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121 lines
4.8 KiB
HTML
121 lines
4.8 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU linker LD
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(SiFive Binutils 2.32.0-2020.04.1)
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version 2.32.
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Copyright (C) 1991-2019 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 1.3
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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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>M68HC11/68HC12 (LD)</title>
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<meta name="description" content="M68HC11/68HC12 (LD)">
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<meta name="keywords" content="M68HC11/68HC12 (LD)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="LD-Index.html#LD-Index" rel="index" title="LD Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Machine-Dependent.html#Machine-Dependent" rel="up" title="Machine Dependent">
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<link href="ARM.html#ARM" rel="next" title="ARM">
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<link href="H8_002f300.html#H8_002f300" rel="prev" title="H8/300">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="M68HC11_002f68HC12"></a>
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<div class="header">
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<p>
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Next: <a href="ARM.html#ARM" accesskey="n" rel="next">ARM</a>, Previous: <a href="H8_002f300.html#H8_002f300" accesskey="p" rel="prev">H8/300</a>, Up: <a href="Machine-Dependent.html#Machine-Dependent" accesskey="u" rel="up">Machine Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="ld-and-the-Motorola-68HC11-and-68HC12-families"></a>
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<h3 class="section">4.2 <code>ld</code> and the Motorola 68HC11 and 68HC12 families</h3>
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<a name="index-M68HC11-and-68HC12-support"></a>
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<a name="Linker-Relaxation"></a>
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<h4 class="subsection">4.2.1 Linker Relaxation</h4>
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<p>For the Motorola 68HC11, <code>ld</code> can perform these global
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optimizations when you specify the ‘<samp>--relax</samp>’ command-line option.
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</p>
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<dl compact="compact">
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<dd><a name="index-relaxing-on-M68HC11"></a>
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</dd>
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<dt><em>relaxing address modes</em></dt>
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<dd><p><code>ld</code> 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>
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<p><code>ld</code> also looks at all 16-bit extended addressing modes and
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transforms them in a direct addressing mode when the address is in
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page 0 (between 0 and 0x0ff).
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</p>
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</dd>
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<dt><em>relaxing gcc instruction group</em></dt>
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<dd><p>When <code>gcc</code> is called with <samp>-mrelax</samp>, it can emit group
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of instructions that the linker can optimize to use a 68HC11 direct
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addressing mode. These instructions consists of <code>bclr</code> or
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<code>bset</code> instructions.
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</p>
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</dd>
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</dl>
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<a name="Trampoline-Generation"></a>
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<h4 class="subsection">4.2.2 Trampoline Generation</h4>
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<a name="index-trampoline-generation-on-M68HC11"></a>
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<a name="index-trampoline-generation-on-M68HC12"></a>
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<p>For 68HC11 and 68HC12, <code>ld</code> can generate trampoline code to
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call a far function using a normal <code>jsr</code> instruction. The linker
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will also change the relocation to some far function to use the
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trampoline address instead of the function address. This is typically the
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case when a pointer to a function is taken. The pointer will in fact
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point to the function trampoline.
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</p>
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</body>
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</html>
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