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<title>Using as: ARM Opcodes</title>

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<a name="ARM-Opcodes"></a>
<div class="header">
<p>
Next: <a href="ARM-Mapping-Symbols.html#ARM-Mapping-Symbols" accesskey="n" rel="next">ARM Mapping Symbols</a>, Previous: <a href="ARM-Directives.html#ARM-Directives" accesskey="p" rel="previous">ARM Directives</a>, Up: <a href="ARM_002dDependent.html#ARM_002dDependent" accesskey="u" rel="up">ARM-Dependent</a> &nbsp; [<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>
</div>
<hr>
<a name="Opcodes-3"></a>
<h4 class="subsection">9.4.5 Opcodes</h4>

<a name="index-ARM-opcodes"></a>
<a name="index-opcodes-for-ARM"></a>
<p><code>as</code> implements all the standard ARM opcodes.  It also
implements several pseudo opcodes, including several synthetic load
instructions.
</p>
<dl compact="compact">
<dd>
<a name="index-NOP-pseudo-op_002c-ARM"></a>
</dd>
<dt><code>NOP</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">  nop
</pre></div>

<p>This pseudo op will always evaluate to a legal ARM instruction that does
nothing.  Currently it will evaluate to MOV r0, r0.
</p>
<a name="index-LDR-reg_002c_003d_003clabel_003e-pseudo-op_002c-ARM"></a>
</dd>
<dt><code>LDR</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">  ldr &lt;register&gt; , = &lt;expression&gt;
</pre></div>

<p>If expression evaluates to a numeric constant then a MOV or MVN
instruction will be used in place of the LDR instruction, if the
constant can be generated by either of these instructions.  Otherwise
the constant will be placed into the nearest literal pool (if it not
already there) and a PC relative LDR instruction will be generated.
</p>
<a name="index-ADR-reg_002c_003clabel_003e-pseudo-op_002c-ARM"></a>
</dd>
<dt><code>ADR</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">  adr &lt;register&gt; &lt;label&gt;
</pre></div>

<p>This instruction will load the address of <var>label</var> into the indicated
register.  The instruction will evaluate to a PC relative ADD or SUB
instruction depending upon where the label is located.  If the label is
out of range, or if it is not defined in the same file (and section) as
the ADR instruction, then an error will be generated.  This instruction
will not make use of the literal pool.
</p>
<p>If <var>label</var> is a thumb function symbol, and thumb interworking has
been enabled via the <samp>-mthumb-interwork</samp> option then the bottom
bit of the value stored into <var>register</var> will be set.  This allows
the following sequence to work as expected:
</p>
<div class="smallexample">
<pre class="smallexample">  adr     r0, thumb_function
  blx     r0
</pre></div>

<a name="index-ADRL-reg_002c_003clabel_003e-pseudo-op_002c-ARM"></a>
</dd>
<dt><code>ADRL</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">  adrl &lt;register&gt; &lt;label&gt;
</pre></div>

<p>This instruction will load the address of <var>label</var> into the indicated
register.  The instruction will evaluate to one or two PC relative ADD
or SUB instructions depending upon where the label is located.  If a
second instruction is not needed a NOP instruction will be generated in
its place, so that this instruction is always 8 bytes long.
</p>
<p>If the label is out of range, or if it is not defined in the same file
(and section) as the ADRL instruction, then an error will be generated.
This instruction will not make use of the literal pool.
</p>
<p>If <var>label</var> is a thumb function symbol, and thumb interworking has
been enabled via the <samp>-mthumb-interwork</samp> option then the bottom
bit of the value stored into <var>register</var> will be set.
</p>
</dd>
</dl>

<p>For information on the ARM or Thumb instruction sets, see <cite>ARM
Software Development Toolkit Reference Manual</cite>, Advanced RISC Machines
Ltd.
</p>
<hr>
<div class="header">
<p>
Next: <a href="ARM-Mapping-Symbols.html#ARM-Mapping-Symbols" accesskey="n" rel="next">ARM Mapping Symbols</a>, Previous: <a href="ARM-Directives.html#ARM-Directives" accesskey="p" rel="previous">ARM Directives</a>, Up: <a href="ARM_002dDependent.html#ARM_002dDependent" accesskey="u" rel="up">ARM-Dependent</a> &nbsp; [<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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