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<a name="ESA_002f390-Directives"></a>Next:&nbsp;<a rel="next" accesskey="n" href="ESA_002f390-Opcodes.html#ESA_002f390-Opcodes">ESA/390 Opcodes</a>,
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<h4 class="subsection">9.12.5 ESA/390 Assembler Directives</h4>
<p><code>as</code> for the ESA/390 supports all of the standard ELF/SVR4
assembler directives that are documented in the main part of this
documentation. Several additional directives are supported in order
to implement the ESA/390 addressing model. The most important of these
are <code>.using</code> and <code>.ltorg</code>
<p><a name="index-ESA_002f390_002donly-directives-813"></a>These are the additional directives in <code>as</code> for the ESA/390:
<dl>
<dt><code>.dc</code><dd>A small subset of the usual DC directive is supported.
<br><dt><code>.drop </code><var>regno</var><dd>Stop using <var>regno</var> as the base register. The <var>regno</var> must
have been previously declared with a <code>.using</code> directive in the
same section as the current section.
<br><dt><code>.ebcdic </code><var>string</var><dd>Emit the EBCDIC equivalent of the indicated string. The emitted string
will be null terminated. Note that the directives <code>.string</code> etc. emit
ascii strings by default.
<br><dt><code>EQU</code><dd>The standard HLASM-style EQU directive is not supported; however, the
standard <code>as</code> directive .equ can be used to the same effect.
<br><dt><code>.ltorg</code><dd>Dump the literal pool accumulated so far; begin a new literal pool.
The literal pool will be written in the current section; in order to
generate correct assembly, a <code>.using</code> must have been previously
specified in the same section.
<br><dt><code>.using </code><var>expr</var><code>,</code><var>regno</var><dd>Use <var>regno</var> as the base register for all subsequent RX, RS, and SS form
instructions. The <var>expr</var> will be evaluated to obtain the base address;
usually, <var>expr</var> will merely be <span class="samp">*</span>.
<p>This assembler allows two <code>.using</code> directives to be simultaneously
outstanding, one in the <code>.text</code> section, and one in another section
(typically, the <code>.data</code> section). This feature allows
dynamically loaded objects to be implemented in a relatively
straightforward way. A <code>.using</code> directive must always be specified
in the <code>.text</code> section; this will specify the base register that
will be used for branches in the <code>.text</code> section. A second
<code>.using</code> may be specified in another section; this will specify
the base register that is used for non-label address literals.
When a second <code>.using</code> is specified, then the subsequent
<code>.ltorg</code> must be put in the same section; otherwise an error will
result.
<p>Thus, for example, the following code uses <code>r3</code> to address branch
targets and <code>r4</code> to address the literal pool, which has been written
to the <code>.data</code> section. The is, the constants <code>=A(some_routine)</code>,
<code>=H'42'</code> and <code>=E'3.1416'</code> will all appear in the <code>.data</code>
section.
<pre class="example"> .data
.using LITPOOL,r4
.text
BASR r3,0
.using *,r3
B START
.long LITPOOL
START:
L r4,4(,r3)
L r15,=A(some_routine)
LTR r15,r15
BNE LABEL
AH r0,=H'42'
LABEL:
ME r6,=E'3.1416'
.data
LITPOOL:
.ltorg
</pre>
<p>Note that this dual-<code>.using</code> directive semantics extends
and is not compatible with HLASM semantics. Note that this assembler
directive does not support the full range of HLASM semantics.
</dl>
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