Dalvik Executable Format

 

.dex — Dalvik Executable Format

Copyright © 2007 The Android Open Source Project

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

NameDescriptionbyte8-bit signed intubyte8-bit unsigned intshort16-bit signed int, little-endianushort16-bit unsigned int, little-endianint32-bit signed int, little-endianuint32-bit unsigned int, little-endianlong64-bit signed int, little-endianulong64-bit unsigned int, little-endiansleb128signed LEB128, variable-length (see below)uleb128unsigned LEB128, variable-length (see below)uleb128p1unsigned LEB128 plus 1, variable-length (see below)

LEB128

LEB128 ("Little-Endian Base128") is a variable-length encoding for arbitrary signed or unsigned integer quantities. The format was borrowed from theDWARF3 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 as0.

Bitwise diagram of a two-byte LEB128 valueFirst byteSecond byte1bit₆bit₅bit₄bit₃bit₂bit₁bit₀0bit₁₃bit₁₂bit₁₁bit₁₀bit₉bit₈bit₇

The variant uleb128p1 is used to represent a signed value, where the representation is of the valueplus one encoded 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 SequenceAs sleb128As uleb128As uleb128p10000-1011107f-112712680 7f-1281625616255

Overall File Layout

NameFormatDescriptionheaderheader_itemthe headerstring_idsstring_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_idstype_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_id index.proto_idsproto_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_id index) major order, and then by arguments (also bytype_id index).field_idsfield_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_id index) is the major order, field name (bystring_id index) is the intermediate order, and type (bytype_id index) is the minor order.method_idsmethod_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_id index) is the major order, method name (bystring_id index) is the intermediate order, and method prototype (byproto_id index) is the minor order.class_defsclass_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.dataubyte[]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_dataubyte[]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.dex file in order for it to be recognized as such. The value intentionally contains a newline ("\n" or0x0a) 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, version009 was used for the M3 releases of the Android platform (November-December 2007), and version013 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 whoseendian_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 theuleb128p1 encoding.

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

access_flags Definitions

embedded in class_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.

NameValueFor Classes (and InnerClass annotations)For FieldsFor MethodsACC_PUBLIC0x1public: visible everywherepublic: visible everywherepublic: visible everywhereACC_PRIVATE0x2* private: only visible to defining classprivate: only visible to defining classprivate: only visible to defining classACC_PROTECTED0x4* protected: visible to package and subclassesprotected: visible to package and subclassesprotected: visible to package and subclassesACC_STATIC0x8* static: is not constructed with an outer this referencestatic: global to defining classstatic: does not take a this argumentACC_FINAL0x10final: not subclassablefinal: immutable after constructionfinal: not overridableACC_SYNCHRONIZED0x20  synchronized: associated lock automatically acquired around call to this method.Note: This is only valid to set whenACC_NATIVE is also set.ACC_VOLATILE0x40 volatile: special access rules to help with thread safety ACC_BRIDGE0x40  bridge method, added automatically by compiler as a type-safe bridgeACC_TRANSIENT0x80 transient: not to be saved by default serialization ACC_VARARGS0x80  last argument should be treated as a "rest" argument by compilerACC_NATIVE0x100  native: implemented in native codeACC_INTERFACE0x200interface: multiply-implementable abstract class  ACC_ABSTRACT0x400abstract: not directly instantiable abstract: unimplemented by this classACC_STRICT0x800  strictfp: strict rules for floating-point arithmeticACC_SYNTHETIC0x1000not directly defined in source codenot directly defined in source codenot directly defined in source codeACC_ANNOTATION0x2000declared as an annotation class  ACC_ENUM0x4000declared as an enumerated typedeclared as an enumerated value (unused)0x8000   ACC_CONSTRUCTOR0x10000  constructor method (class or instance initializer)ACC_DECLARED_
SYNCHRONIZED0x20000  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 aclass_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 pointU+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 functionstrcmp() on a pair of MUTF-8 strings does not always indicate the properly signed result of comparison ofunequal 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) encodingCESU-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.

