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<h1>Dalvik VM Instruction Formats</h1>
<p>Copyright © 2007 The Android Open Source Project
<h2>Introduction and Overview</h2>
<p>This document lists the instruction formats used by Dalvik bytecode
and is meant to be used in conjunction with the
<a href="dalvik-bytecode.html">bytecode reference document</a>.</p>
<h3>Bitwise descriptions</h3>
<p>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
("<code>|</code>") interspersed to aid in reading. Uppercase letters
in sequence from "<code>A</code>" are used to indicate fields within
the format (which then get defined further by the syntax column). The term
"<code>op</code>" is used to indicate the position of the eight-bit
opcode within the format. A slashed zero ("<code>Ø</code>") is
used to indicate that all bits should be zero in the indicated
position.</p>
<p>For example, the format "<code>B|A|<i>op</i> CCCC</code>" 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.</p>
<h3>Format IDs</h3>
<p>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.</p>
<p>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 accomodate a variable
number of registers), with the special designation "<code>r</code>" 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 "<code>21t</code>" is of length two, contains one register reference,
and additionally contains a branch target.</p>
<p>Suggested static linking formats have an additional "<code>s</code>" suffix,
making them four characters total.</p>
<p>The full list of typecode letters are as follows. Note that some
forms have different sizes, depending on the format:</p>
<table class="letters">
<thead>
<tr>
<th>Mnemonic</th>
<th>Bit Sizes</th>
<th>Meaning</th>
</tr>
</thead>
<tbody>
<tr>
<td>b</td>
<td>8</td>
<td>immediate signed <b>b</b>yte</td>
</tr>
<tr>
<td>c</td>
<td>16, 32</td>
<td><b>c</b>onstant pool index</td>
</tr>
<tr>
<td>f</td>
<td>16</td>
<td>inter<b>f</b>ace constants (only used in statically linked formats)
</td>
</tr>
<tr>
<td>h</td>
<td>16</td>
<td>immediate signed <b>h</b>at (high-order bits of a 32- or 64-bit
value; low-order bits are all <code>0</code>)
</td>
</tr>
<tr>
<td>i</td>
<td>32</td>
<td>immediate signed <b>i</b>nt, or 32-bit float</td>
</tr>
<tr>
<td>l</td>
<td>64</td>
<td>immediate signed <b>l</b>ong, or 64-bit double</td>
</tr>
<tr>
<td>m</td>
<td>16</td>
<td><b>m</b>ethod constants (only used in statically linked formats)</td>
</tr>
<tr>
<td>n</td>
<td>4</td>
<td>immediate signed <b>n</b>ibble</td>
</tr>
<tr>
<td>s</td>
<td>16</td>
<td>immediate signed <b>s</b>hort</td>
</tr>
<tr>
<td>t</td>
<td>8, 16, 32</td>
<td>branch <b>t</b>arget</td>
</tr>
<tr>
<td>x</td>
<td>0</td>
<td>no additional data</td>
</tr>
</tbody>
</table>
<h3>Syntax</h3>
<p>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.</p>
<p>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
"<code>BB</code>" in the first column would also be labeled
"<code>BB</code>" in the syntax column.</p>
<p>Arguments which name a register have the form "<code>v<i>X</i></code>".
The prefix "<code>v</code>" was chosen instead of the more common
"<code>r</code>" exactly to avoid conflicting with (non-virtual) architectures
on which a Dalvik virtual machine might be implemented which themselves
use the prefix "<code>r</code>" for their registers. (That is, this
decision makes it possible to talk about both virtual and real registers
together without the need for circumlocution.)</p>
<p>Arguments which indicate a literal value have the form
