endian-swapped file, then the swapping is only done on individual ushorts and not on the larger internal structures.
padding	ushort (optional) = 0	two bytes of padding to make tries four-byte aligned. This element is only present if tries_size is non-zero andinsns_size is 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 if tries_sizeis non-zero.
handlers	encoded_catch_handler_list(optional)	bytes representing a list of lists of catch types and associated handler addresses. Each try_item has a byte-wise offset into this structure. This element is only present if tries_size is non-zero.

try_item Format

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) is start_addr + insn_count - 1.
handler_off	ushort	offset in bytes from the start of the associated encoded handler data to thecatch_handler_item for this entry

encoded_catch_handler_list Format

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_handler Format

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: A size of 0 means that there is a catch-all but no explicitly typed catches. A size of 2 means that there are two explicitly typed catches and no catch-all. And a size of -1means that there is one typed catch along with a catch-all.
handlers	encoded_type_addr_pair[abs(size)]	stream of abs(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 if size is non-positive.

encoded_type_addr_pair Format

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

debug_info_item

referenced from code_item

appears in the data section

alignment: none (byte-aligned)

Each debug_info_item defines a DWARF3-inspired byte-coded state machine that, when interpreted, emits the positions table and (potentially) the local variable information for a code_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 an DBG_END_SEQUENCE byte.

The state machine consists of five registers. The address register represents the instruction offset in the associated insns_item in 16-bit code units. The address register starts at 0 at the beginning of eachdebug_info sequence and may only monotonically increase. The line register 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 than 1. The source_file register represents the source file that the line number entries refer to. It is initialized to the value of source_file_idx in class_def_item. The other two variables, prologue_end andepilogue_begin, are boolean flags (initialized to false) 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 the DBG_RESTART_LOCAL code.

The header is as follows:

Name	Format	Description
line_start	uleb128	the initial value for the state machine's line register. 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's this, if any.
parameter_names	uleb128p1[parameters_size]	string index of the method parameter name. An encoded value of NO_INDEX indicates 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 a code_item
DBG_ADVANCE_PC	0x01	uleb128 addr_diff	addr_diff: amount to add to address register	advances the address register without emitting a positions entry
DBG_ADVANCE_LINE	0x02	sleb128 line_diff	line_diff: amount to change line register by	advances the line register without emitting a positions entry
DBG_START_LOCAL	0x03	uleb128 register_num uleb128p1 name_idx uleb128p1 type_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. Either name_idx or type_idxmay be NO_INDEX to indicate that that value is unknown.
DBG_START_LOCAL_EXTENDED	0x04	uleb128 register_num uleb128p1 name_idx uleb128p1 type_idx uleb128p1 sig_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, or sig_idxmay be NO_INDEX to indicate that that value is unknown. (If sig_idx is -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	uleb128 register_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	uleb128 register_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 the prologue_end state 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_end register is cleared by any special (>= 0x0a) opcode.
DBG_SET_EPILOGUE_BEGIN	0x08		(none)	sets the epilogue_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_begin register is cleared by any special (>= 0x0a) opcode.
DBG_SET_FILE	0x09	uleb128p1 name_idx	name_idx: string index of source file name;NO_INDEX if unknown	indicates that all subsequent line number entries make reference to this source file name, instead of the default name specified in code_item
Special Opcodes	0x0a…0xff		(none)	advances the line andaddress registers, emits a position entry, and clearsprologue_end andepilogue_begin. See below for description.

Special Opcodes

Opcodes with values between 0x0a and 0xff (inclusive) move both the line and address registers 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 from class_def_item

appears in the data section

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, or 0 if the class has no direct annotations. The offset, if non-zero, should be to a location in the datasection. 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, by field_idx.
method_annotations	method_annotation[methods_size](optional)	list of associated method annotations. The elements of the list must be sorted in increasing order, by method_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 and method_ids must refer to the same defining class.

field_annotation Format

Name	Format	Description
field_idx	uint	index into the field_ids list 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 the data section. The format of the data is specified by "annotation_set_item" below.

method_annotation Format

Name	Format	Description
method_idx	uint	index into the method_ids list 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 the data section. The format of the data is specified by "annotation_set_item" below.

parameter_annotation Format

Name	Format	Description
method_idx	uint	index into the method_ids list 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 the data section. The format of the data is specified by "annotation_set_ref_list" below.

annotation_set_ref_list

referenced from parameter_annotations_item

appears in the data section

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_item Format

Name	Format	Description
annotations_off	uint	offset from the start of the file to the referenced annotation set or 0 if there are no annotations for this element. The offset, if non-zero, should be to a location in the data section. The format of the data is specified by "annotation_set_item" below.

annotation_set_item

referenced from annotations_directory_item, field_annotations_item, method_annotations_item, and annotation_set_ref_item

appears in the data section

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, by type_idx.

annotation_off_item Format

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

annotation_item

referenced from annotation_set_item

appears in the data section

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_annotation Format" under "encoded_value Encoding" above.

Visibility values

These are the options for the visibility field in an annotation_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 from class_def_item

appears in the data section

alignment: none (byte-aligned)

Name	Format	Description
value	encoded_array	bytes representing the encoded array value, in the format specified by "encoded_array Format" under "encoded_value Encoding" 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 .dex files as annotations with visibility set to VISIBILITY_SYSTEM.

dalvik.annotation.AnnotationDefault

appears on methods in annotation interfaces

An AnnotationDefault annotation 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

An EnclosingClass annotation 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 an InnerClass annotation. Additionally, a class may not have both an EnclosingClass and an EnclosingMethod annotation.

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

dalvik.annotation.EnclosingMethod

appears on classes

An EnclosingMethod annotation is attached to each class which is defined inside a method body. Every class that has this annotation must also have an InnerClass annotation. Additionally, a class may not have both an EnclosingClass and an EnclosingMethod annotation.

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

dalvik.annotation.InnerClass

appears on classes

An InnerClass annotation 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 have either an EnclosingClassannotation or an EnclosingMethod annotation.

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 is null.
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

A MemberClasses annotation 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

A Signature annotation is attached to each class, field, or method which is defined in terms of a more complicated type than is representable by a type_id_item. The .dex format 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, a Signature annotation is defined as an array of 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 .dex files.

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

A Throws annotation 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

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