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| <a name="Bundle-directives"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Byte.html#Byte" accesskey="n" rel="next">Byte</a>, Previous: <a href="Balign.html#Balign" accesskey="p" rel="prev">Balign</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</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="g_t_002ebundle_005falign_005fmode-abs_002dexpr"></a> |
| <h3 class="section">7.8 <code>.bundle_align_mode <var>abs-expr</var></code></h3> |
| <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’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’s an error if any single |
| instruction’s encoding is longer than the bundle size. |
| </p> |
| <a name="g_t_002ebundle_005flock-and-_002ebundle_005funlock"></a> |
| <h3 class="section">7.9 <code>.bundle_lock</code> and <code>.bundle_unlock</code></h3> |
| <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’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> 0</code><!-- /@w -->. |
| </p> |
| <a name="index-bundle_002dlocked"></a> |
| <p>For some targets, it’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’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. |
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