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<a name="Bundle-directives"></a>
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<a name="Bundle-directives-1"></a>
<h3 class="section">7.8 Bundle directives</h3>
<a name="g_t_002ebundle_005falign_005fmode-abs_002dexpr"></a>
<h4 class="subsection">7.8.1 <code>.bundle_align_mode <var>abs-expr</var></code></h4>
<a name="index-bundle_005falign_005fmode-directive"></a>
<a name="index-bundle"></a>
<a name="index-instruction-bundle"></a>
<a name="index-aligned-instruction-bundle"></a>
<p><code>.bundle_align_mode</code> enables or disables <em>aligned instruction
bundle</em> mode.  In this mode, sequences of adjacent instructions are grouped
into fixed-sized <em>bundles</em>.  If the argument is zero, this mode is
disabled (which is the default state).  If the argument it not zero, it
gives the size of an instruction bundle as a power of two (as for the
<code>.p2align</code> directive, see <a href="P2align.html#P2align">P2align</a>).
</p>
<p>For some targets, it&rsquo;s an ABI requirement that no instruction may span a
certain aligned boundary.  A <em>bundle</em> is simply a sequence of
instructions that starts on an aligned boundary.  For example, if
<var>abs-expr</var> is <code>5</code> then the bundle size is 32, so each aligned
chunk of 32 bytes is a bundle.  When aligned instruction bundle mode is in
effect, no single instruction may span a boundary between bundles.  If an
instruction would start too close to the end of a bundle for the length of
that particular instruction to fit within the bundle, then the space at the
end of that bundle is filled with no-op instructions so the instruction
starts in the next bundle.  As a corollary, it&rsquo;s an error if any single
instruction&rsquo;s encoding is longer than the bundle size.
</p>
<a name="g_t_002ebundle_005flock-and-_002ebundle_005funlock"></a>
<h4 class="subsection">7.8.2 <code>.bundle_lock</code> and <code>.bundle_unlock</code></h4>
<a name="index-bundle_005flock-directive"></a>
<a name="index-bundle_005funlock-directive"></a>
<p>The <code>.bundle_lock</code> and directive <code>.bundle_unlock</code> directives
allow explicit control over instruction bundle padding.  These directives
are only valid when <code>.bundle_align_mode</code> has been used to enable
aligned instruction bundle mode.  It&rsquo;s an error if they appear when
<code>.bundle_align_mode</code> has not been used at all, or when the last
directive was <code><span class="nolinebreak">.bundle_align_mode</span>&nbsp;0</code><!-- /@w -->.
</p>
<a name="index-bundle_002dlocked"></a>
<p>For some targets, it&rsquo;s an ABI requirement that certain instructions may
appear only as part of specified permissible sequences of multiple
instructions, all within the same bundle.  A pair of <code>.bundle_lock</code>
and <code>.bundle_unlock</code> directives define a <em>bundle-locked</em>
instruction sequence.  For purposes of aligned instruction bundle mode, a
sequence starting with <code>.bundle_lock</code> and ending with
<code>.bundle_unlock</code> is treated as a single instruction.  That is, the
entire sequence must fit into a single bundle and may not span a bundle
boundary.  If necessary, no-op instructions will be inserted before the
first instruction of the sequence so that the whole sequence starts on an
aligned bundle boundary.  It&rsquo;s an error if the sequence is longer than the
bundle size.
</p>
<p>For convenience when using <code>.bundle_lock</code> and <code>.bundle_unlock</code>
inside assembler macros (see <a href="Macro.html#Macro">Macro</a>), bundle-locked sequences may be
nested.  That is, a second <code>.bundle_lock</code> directive before the next
<code>.bundle_unlock</code> directive has no effect except that it must be
matched by another closing <code>.bundle_unlock</code> so that there is the
same number of <code>.bundle_lock</code> and <code>.bundle_unlock</code> directives.
</p>
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