"<code>#+<i>X</i></code>". 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.</p>
<p>Arguments which indicate a relative instruction address offset have the
form "<code>+<i>X</i></code>".</p>
<p>Arguments which indicate a literal constant pool index have the form
"<code><i>kind</i>@<i>X</i></code>", where "<code><i>kind</i></code>"
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 four
kinds of constant pool are "<code>string</code>" (string pool index),
"<code>type</code>" (type pool index), "<code>field</code>" (field
pool index), and "<code>meth</code>" (method pool index).</p>
<p>Similar to the representation of constant pool indices, there are
also suggested (optional) forms that indicate prelinked offsets or
indices. These prelinked values include "<code>vtaboff</code>"
(vtable offset), "<code>fieldoff</code>" (field offset), and
"<code>iface</code>" (interface pool index).</p>
<p>In the cases where a format value isn't explictly part of the syntax
but instead picks a variant, each variant is listed with the prefix
"<code>[<i>X</i>=<i>N</i>]</code>" (e.g., "<code>[B=2]</code>") to indicate
the correspondence.</p>
<h2>The Formats</h2>
<table class="format">
<thead>
<tr>
<th>Format</th>
<th>ID</th>
<th>Syntax</th>
<th>Notable Opcodes Covered</th>
</tr>
</thead>
<tbody>
<tr>
<td>ØØ|<i>op</i></td>
<td>10x</td>
<td><i><code>op</code></i></td>
<td> </td>
</tr>
<tr>
<td rowspan="2">B|A|<i>op</i></td>
<td>12x</td>
<td><i><code>op</code></i> vA, vB</td>
<td> </td>
</tr>
<tr>
<td>11n</td>
<td><i><code>op</code></i> vA, #+B</td>
<td> </td>
</tr>
<tr>
<td rowspan="2">AA|<i>op</i></td>
<td>11x</td>
<td><i><code>op</code></i> vAA</td>
<td> </td>
</tr>
<tr>
<td>10t</td>
<td><i><code>op</code></i> +AA</td>
<td>goto</td>
</tr>
<tr>
<td>ØØ|<i>op</i> AAAA</td></td>
<td>20t</td>
<td><i><code>op</code></i> +AAAA</td>
<td>goto/16</td>
</tr>
<tr>
<td rowspan="5">AA|<i>op</i> BBBB</td>
<td>22x</td>
<td><i><code>op</code></i> vAA, vBBBB</td>
<td> </td>
</tr>
<tr>
<td>21t</td>
<td><i><code>op</code></i> vAA, +BBBB</td>
<td> </td>
</tr>
<tr>
<td>21s</td>
<td><i><code>op</code></i> vAA, #+BBBB</td>
<td> </td>
</tr>
<tr>
<td>21h</td>
<td><i><code>op</code></i> vAA, #+BBBB0000<br/>
<i><code>op</code></i> vAA, #+BBBB000000000000
</td>
<td> </td>
</tr>
<tr>
<td>21c</td>
<td><i><code>op</code></i> vAA, type@BBBB<br/>
<i><code>op</code></i> vAA, field@BBBB<br/>
<i><code>op</code></i> vAA, string@BBBB
</td>
<td>check-cast<br/>
const-class<br/>
const-string
</td>
</tr>
<tr>
<td rowspan="2">AA|<i>op</i> CC|BB</td>
<td>23x</td>
<td><i><code>op</code></i> vAA, vBB, vCC</td>
<td> </td>
</tr>
<tr>
<td>22b</td>
<td><i><code>op</code></i> vAA, vBB, #+CC</td>
<td> </td>
</tr>
<tr>
<td rowspan="4">B|A|<i>op</i> CCCC</td>
<td>22t</td>
<td><i><code>op</code></i> vA, vB, +CCCC</td>
<td> </td>
</tr>
<tr>
<td>22s</td>
<td><i><code>op</code></i> vA, vB, #+CCCC</td>
<td> </td>
</tr>
<tr>
<td>22c</td>
<td><i><code>op</code></i> vA, vB, type@CCCC<br/>
<i><code>op</code></i> vA, vB, field@CCCC
</td>
<td>instance-of</td>
</tr>
<tr>
<td>22cs</td>
<td><i><code>op</code></i> vA, vB, fieldoff@CCCC</td>
<td><i>(suggested format for statically linked field access instructions of
format 22c)</i>
</td>
</tr>
<tr>
<td>ØØ|<i>op</i> AAAA<sub>lo</sub> AAAA<sub>hi</sub></td></td>
<td>30t</td>
<td><i><code>op</code></i> +AAAAAAAA</td>
<td>goto/32</td>
</tr>
<tr>
<td>ØØ|<i>op</i> AAAA BBBB</td>
<td>32x</td>
<td><i><code>op</code></i> vAAAA, vBBBB</td>
<td> </td>
</tr>
<tr>
<td rowspan="3">AA|<i>op</i> BBBB<sub>lo</sub> BBBB<sub>hi</sub></td>
<td>31i</td>