NameFormatDescription(value_arg << 5) | value_typeubytebyte indicating the type of the immediately subsequent value along with an optional clarifying argument in the high-order three bits. See below for the variousvalue definitions. In most cases,value_arg encodes the length of the immediately-subsequentvalue in bytes, as(size - 1), e.g.,0 means that the value requires one byte, and7 means it requires eight bytes; however, there are exceptions as noted below.valueubyte[]bytes representing the value, variable in length and interpreted differently for differentvalue_type bytes, though always little-endian. See the various value definitions below for details.

Value Formats

Type Namevalue_typevalue_arg Formatvalue FormatDescriptionVALUE_BYTE0x00(none; must be 0)ubyte[1]signed one-byte integer valueVALUE_SHORT0x02size - 1 (0…1)ubyte[size]signed two-byte integer value, sign-extendedVALUE_CHAR0x03size - 1 (0…1)ubyte[size]unsigned two-byte integer value, zero-extendedVALUE_INT0x04size - 1 (0…3)ubyte[size]signed four-byte integer value, sign-extendedVALUE_LONG0x06size - 1 (0…7)ubyte[size]signed eight-byte integer value, sign-extendedVALUE_FLOAT0x10size - 1 (0…3)ubyte[size]four-byte bit pattern, zero-extended to the right, and interpreted as an IEEE754 32-bit floating point valueVALUE_DOUBLE0x11size - 1 (0…7)ubyte[size]eight-byte bit pattern, zero-extended to the right, and interpreted as an IEEE754 64-bit floating point valueVALUE_STRING0x17size - 1 (0…3)ubyte[size]unsigned (zero-extended) four-byte integer value, interpreted as an index into thestring_ids section and representing a string valueVALUE_TYPE0x18size - 1 (0…3)ubyte[size]unsigned (zero-extended) four-byte integer value, interpreted as an index into thetype_ids section and representing a reflective type/class valueVALUE_FIELD0x19size - 1 (0…3)ubyte[size]unsigned (zero-extended) four-byte integer value, interpreted as an index into thefield_ids section and representing a reflective field valueVALUE_METHOD0x1asize - 1 (0…3)ubyte[size]unsigned (zero-extended) four-byte integer value, interpreted as an index into themethod_ids section and representing a reflective method valueVALUE_ENUM0x1bsize - 1 (0…3)ubyte[size]unsigned (zero-extended) four-byte integer value, interpreted as an index into thefield_ids section and representing the value of an enumerated type constantVALUE_ARRAY0x1c(none; must be 0)encoded_arrayan array of values, in the format specified by "encoded_array Format" below. The size of thevalue is implicit in the encoding.VALUE_ANNOTATION0x1d(none; must be 0)encoded_annotationa sub-annotation, in the format specified by "encoded_annotation Format" below. The size of thevalue is implicit in the encoding.VALUE_NULL0x1e(none; must be 0)(none)null reference valueVALUE_BOOLEAN0x1fboolean (0…1)(none)one-bit value; 0 for false and 1 for true. The bit is represented in the value_arg.

encoded_array Format

NameFormatDescriptionsizeuleb128number of elements in the arrayvaluesencoded_value[size]a series of size encoded_value byte sequences in the format specified by this section, concatenated sequentially.

encoded_annotation Format

NameFormatDescriptiontype_idxuleb128type of the annotation. This must be a class (not array or primitive) type.sizeuleb128number of name-value mappings in this annotationelementsannotation_element[size]elements of the annotataion, represented directly in-line (not as offsets). Elements must be sorted in increasing order bystring_id index.

annotation_element Format

NameFormatDescriptionname_idxuleb128element name, represented as an index into the string_ids section. The string must conform to the syntax forMemberName, defined above.valueencoded_valueelement 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 rangeU+d800 …U+dfff) are not considered valid name characters, per se, but Unicode supplemental charactersare 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 SimpleNameOptionalPackagePrefix → (SimpleName '/')*

TypeDescriptor

used by type_id_item

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

TypeDescriptor → 'V'|FieldTypeDescriptorFieldTypeDescriptor → NonArrayFieldTypeDescriptor|('[' * 1…255) NonArrayFieldTypeDescriptorNonArrayFieldTypeDescriptor→ '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'|ShortyFieldTypeShortyFieldType → 'Z'|'B'|'S'|'C'|'I'|'J'|'F'|'D'|'L'

