This page lists the instruction formats used by the Dalvik executable (DEX) format and Dalvik bytecode. It is meant to be used in conjunction with the bytecode reference document.
Bitwise descriptions
The first column in the format table lists the bitwise layout of
the format. It consists of one or more space-separated "words" each of
which describes a 16-bit code unit. Each character in a word
represents four bits, read from high bits to low, with vertical bars
("|") interspersed to aid in reading. Uppercase letters
in sequence from "A" are used to indicate fields within
the format (which then get defined further by the syntax column). The term
"op" is used to indicate the position of an eight-bit
opcode within the format. A slashed zero
("Ø") is used to indicate that all bits must be
zero in the indicated position.
For the most part, lettering proceeds from earlier code units to later code units, and low-order to high-order within a code unit. However, there are a few exceptions to this general rule, which are done in order to make the naming of similar-meaning parts be the same across different instruction formats. These cases are noted explicitly in the format descriptions.
For example, the format "B|A|op CCCC" indicates
that the format consists of two 16-bit code units. The first word
consists of the opcode in the low eight bits and a pair of four-bit
values in the high eight bits; and the second word consists of a single
16-bit value.
Format IDs
The second column in the format table indicates the short identifier for the format, which is used in other documents and in code to identify the format.
Most format IDs consist of three characters, two digits followed by a
letter. The first digit indicates the number of 16-bit code units in the
format. The second digit indicates the maximum number of registers that the
format contains (maximum, since some formats can accommodate a variable
number of registers), with the special designation "r" indicating
that a range of registers is encoded. The final letter semi-mnemonically
indicates the type of any extra data encoded by the format. For example,
format "21t" is of length two, contains one register reference,
and additionally contains a branch target.
Suggested static linking formats have an additional
"s" suffix, making them four characters total. Similarly,
suggested "inline" linking formats have an additional "i"
suffix. (In this context, inline linking is like static linking,
except with more direct ties into a machine's implementation.)
Finally, a couple oddball suggested formats (e.g.,
"20bc") include two pieces of data which are both
represented in its format ID.
The full list of typecode letters are as follows. Note that some forms have different sizes, depending on the format:
| Mnemonic | Bit Sizes | Meaning |
|---|---|---|
| b | 8 | immediate signed byte |
| c | 16, 32 | constant pool index |
| f | 16 | interface constants (only used in statically linked formats) |
| h | 16 | immediate signed hat (high-order bits of a 32- or 64-bit
value; low-order bits are all 0)
|
| i | 32 | immediate signed int, or 32-bit float |
| l | 64 | immediate signed long, or 64-bit double |
| m | 16 | method constants (only used in statically linked formats) |
| n | 4 | immediate signed nibble |
| s | 16 | immediate signed short |
| t | 8, 16, 32 | branch target |
| x | 0 | no additional data |
Syntax
The third column of the format table indicates the human-oriented syntax for instructions which use the indicated format. Each instruction starts with the named opcode and is optionally followed by one or more arguments, themselves separated with commas.
Wherever an argument refers to a field from the first column, the
letter for that field is indicated in the syntax, repeated once for
each four bits of the field. For example, an eight-bit field labeled
"BB" in the first column would also be labeled
"BB" in the syntax column.
Arguments which name a register have the form "vX".
The prefix "v" was chosen instead of the more common
"r" exactly to avoid conflicting with (non-virtual) architectures
on which the Dalvik Executable format might be implemented which themselves
use the prefix "r" for their registers. (That is, this
decision makes it possible to talk about both virtual and real registers
together without the need for circumlocution.)
Arguments which indicate a literal value have the form
"#+X". Some formats indicate literals that only
have non-zero bits in their high-order bits; for these, the zeroes
are represented explicitly in the syntax, even though they do not
appear in the bitwise representation.
Arguments which indicate a relative instruction address offset have the
form "+X".
Arguments which indicate a literal constant pool index have the form
"kind@X", where "kind"
indicates which constant pool is being referred to. Each opcode that
uses such a format explicitly allows only one kind of constant; see
the opcode reference to figure out the correspondence. The
kinds of constant pool are "string" (string pool index),
"type" (type pool index), "field" (field
pool index), "meth" (method pool index), and
"site" (call site index).
Similar to the representation of constant pool indices, there are
also suggested (optional) forms that indicate prelinked offsets or
indices. There are two types of suggested prelinked value: vtable offsets
(indicated as "vtaboff") and field offsets (indicated as
"fieldoff").
In the cases where a format value isn't explicitly part of the syntax
but instead picks a variant, each variant is listed with the prefix
"[X=N]" (e.g., "[A=2]") to indicate
the correspondence.
