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87 lines
3.9 KiB
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87 lines
3.9 KiB
HTML
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<title>M68HC11/68HC12 - Untitled</title>
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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 2.26.
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Copyright (C) 1991-2015 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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<div class="node">
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<a name="M68HC11%2f68HC12"></a>
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<a name="M68HC11_002f68HC12"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="ARM.html#ARM">ARM</a>,
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Previous: <a rel="previous" accesskey="p" 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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</div>
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<h3 class="section">4.3 <samp><span class="command">ld</span></samp> and the Motorola 68HC11 and 68HC12 families</h3>
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<p><a name="index-M68HC11-and-68HC12-support-600"></a>
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<h4 class="subsection">4.3.1 Linker Relaxation</h4>
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<p>For the Motorola 68HC11, <samp><span class="command">ld</span></samp> can perform these global
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optimizations when you specify the ‘<samp><span class="samp">--relax</span></samp>’ command-line option.
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<a name="index-relaxing-on-M68HC11-601"></a>
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<dl><dt><em>relaxing address modes</em><dd><samp><span class="command">ld</span></samp> 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><samp><span class="command">ld</span></samp> 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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<br><dt><em>relaxing gcc instruction group</em><dd>When <samp><span class="command">gcc</span></samp> is called with <samp><span class="option">-mrelax</span></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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</dl>
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<h4 class="subsection">4.3.2 Trampoline Generation</h4>
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<p><a name="index-trampoline-generation-on-M68HC11-602"></a><a name="index-trampoline-generation-on-M68HC12-603"></a>For 68HC11 and 68HC12, <samp><span class="command">ld</span></samp> 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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</body></html>
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