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| <title>Using as: MIPS Symbol Sizes</title> |
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| <a name="MIPS-Symbol-Sizes"></a> |
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| Next: <a href="MIPS-Small-Data.html#MIPS-Small-Data" accesskey="n" rel="next">MIPS Small Data</a>, Previous: <a href="MIPS-Macros.html#MIPS-Macros" accesskey="p" rel="prev">MIPS Macros</a>, Up: <a href="MIPS_002dDependent.html#MIPS_002dDependent" accesskey="u" rel="up">MIPS-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="Directives-to-override-the-size-of-symbols"></a> |
| <h4 class="subsection">9.27.3 Directives to override the size of symbols</h4> |
| |
| <a name="index-_002eset-sym32"></a> |
| <a name="index-_002eset-nosym32"></a> |
| <p>The n64 ABI allows symbols to have any 64-bit value. Although this |
| provides a great deal of flexibility, it means that some macros have |
| much longer expansions than their 32-bit counterparts. For example, |
| the non-PIC expansion of ‘<samp>dla $4,sym</samp>’ is usually: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">lui $4,%highest(sym) |
| lui $1,%hi(sym) |
| daddiu $4,$4,%higher(sym) |
| daddiu $1,$1,%lo(sym) |
| dsll32 $4,$4,0 |
| daddu $4,$4,$1 |
| </pre></div> |
| |
| <p>whereas the 32-bit expansion is simply: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">lui $4,%hi(sym) |
| daddiu $4,$4,%lo(sym) |
| </pre></div> |
| |
| <p>n64 code is sometimes constructed in such a way that all symbolic |
| constants are known to have 32-bit values, and in such cases, it’s |
| preferable to use the 32-bit expansion instead of the 64-bit |
| expansion. |
| </p> |
| <p>You can use the <code>.set sym32</code> directive to tell the assembler |
| that, from this point on, all expressions of the form |
| ‘<samp><var>symbol</var></samp>’ or ‘<samp><var>symbol</var> + <var>offset</var></samp>’ |
| have 32-bit values. For example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">.set sym32 |
| dla $4,sym |
| lw $4,sym+16 |
| sw $4,sym+0x8000($4) |
| </pre></div> |
| |
| <p>will cause the assembler to treat ‘<samp>sym</samp>’, <code>sym+16</code> and |
| <code>sym+0x8000</code> as 32-bit values. The handling of non-symbolic |
| addresses is not affected. |
| </p> |
| <p>The directive <code>.set nosym32</code> ends a <code>.set sym32</code> block and |
| reverts to the normal behavior. It is also possible to change the |
| symbol size using the command-line options <samp>-msym32</samp> and |
| <samp>-mno-sym32</samp>. |
| </p> |
| <p>These options and directives are always accepted, but at present, |
| they have no effect for anything other than n64. |
| </p> |
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