Formats
| Format | ID | Syntax | Notable Opcodes Covered |
|---|---|---|---|
| N/A | 00x | N/A |
pseudo-format used for unused opcodes; suggested for use as the nominal format for a breakpoint opcode |
| ØØ|op | 10x | op |
|
| B|A|op | 12x | op vA, vB |
|
| 11n | op vA, #+B |
||
| AA|op | 11x | op vAA |
|
| 10t | op +AA |
goto | |
| ØØ|op AAAA | 20t | op +AAAA |
goto/16 |
| AA|op BBBB | 20bc | op AA, kind@BBBB |
suggested format for statically determined verification errors; A is the type of error and B is an index into a type-appropriate table (e.g. method references for a no-such-method error) |
| AA|op BBBB | 22x | op vAA, vBBBB |
|
| 21t | op vAA, +BBBB |
||
| 21s | op vAA, #+BBBB |
||
| 21h | op vAA, #+BBBB0000op vAA, #+BBBB000000000000
|
||
| 21c | op vAA, type@BBBBop vAA, field@BBBBop vAA, method_handle@BBBBop vAA, proto@BBBBop vAA, string@BBBB
|
check-cast const-class const-method-handle const-method-type const-string |
|
| AA|op CC|BB | 23x | op vAA, vBB, vCC |
|
| 22b | op vAA, vBB, #+CC |
||
| B|A|op CCCC | 22t | op vA, vB, +CCCC |
|
| 22s | op vA, vB, #+CCCC |
||
| 22c | op vA, vB, type@CCCCop vA, vB, field@CCCC
|
instance-of | |
| 22cs | op vA, vB, fieldoff@CCCC |
suggested format for statically linked field access instructions of format 22c | |
| ØØ|op AAAAlo AAAAhi | 30t | op +AAAAAAAA |
goto/32 |
| ØØ|op AAAA BBBB | 32x | op vAAAA, vBBBB |
|
| AA|op BBBBlo BBBBhi | 31i | op vAA, #+BBBBBBBB |
|
| 31t | op vAA, +BBBBBBBB |
||
| 31c | op vAA, string@BBBBBBBB |
const-string/jumbo | |
| A|G|op BBBB F|E|D|C | 35c | [A=5] op {vC, vD, vE, vF, vG},
meth@BBBB[ A=5] op {vC, vD, vE, vF, vG},
site@BBBB[ A=5] op {vC, vD, vE, vF, vG},
type@BBBB[ A=4] op {vC, vD, vE, vF},
kind@BBBB[ A=3] op {vC, vD, vE},
kind@BBBB[ A=2] op {vC, vD},
kind@BBBB[ A=1] op {vC},
kind@BBBB[ A=0] op {},
kind@BBBBThe unusual choice in lettering here reflects a desire to make the count and the reference index have the same label as in format 3rc. |
|
| 35ms | [A=5] op {vC, vD, vE, vF, vG},
vtaboff@BBBB[ A=4] op {vC, vD, vE, vF},
vtaboff@BBBB[ A=3] op {vC, vD, vE},
vtaboff@BBBB[ A=2] op {vC, vD},
vtaboff@BBBB[ A=1] op {vC},
vtaboff@BBBBThe unusual choice in lettering here reflects a desire to make the count and the reference index have the same label as in format 3rms. |
suggested format for statically linked invoke-virtual
and invoke-super instructions of format 35c
|
|
| 35mi | [A=5] op {vC, vD, vE, vF, vG},
inline@BBBB[ A=4] op {vC, vD, vE, vF},
inline@BBBB[ A=3] op {vC, vD, vE},
inline@BBBB[ A=2] op {vC, vD},
inline@BBBB[ A=1] op {vC},
inline@BBBBThe unusual choice in lettering here reflects a desire to make the count and the reference index have the same label as in format 3rmi. |
suggested format for inline linked invoke-static
and invoke-virtual instructions of format 35c
|
|
| AA|op BBBB CCCC | 3rc | op {vCCCC .. vNNNN}, meth@BBBBop {vCCCC .. vNNNN}, site@BBBBop {vCCCC .. vNNNN}, type@BBBBwhere |
|
| 3rms | op {vCCCC .. vNNNN}, vtaboff@BBBBwhere |
suggested format for statically linked invoke-virtual
and invoke-super instructions of format 3rc
|
|
| 3rmi | op {vCCCC .. vNNNN}, inline@BBBBwhere |
suggested format for inline linked invoke-static
and invoke-virtual instructions of format 3rc
|
|
| A|G|op BBBB F|E|D|C HHHH | 45cc |
[A=5] op {vC, vD, vE, vF, vG}, meth@BBBB, proto@HHHH[ A=4] op {vC, vD, vE, vF}, meth@BBBB, proto@HHHH[ A=3] op {vC, vD, vE}, meth@BBBB, proto@HHHH[ A=2] op {vC, vD}, meth@BBBB, proto@HHHH[ A=1] op {vC}, meth@BBBB, proto@HHHH
|
invoke-polymorphic |
| AA|op BBBB CCCC HHHH | 4rcc |
op> {vCCCC .. vNNNN}, meth@BBBB, proto@HHHH
where |
invoke-polymorphic/range |
| AA|op BBBBlo BBBB BBBB BBBBhi | 51l | op vAA, #+BBBBBBBBBBBBBBBB |
const-wide |