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<h5 class="subsubsection">9.41.3.4 Instruction Formats</h5>

<p><a name="index-instruction-formats_002c-s390-2074"></a><a name="index-s390-instruction-formats-2075"></a>
The Principles of Operation manuals lists 26 instruction formats where
some of the formats have multiple variants. For the &lsquo;<samp><span class="samp">.insn</span></samp>&rsquo;
pseudo directive the assembler recognizes some of the formats. 
Typically, the most general variant of the instruction format is used
by the &lsquo;<samp><span class="samp">.insn</span></samp>&rsquo; directive.

   <p>The following table lists the abbreviations used in the table of
instruction formats:

<pre class="display">
     <p><table summary=""><tr align="left"><td valign="top">OpCode / OpCd </td><td valign="top">Part of the op code.
     <br></td></tr><tr align="left"><td valign="top">Bx </td><td valign="top">Base register number for operand x.
     <br></td></tr><tr align="left"><td valign="top">Dx </td><td valign="top">Displacement for operand x.
     <br></td></tr><tr align="left"><td valign="top">DLx </td><td valign="top">Displacement lower 12 bits for operand x.
     <br></td></tr><tr align="left"><td valign="top">DHx </td><td valign="top">Displacement higher 8-bits for operand x.
     <br></td></tr><tr align="left"><td valign="top">Rx </td><td valign="top">Register number for operand x.
     <br></td></tr><tr align="left"><td valign="top">Xx </td><td valign="top">Index register number for operand x.
     <br></td></tr><tr align="left"><td valign="top">Ix </td><td valign="top">Signed immediate for operand x.
     <br></td></tr><tr align="left"><td valign="top">Ux </td><td valign="top">Unsigned immediate for operand x.
     <br></td></tr></table>
</pre>
   <p>An instruction is two, four, or six bytes in length and must be aligned
on a 2 byte boundary. The first two bits of the instruction specify the
length of the instruction, 00 indicates a two byte instruction, 01 and 10
indicates a four byte instruction, and 11 indicates a six byte instruction.

   <p>The following table lists the s390 instruction formats that are available
with the &lsquo;<samp><span class="samp">.insn</span></samp>&rsquo; pseudo directive:

     <dl>
<dt><code>E format</code><dd><pre class="verbatim">     +-------------+
     |    OpCode   |
     +-------------+
     0            15
</pre>

     <br><dt><code>RI format: &lt;insn&gt; R1,I2</code><dd><pre class="verbatim">     +--------+----+----+------------------+
     | OpCode | R1 |OpCd|        I2        |
     +--------+----+----+------------------+
     0        8    12   16                31
</pre>

     <br><dt><code>RIE format: &lt;insn&gt; R1,R3,I2</code><dd><pre class="verbatim">     +--------+----+----+------------------+--------+--------+
     | OpCode | R1 | R3 |        I2        |////////| OpCode |
     +--------+----+----+------------------+--------+--------+
     0        8    12   16                 32       40      47
</pre>

     <br><dt><code>RIL format: &lt;insn&gt; R1,I2</code><dd><pre class="verbatim">     +--------+----+----+------------------------------------+
     | OpCode | R1 |OpCd|                  I2                |
     +--------+----+----+------------------------------------+
     0        8    12   16                                  47
</pre>

     <br><dt><code>RILU format: &lt;insn&gt; R1,U2</code><dd><pre class="verbatim">     +--------+----+----+------------------------------------+
     | OpCode | R1 |OpCd|                  U2                |
     +--------+----+----+------------------------------------+
     0        8    12   16                                  47
</pre>

     <br><dt><code>RIS format: &lt;insn&gt; R1,I2,M3,D4(B4)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+--------+--------+
     | OpCode | R1 | M3 | B4 |     D4      |   I2   | Opcode |
     +--------+----+----+----+-------------+--------+--------+
     0        8    12   16   20            32       36      47
</pre>

     <br><dt><code>RR format: &lt;insn&gt; R1,R2</code><dd><pre class="verbatim">     +--------+----+----+
     | OpCode | R1 | R2 |
     +--------+----+----+
     0        8    12  15
</pre>

     <br><dt><code>RRE format: &lt;insn&gt; R1,R2</code><dd><pre class="verbatim">     +------------------+--------+----+----+
     |      OpCode      |////////| R1 | R2 |
     +------------------+--------+----+----+
     0                  16       24   28  31
</pre>

     <br><dt><code>RRF format: &lt;insn&gt; R1,R2,R3,M4</code><dd><pre class="verbatim">     +------------------+----+----+----+----+
     |      OpCode      | R3 | M4 | R1 | R2 |
     +------------------+----+----+----+----+
     0                  16   20   24   28  31
</pre>

     <br><dt><code>RRS format: &lt;insn&gt; R1,R2,M3,D4(B4)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+----+----+--------+
     | OpCode | R1 | R3 | B4 |     D4      | M3 |////| OpCode |
     +--------+----+----+----+-------------+----+----+--------+
     0        8    12   16   20            32   36   40      47
</pre>