TypeDescriptor Semantics

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

SyntaxMeaningVvoid; only valid for return typesZbooleanBbyteSshortCcharIintJlongFfloatDdoubleLfully/qualified/Name;the class fully.qualified.Name[descriptorarray 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

NameFormatDescriptionmagicubyte[8] = DEX_FILE_MAGICmagic value. See discussion above under "DEX_FILE_MAGIC" for more details.checksumuintadler32 checksum of the rest of the file (everything but magic and this field); used to detect file corruptionsignatureubyte[20]SHA-1 signature (hash) of the rest of the file (everything but magic,checksum, and this field); used to uniquely identify filesfile_sizeuintsize of the entire file (including the header), in bytesheader_sizeuint = 0x70size 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_taguint = ENDIAN_CONSTANTendianness tag. See discussion above under "ENDIAN_CONSTANT and REVERSE_ENDIAN_CONSTANT" for more details.link_sizeuintsize of the link section, or 0 if this file isn't statically linkedlink_offuintoffset from the start of the file to the link section, or 0 if link_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_offuintoffset 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 thedata section, and the data should be in the format specified by "map_list" below.string_ids_sizeuintcount of strings in the string identifiers liststring_ids_offuintoffset 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 thestring_ids section.type_ids_sizeuintcount of elements in the type identifiers listtype_ids_offuintoffset 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 thetype_ids section.proto_ids_sizeuintcount of elements in the prototype identifiers listproto_ids_offuintoffset 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 theproto_ids section.field_ids_sizeuintcount of elements in the field identifiers listfield_ids_offuintoffset 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 thefield_ids section.method_ids_sizeuintcount of elements in the method identifiers listmethod_ids_offuintoffset from the start of the file to the method identifiers list, or 0 ifmethod_ids_size == 0. The offset, if non-zero, should be to the start of themethod_ids section.class_defs_sizeuintcount of elements in the class definitions listclass_defs_offuintoffset 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 theclass_defs section.data_sizeuintSize of data section in bytes. Must be an even multiple of sizeof(uint).data_offuintoffset 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., aheader section must appear first, followed by astring_ids section, etc.). Additionally, the map entries must be ordered by initial offset and must not overlap.

NameFormatDescriptionsizeuintsize of the list, in entrieslistmap_item[size]elements of the list

map_item Format

NameFormatDescriptiontypeushorttype of the items; see table belowunusedushort(unused)sizeuintcount of the number of items to be found at the indicated offsetoffsetuintoffset from the start of the file to the items in question

Type Codes

Item TypeConstantValueItem Size In Bytesheader_itemTYPE_HEADER_ITEM0x00000x70string_id_itemTYPE_STRING_ID_ITEM0x00010x04type_id_itemTYPE_TYPE_ID_ITEM0x00020x04proto_id_itemTYPE_PROTO_ID_ITEM0x00030x0cfield_id_itemTYPE_FIELD_ID_ITEM0x00040x08method_id_itemTYPE_METHOD_ID_ITEM0x00050x08class_def_itemTYPE_CLASS_DEF_ITEM0x00060x20map_listTYPE_MAP_LIST0x10004 + (item.size * 12)type_listTYPE_TYPE_LIST0x10014 + (item.size * 2)annotation_set_ref_listTYPE_ANNOTATION_SET_REF_LIST0x10024 + (item.size * 4)annotation_set_itemTYPE_ANNOTATION_SET_ITEM0x10034 + (item.size * 4)class_data_itemTYPE_CLASS_DATA_ITEM0x2000implicit; must parsecode_itemTYPE_CODE_ITEM0x2001implicit; must parsestring_data_itemTYPE_STRING_DATA_ITEM0x2002implicit; must parsedebug_info_itemTYPE_DEBUG_INFO_ITEM0x2003implicit; must parseannotation_itemTYPE_ANNOTATION_ITEM0x2004implicit; must parseencoded_array_itemTYPE_ENCODED_ARRAY_ITEM0x2005implicit; must parseannotations_directory_itemTYPE_ANNOTATIONS_DIRECTORY_ITEM0x2006implicit; must parse

string_id_item

appears in the string_ids section

alignment: 4 bytes

NameFormatDescriptionstring_data_offuintoffset from the start of the file to the string data for this item. The offset should be to a location in thedata 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)

