| <html lang="en"> |
| <head> |
| <title>MIPS Symbol Sizes - Using as</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="Using as"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="MIPS_002dDependent.html#MIPS_002dDependent" title="MIPS-Dependent"> |
| <link rel="prev" href="MIPS-Macros.html#MIPS-Macros" title="MIPS Macros"> |
| <link rel="next" href="MIPS-Small-Data.html#MIPS-Small-Data" title="MIPS Small Data"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU Assembler "as". |
| |
| Copyright (C) 1991-2019 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 |
| or any later version published by the Free Software Foundation; |
| with no Invariant Sections, with no Front-Cover Texts, and with no |
| Back-Cover Texts. A copy of the license is included in the |
| section entitled ``GNU Free Documentation License''. |
| |
| --> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="MIPS-Symbol-Sizes"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="MIPS-Small-Data.html#MIPS-Small-Data">MIPS Small Data</a>, |
| Previous: <a rel="previous" accesskey="p" href="MIPS-Macros.html#MIPS-Macros">MIPS Macros</a>, |
| Up: <a rel="up" accesskey="u" href="MIPS_002dDependent.html#MIPS_002dDependent">MIPS-Dependent</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">9.27.3 Directives to override the size of symbols</h4> |
| |
| <p><a name="index-g_t_0040code_007b_002eset-sym32_007d-1576"></a><a name="index-g_t_0040code_007b_002eset-nosym32_007d-1577"></a>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><span class="samp">dla $4,sym</span></samp>’ is usually: |
| |
| <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> |
| <p>whereas the 32-bit expansion is simply: |
| |
| <pre class="smallexample"> lui $4,%hi(sym) |
| daddiu $4,$4,%lo(sym) |
| </pre> |
| <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>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><span class="samp"> + </span><var>offset</var></samp>’ |
| have 32-bit values. For example: |
| |
| <pre class="smallexample"> .set sym32 |
| dla $4,sym |
| lw $4,sym+16 |
| sw $4,sym+0x8000($4) |
| </pre> |
| <p>will cause the assembler to treat ‘<samp><span class="samp">sym</span></samp>’, <code>sym+16</code> and |
| <code>sym+0x8000</code> as 32-bit values. The handling of non-symbolic |
| addresses is not affected. |
| |
| <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><span class="option">-msym32</span></samp> and |
| <samp><span class="option">-mno-sym32</span></samp>. |
| |
| <p>These options and directives are always accepted, but at present, |
| they have no effect for anything other than n64. |
| |
| </body></html> |
| |