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| Next: <a href="RX_002dDirectives.html#RX_002dDirectives" accesskey="n" rel="next">RX-Directives</a>, Previous: <a href="RX_002dOpts.html#RX_002dOpts" accesskey="p" rel="prev">RX-Opts</a>, Up: <a href="RX_002dDependent.html#RX_002dDependent" accesskey="u" rel="up">RX-Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Symbolic-Operand-Modifiers-3"></a> |
| <h4 class="subsection">9.36.2 Symbolic Operand Modifiers</h4> |
| |
| <a name="index-RX-modifiers"></a> |
| <a name="index-syntax_002c-RX"></a> |
| <a name="index-_0025gp"></a> |
| |
| <p>The assembler supports one modifier when using symbol addresses |
| in RX instruction operands. The general syntax is the following: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">%gp(symbol) |
| </pre></div> |
| |
| <p>The modifier returns the offset from the <var>__gp</var> symbol to the |
| specified symbol as a 16-bit value. The intent is that this offset |
| should be used in a register+offset move instruction when generating |
| references to small data. Ie, like this: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample"> mov.W %gp(_foo)[%gpreg], r1 |
| </pre></div> |
| |
| <p>The assembler also supports two meta register names which can be used |
| to refer to registers whose values may not be known to the |
| programmer. These meta register names are: |
| </p> |
| <dl compact="compact"> |
| <dd> |
| <a name="index-_0025gpreg"></a> |
| </dd> |
| <dt><code>%gpreg</code></dt> |
| <dd><p>The small data address register. |
| </p> |
| <a name="index-_0025pidreg"></a> |
| </dd> |
| <dt><code>%pidreg</code></dt> |
| <dd><p>The PID base address register. |
| </p> |
| </dd> |
| </dl> |
| |
| <p>Both registers normally have the value r13, but this can change if |
| some registers have been reserved for use by interrupt handlers or if |
| both the small data limit and position independent data features are |
| being used at the same time. |
| </p> |
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