NameFormatDescriptionutf16_sizeuleb128size 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 the0 byte.)dataubyte[]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 the type_ids section

alignment: 4 bytes

NameFormatDescriptiondescriptor_idxuintindex into the string_ids list for the descriptor string of this type. The string must conform to the syntax forTypeDescriptor, defined above.

proto_id_item

appears in the proto_ids section

alignment: 4 bytes

NameFormatDescriptionshorty_idxuintindex into the string_ids list 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_idxuintindex into the type_ids list for the return type of this prototypeparameters_offuintoffset from the start of the file to the list of parameter types for this prototype, or0 if this prototype has no parameters. This offset, if non-zero, should be in thedata section, and the data there should be in the format specified by"type_list" below. Additionally, there should be no reference to the typevoid in the list.

field_id_item

appears in the field_ids section

alignment: 4 bytes

NameFormatDescriptionclass_idxushortindex 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_idxushortindex into the type_ids list for the type of this fieldname_idxuintindex into the string_ids list for the name of this field. The string must conform to the syntax forMemberName, defined above.

method_id_item

appears in the method_ids section

alignment: 4 bytes

NameFormatDescriptionclass_idxushortindex 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_idxushortindex into the proto_ids list for the prototype of this methodname_idxuintindex into the string_ids list for the name of this method. The string must conform to the syntax forMemberName, defined above.

class_def_item

appears in the class_defs section

alignment: 4 bytes

NameFormatDescriptionclass_idxuintindex into the type_ids list for this class. This must be a class type, and not an array or primitive type.access_flagsuintaccess flags for the class (public, final, etc.). See "access_flags Definitions" for details.superclass_idxuintindex into the type_ids list for the superclass, or the constant valueNO_INDEX if 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_offuintoffset from the start of the file to the list of interfaces, or 0 if there are none. This offset should be in thedata 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_idxuintindex 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 valueNO_INDEX to represent a lack of this information. Thedebug_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_offuintoffset 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 thedata 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_offuintoffset 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_offuintoffset from the start of the file to the list of initial values for static fields, or0 if there are none (and allstatic fields are to be initialized with0 ornull). This offset should be in thedata 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 ofstatic fields declared by this class, and the elements correspond to thestatic fields 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 arestatic fields, then the leftover fields are initialized with a type-appropriate0 ornull.

class_data_item

referenced from class_def_item

appears in the data section

alignment: none (byte-aligned)

NameFormatDescriptionstatic_fields_sizeuleb128the number of static fields defined in this iteminstance_fields_sizeuleb128the number of instance fields defined in this itemdirect_methods_sizeuleb128the number of direct methods defined in this itemvirtual_methods_sizeuleb128the number of virtual methods defined in this itemstatic_fieldsencoded_field[static_fields_size]the defined static fields, represented as a sequence of encoded elements. The fields must be sorted byfield_idx in increasing order.instance_fieldsencoded_field[instance_fields_size]the defined instance fields, represented as a sequence of encoded elements. The fields must be sorted byfield_idx in increasing order.direct_methodsencoded_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 bymethod_idx in increasing order.virtual_methodsencoded_method[virtual_methods_size]the defined virtual (none of static, private, or constructor) methods, represented as a sequence of encoded elements. This list shouldnot include inherited methods unless overridden by the class that this item represents. The methods must be sorted bymethod_idx in increasing order.