<td><i><code>op</code></i> vAA, #+BBBBBBBB</td>
<td> </td>
</tr>
<tr>
<td>31t</td>
<td><i><code>op</code></i> vAA, +BBBBBBBB</td>
<td> </td>
</tr>
<tr>
<td>31c</td>
<td><i><code>op</code></i> vAA, string@BBBBBBBB</td>
<td>const-string/jumbo</td>
</tr>
<tr>
<td>B|A|<i>op</i> CCCC G|F|E|D</td>
<td>35c</td>
<td><i>[<code>B=5</code>] <code>op</code></i> {vD, vE, vF, vG, vA},
meth@CCCC<br/>
<i>[<code>B=5</code>] <code>op</code></i> {vD, vE, vF, vG, vA},
type@CCCC<br/>
<i>[<code>B=4</code>] <code>op</code></i> {vD, vE, vF, vG},
<i><code>kind</code></i>@CCCC<br/>
<i>[<code>B=3</code>] <code>op</code></i> {vD, vE, vF},
<i><code>kind</code></i>@CCCC<br/>
<i>[<code>B=2</code>] <code>op</code></i> {vD, vE},
<i><code>kind</code></i>@CCCC<br/>
<i>[<code>B=1</code>] <code>op</code></i> {vD},
<i><code>kind</code></i>@CCCC<br/>
<i>[<code>B=0</code>] <code>op</code></i> {},
<i><code>kind</code></i>@CCCC
</td>
<td> </td>
</tr>
<tr>
<td>B|A|<i>op</i> CCCC G|F|E|D</td>
<td>35ms</td>
<td><i>[<code>B=5</code>] <code>op</code></i> {vD, vE, vF, vG, vA},
vtaboff@CCCC<br/>
<i>[<code>B=4</code>] <code>op</code></i> {vD, vE, vF, vG},
vtaboff@CCCC<br/>
<i>[<code>B=3</code>] <code>op</code></i> {vD, vE, vF},
vtaboff@CCCC<br/>
<i>[<code>B=2</code>] <code>op</code></i> {vD, vE},
vtaboff@CCCC<br/>
<i>[<code>B=1</code>] <code>op</code></i> {vD},
vtaboff@CCCC<br/>
</td>
<td><i>(suggested format for statically linked <code>invoke-virtual</code>
and <code>invoke-super</code> instructions of format 35c)</i>
</td>
</tr>
<tr>
<td>B|A|<i>op</i> DDCC H|G|F|E</td>
<td>35fs</td>
<td><i>[<code>B=5</code>] <code>op</code></i> {vE, vF, vG, vH, vA},
vtaboff@CC, iface@DD<br/>
<i>[<code>B=4</code>] <code>op</code></i> {vE, vF, vG, vH},
vtaboff@CC, iface@DD<br/>
<i>[<code>B=3</code>] <code>op</code></i> {vE, vF, vG},
vtaboff@CC, iface@DD<br/>
<i>[<code>B=2</code>] <code>op</code></i> {vE, vF},
vtaboff@CC, iface@DD<br/>
<i>[<code>B=1</code>] <code>op</code></i> {vE},
vtaboff@CC, iface@DD<br/>
</td>
<td><i>(suggested format for statically linked <code>invoke-interface</code>
instructions of format 35c)</i>
</td>
</tr>
<tr>
<td>AA|<i>op</i> BBBB CCCC</td>
<td>3rc</td>
<td><i><code>op</code></i> {vCCCC .. vNNNN}, meth@BBBB<br/>
<i><code>op</code></i> {vCCCC .. vNNNN}, type@BBBB<br/>
<p><i>(where <code>NNNN = CCCC+AA-1</code>, that is <code>A</code>
determines the count <code>0..255</code>, and <code>C</code>
determines the first register)</i></p>
</td>
<td> </td>
</tr>
<tr>
<td>AA|<i>op</i> BBBB CCCC</td>
<td>3rms</td>
<td><i><code>op</code></i> {vCCCC .. vNNNN}, vtaboff@BBBB<br/>
<p><i>(where <code>NNNN = CCCC+AA-1</code>, that is <code>A</code>
determines the count <code>0..255</code>, and <code>C</code>
determines the first register)</i></p>
</td>
<td><i>(suggested format for statically linked <code>invoke-virtual</code>
and <code>invoke-super</code> instructions of format <code>3rc</code>)</i>
</td>
</tr>
<tr>
<td>AA|<i>op</i> CCBB DDDD</td>
<td>3rfs</td>
<td><i><code>op</code></i> {vDDDD .. vNNNN}, vtaboff@BB,
iface@CC<br/>
<p><i>(where <code>NNNN = DDDD+AA-1</code>, that is <code>A</code>
determines the count <code>0..255</code>, and <code>D</code>
determines the first register)</i></p>
</td>
<td><i>(suggested format for statically linked <code>invoke-interface</code>
instructions of format <code>3rc</code>)</i>
</td>
</tr>
<tr>
<td>AA|<i>op</i> BBBB<sub>lo</sub> BBBB BBBB BBBB<sub>hi</sub></td>
<td>51l</td>
<td><i><code>op</code></i> vAA, #+BBBBBBBBBBBBBBBB</td>
<td>const-wide</td>
</tr>
</tbody>
</table>
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