     <br><dt><code>RS format: &lt;insn&gt; R1,R3,D2(B2)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+
     | OpCode | R1 | R3 | B2 |     D2      |
     +--------+----+----+----+-------------+
     0        8    12   16   20           31
</pre>

     <br><dt><code>RSE format: &lt;insn&gt; R1,R3,D2(B2)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+--------+--------+
     | OpCode | R1 | R3 | B2 |     D2      |////////| OpCode |
     +--------+----+----+----+-------------+--------+--------+
     0        8    12   16   20            32       40      47
</pre>

     <br><dt><code>RSI format: &lt;insn&gt; R1,R3,I2</code><dd><pre class="verbatim">     +--------+----+----+------------------------------------+
     | OpCode | R1 | R3 |                  I2                |
     +--------+----+----+------------------------------------+
     0        8    12   16                                  47
</pre>

     <br><dt><code>RSY format: &lt;insn&gt; R1,R3,D2(B2)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+--------+--------+
     | OpCode | R1 | R3 | B2 |    DL2      |  DH2   | OpCode |
     +--------+----+----+----+-------------+--------+--------+
     0        8    12   16   20            32       40      47
</pre>

     <br><dt><code>RX format: &lt;insn&gt; R1,D2(X2,B2)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+
     | OpCode | R1 | X2 | B2 |     D2      |
     +--------+----+----+----+-------------+
     0        8    12   16   20           31
</pre>

     <br><dt><code>RXE format: &lt;insn&gt; R1,D2(X2,B2)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+--------+--------+
     | OpCode | R1 | X2 | B2 |     D2      |////////| OpCode |
     +--------+----+----+----+-------------+--------+--------+
     0        8    12   16   20            32       40      47
</pre>

     <br><dt><code>RXF format: &lt;insn&gt; R1,R3,D2(X2,B2)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+----+---+--------+
     | OpCode | R3 | X2 | B2 |     D2      | R1 |///| OpCode |
     +--------+----+----+----+-------------+----+---+--------+
     0        8    12   16   20            32   36  40      47
</pre>

     <br><dt><code>RXY format: &lt;insn&gt; R1,D2(X2,B2)</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+--------+--------+
     | OpCode | R1 | X2 | B2 |     DL2     |   DH2  | OpCode |
     +--------+----+----+----+-------------+--------+--------+
     0        8    12   16   20            32   36   40      47
</pre>

     <br><dt><code>S format: &lt;insn&gt; D2(B2)</code><dd><pre class="verbatim">     +------------------+----+-------------+
     |      OpCode      | B2 |     D2      |
     +------------------+----+-------------+
     0                  16   20           31
</pre>

     <br><dt><code>SI format: &lt;insn&gt; D1(B1),I2</code><dd><pre class="verbatim">     +--------+---------+----+-------------+
     | OpCode |   I2    | B1 |     D1      |
     +--------+---------+----+-------------+
     0        8         16   20           31
</pre>

     <br><dt><code>SIY format: &lt;insn&gt; D1(B1),U2</code><dd><pre class="verbatim">     +--------+---------+----+-------------+--------+--------+
     | OpCode |   I2    | B1 |     DL1     |  DH1   | OpCode |
     +--------+---------+----+-------------+--------+--------+
     0        8         16   20            32   36   40      47
</pre>

     <br><dt><code>SIL format: &lt;insn&gt; D1(B1),I2</code><dd><pre class="verbatim">     +------------------+----+-------------+-----------------+
     |      OpCode      | B1 |      D1     |       I2        |
     +------------------+----+-------------+-----------------+
     0                  16   20            32               47
</pre>

     <br><dt><code>SS format: &lt;insn&gt; D1(R1,B1),D2(B3),R3</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+----+------------+
     | OpCode | R1 | R3 | B1 |     D1      | B2 |     D2     |
     +--------+----+----+----+-------------+----+------------+
     0        8    12   16   20            32   36          47
</pre>

     <br><dt><code>SSE format: &lt;insn&gt; D1(B1),D2(B2)</code><dd><pre class="verbatim">     +------------------+----+-------------+----+------------+
     |      OpCode      | B1 |     D1      | B2 |     D2     |
     +------------------+----+-------------+----+------------+
     0        8    12   16   20            32   36           47
</pre>

     <br><dt><code>SSF format: &lt;insn&gt; D1(B1),D2(B2),R3</code><dd><pre class="verbatim">     +--------+----+----+----+-------------+----+------------+
     | OpCode | R3 |OpCd| B1 |     D1      | B2 |     D2     |
     +--------+----+----+----+-------------+----+------------+
     0        8    12   16   20            32   36           47
</pre>

   </dl>

   <p>For the complete list of all instruction format variants see the
Principles of Operation manuals.

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