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83 lines
4.2 KiB
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83 lines
4.2 KiB
HTML
<html lang="en">
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<head>
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<title>H8/300 - Untitled</title>
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<meta name="description" content="Untitled">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Machine-Dependent.html#Machine-Dependent" title="Machine Dependent">
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<link rel="next" href="i960.html#i960" title="i960">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU linker LD
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(GNU Binutils)
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version 2.19.
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
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2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.1
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.-->
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<style type="text/css"><!--
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</head>
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<body>
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<div class="node">
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<p>
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<a name="H8_002f300"></a>Next: <a rel="next" accesskey="n" href="i960.html#i960">i960</a>,
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Up: <a rel="up" accesskey="u" href="Machine-Dependent.html#Machine-Dependent">Machine Dependent</a>
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<hr><br>
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</div>
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<h3 class="section">4.1 <span class="command">ld</span> and the H8/300</h3>
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<p><a name="index-H8_002f300-support-522"></a>For the H8/300, <span class="command">ld</span> can perform these global optimizations when
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you specify the <span class="samp">--relax</span> command-line option.
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<a name="index-relaxing-on-H8_002f300-523"></a>
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<dl><dt><em>relaxing address modes</em><dd><span class="command">ld</span> finds all <code>jsr</code> and <code>jmp</code> instructions whose
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targets are within eight bits, and turns them into eight-bit
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program-counter relative <code>bsr</code> and <code>bra</code> instructions,
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respectively.
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<p><a name="index-synthesizing-on-H8_002f300-524"></a><br><dt><em>synthesizing instructions</em><dd><!-- FIXME: specifically mov.b, or any mov instructions really? -->
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<span class="command">ld</span> finds all <code>mov.b</code> instructions which use the
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sixteen-bit absolute address form, but refer to the top
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page of memory, and changes them to use the eight-bit address form.
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(That is: the linker turns <span class="samp">mov.b </span><code>@</code><var>aa</var><span class="samp">:16</span> into
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<span class="samp">mov.b </span><code>@</code><var>aa</var><span class="samp">:8</span> whenever the address <var>aa</var> is in the
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top page of memory).
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<br><dt><em>bit manipulation instructions</em><dd><span class="command">ld</span> finds all bit manipulation instructions like <code>band, bclr,
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biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor</code>
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which use 32 bit and 16 bit absolute address form, but refer to the top
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page of memory, and changes them to use the 8 bit address form.
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(That is: the linker turns <span class="samp">bset #xx:3,</span><code>@</code><var>aa</var><span class="samp">:32</span> into
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<span class="samp">bset #xx:3,</span><code>@</code><var>aa</var><span class="samp">:8</span> whenever the address <var>aa</var> is in
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the top page of memory).
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<br><dt><em>system control instructions</em><dd><span class="command">ld</span> finds all <code>ldc.w, stc.w</code> instructions which use the
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32 bit absolute address form, but refer to the top page of memory, and
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changes them to use 16 bit address form.
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(That is: the linker turns <span class="samp">ldc.w </span><code>@</code><var>aa</var><span class="samp">:32,ccr</span> into
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<span class="samp">ldc.w </span><code>@</code><var>aa</var><span class="samp">:16,ccr</span> whenever the address <var>aa</var> is in
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the top page of memory).
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</dl>
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</body></html>
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