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

encoded_field Format

NameFormatDescriptionfield_idx_diffuleb128index 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_flagsuleb128access flags for the field (public, final, etc.). See "access_flags Definitions" for details.

encoded_method Format

NameFormatDescriptionmethod_idx_diffuleb128index 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_flagsuleb128access flags for the method (public, final, etc.). See "access_flags Definitions" for details.code_offuleb128offset 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 thedata 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

NameFormatDescriptionsizeuintsize of the list, in entrieslisttype_item[size]elements of the list

type_item Format

NameFormatDescriptiontype_idxushortindex into the type_ids list

code_item

referenced from method_item

appears in the data section

alignment: 4 bytes

NameFormatDescriptionregisters_sizeushortthe number of registers used by this codeins_sizeushortthe number of words of incoming arguments to the method that this code is forouts_sizeushortthe number of words of outgoing argument space required by this code for method invocationtries_sizeushortthe number of try_items for this instance. If non-zero, then these appear as thetries array just after theinsns in this instance.debug_info_offuintoffset 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 thedata section. The format of the data is specified by "debug_info_item" below.insns_sizeuintsize of the instructions list, in 16-bit code unitsinsnsushort[insns_size]actual array of bytecode. The format of code in an insns array 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 isonly done on individualushorts and not on the larger internal structures.paddingushort (optional) = 0two bytes of padding to make tries four-byte aligned. This element is only present iftries_size is non-zero andinsns_size is odd.triestry_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_size is non-zero.handlersencoded_catch_handler_list (optional)bytes representing a list of lists of catch types and associated handler addresses. Eachtry_item has a byte-wise offset into this structure. This element is only present iftries_size is non-zero.

try_item Format

NameFormatDescriptionstart_addruintstart 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_countushortnumber of 16-bit code units covered by this entry. The last code unit covered (inclusive) isstart_addr + insn_count - 1.handler_offushortoffset in bytes from the start of the associated encoded handler data to the catch_handler_item for this entry

encoded_catch_handler_list Format

NameFormatDescriptionsizeuleb128size of this list, in entrieslistencoded_catch_handler[handlers_size]actual list of handler lists, represented directly (not as offsets), and concatenated sequentially

encoded_catch_handler Format

NameFormatDescriptionsizesleb128number 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: Asize of0 means that there is a catch-all but no explicitly typed catches. Asize of2 means that there are two explicitly typed catches and no catch-all. And asize of-1 means that there is one typed catch along with a catch-all.handlersencoded_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_addruleb128 (optional)bytecode address of the catch-all handler. This element is only present if size is non-positive.

encoded_type_addr_pair Format

NameFormatDescriptiontype_idxuleb128index into the type_ids list for the type of the exception to catchaddruleb128bytecode 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 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_SEQUENCE byte.

The state machine consists of five registers. The address register represents the instruction offset in the associatedinsns_item in 16-bit code units. Theaddress register starts at0 at the beginning of each debug_info sequence and may only monotonically increase. Theline 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 than1. Thesource_file register represents the source file that the line number entries refer to. It is initialized to the value ofsource_file_idx inclass_def_item. The other two variables,prologue_end andepilogue_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_LOCAL code.

The header is as follows:

NameFormatDescriptionline_startuleb128the initial value for the state machine's line register. Does not represent an actual positions entry.parameters_sizeuleb128the number of parameter names that are encoded. There should be one per method parameter, excluding an instance method'sthis, if any.parameter_namesuleb128p1[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:

NameValueFormatArgumentsDescriptionDBG_END_SEQUENCE0x00 (none)terminates a debug info sequence for a code_itemDBG_ADVANCE_PC0x01uleb128 addr_diffaddr_diff: amount to add to address registeradvances the address register without emitting a positions entryDBG_ADVANCE_LINE0x02sleb128 line_diffline_diff: amount to change line register byadvances the line register without emitting a positions entryDBG_START_LOCAL0x03uleb128 register_num
uleb128p1 name_idx
uleb128p1 type_idxregister_num: register that will contain local
name_idx: string index of the name
type_idx: type index of the typeintroduces a local variable at the current address. Either name_idx ortype_idx may beNO_INDEX to indicate that that value is unknown.DBG_START_LOCAL_EXTENDED0x04uleb128 register_num
uleb128p1 name_idx
uleb128p1 type_idx
uleb128p1 sig_idxregister_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 signatureintroduces a local with a type signature at the current address. Any of name_idx, type_idx, or sig_idx may be NO_INDEX to indicate that that value is unknown. (Ifsig_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_LOCAL0x05uleb128 register_numregister_num: register that contained localmarks a currently-live local variable as out of scope at the current addressDBG_RESTART_LOCAL0x06uleb128 register_numregister_num: register to restartre-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_END0x07 (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_BEGIN0x08 (none)sets the epilogue_begin state 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_FILE0x09uleb128p1 name_idxname_idx: string index of source file name; NO_INDEX if unknownindicates that all subsequent line number entries make reference to this source file name, instead of the default name specified incode_itemSpecial Opcodes0x0a…0xff (none)advances the line and address 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 theline andaddress 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 opcodeDBG_LINE_BASE   = -4      // the smallest line number incrementDBG_LINE_RANGE  = 15      // the number of line increments representedadjusted_opcode = opcode - DBG_FIRST_SPECIALline += 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

