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| <h4 class="subsection">9.40.2 Symbolic Operand Modifiers</h4> |
| |
| <p><a name="index-RX-modifiers-2030"></a><a name="index-syntax_002c-RX-2031"></a><a name="index-g_t_0025gp-2032"></a> |
| The assembler supports one modifier when using symbol addresses |
| in RX instruction operands. The general syntax is the following: |
| |
| <pre class="smallexample"> %gp(symbol) |
| </pre> |
| <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: |
| |
| <pre class="smallexample"> mov.W %gp(_foo)[%gpreg], r1 |
| </pre> |
| <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: |
| |
| |
| <a name="index-g_t_0040samp_007b_0025gpreg_007d-2033"></a> |
| <dl><dt><code>%gpreg</code><dd>The small data address register. |
| |
| <p><a name="index-g_t_0040samp_007b_0025pidreg_007d-2034"></a><br><dt><code>%pidreg</code><dd>The PID base address register. |
| |
| </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. |
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