NameFormatDescriptionclass_annotations_offuintoffset from the start of the file to the annotations made directly on the class, or0 if the class has no direct annotations. The offset, if non-zero, should be to a location in thedata section. The format of the data is specified by "annotation_set_item" below.fields_sizeuintcount of fields annotated by this itemannotated_methods_sizeuintcount of methods annotated by this itemannotated_parameters_sizeuintcount of method parameter lists annotated by this itemfield_annotationsfield_annotation[fields_size] (optional)list of associated field annotations. The elements of the list must be sorted in increasing order, byfield_idx.method_annotationsmethod_annotation[methods_size] (optional)list of associated method annotations. The elements of the list must be sorted in increasing order, bymethod_idx.parameter_annotationsparameter_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

NameFormatDescriptionfield_idxuintindex into the field_ids list for the identity of the field being annotatedannotations_offuintoffset from the start of the file to the list of annotations for the field. The offset should be to a location in thedata section. The format of the data is specified by "annotation_set_item" below.

method_annotation Format

NameFormatDescriptionmethod_idxuintindex into the method_ids list for the identity of the method being annotatedannotations_offuintoffset from the start of the file to the list of annotations for the method. The offset should be to a location in thedata section. The format of the data is specified by "annotation_set_item" below.

parameter_annotation Format

NameFormatDescriptionmethod_idxuintindex into the method_ids list for the identity of the method whose parameters are being annotatedannotations_offuintoffset from the start of the file to the list of annotations for the method parameters. The offset should be to a location in thedata 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

NameFormatDescriptionsizeuintsize of the list, in entrieslistannotation_set_ref_item[size]elements of the list

annotation_set_ref_item Format

NameFormatDescriptionannotations_offuintoffset 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 thedata 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, andannotation_set_ref_item

appears in the data section

alignment: 4 bytes

NameFormatDescriptionsizeuintsize of the set, in entriesentriesannotation_off_item[size]elements of the set. The elements must be sorted in increasing order, by type_idx.

annotation_off_item Format

NameFormatDescriptionannotation_offuintoffset from the start of the file to an annotation. The offset should be to a location in thedata 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)

NameFormatDescriptionvisibilityubyteintended visibility of this annotation (see below)annotationencoded_annotationencoded 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:

NameValueDescriptionVISIBILITY_BUILD0x00intended only to be visible at build time (e.g., during compilation of other code)VISIBILITY_RUNTIME0x01intended to visible at runtimeVISIBILITY_SYSTEM0x02intended 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)

NameFormatDescriptionvalueencoded_arraybytes 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 toVISIBILITY_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.

NameFormatDescriptionvalueAnnotationthe 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 anEnclosingClass and anEnclosingMethod annotation.

NameFormatDescriptionvalueClassthe 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 anInnerClass annotation. Additionally, a class may not have both anEnclosingClass and an EnclosingMethod annotation.

NameFormatDescriptionvalueMethodthe 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 haveeither anEnclosingClass annotationor anEnclosingMethod annotation.

NameFormatDescriptionnameStringthe originally declared simple name of this class (not including any package prefix). If this class is anonymous, then the name isnull.accessFlagsintthe 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.)

NameFormatDescriptionvalueClass[]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 atype_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 anarray 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.

NameFormatDescriptionvalueString[]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.

NameFormatDescriptionvalueClass[]the array of exception types thrown