<html lang="en"> <head> <title>H8/300 - Untitled</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="Untitled"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Machine-Dependent.html#Machine-Dependent" title="Machine Dependent"> <link rel="next" href="i960.html#i960" title="i960"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <!-- This file documents the GNU linker LD (GNU Binutils) version 2.26. Copyright (C) 1991-2015 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="H8%2f300"></a> <a name="H8_002f300"></a> <p> Next: <a rel="next" accesskey="n" href="i960.html#i960">i960</a>, Up: <a rel="up" accesskey="u" href="Machine-Dependent.html#Machine-Dependent">Machine Dependent</a> <hr> </div> <h3 class="section">4.1 <samp><span class="command">ld</span></samp> and the H8/300</h3> <p><a name="index-H8_002f300-support-594"></a>For the H8/300, <samp><span class="command">ld</span></samp> can perform these global optimizations when you specify the ‘<samp><span class="samp">--relax</span></samp>’ command-line option. <a name="index-relaxing-on-H8_002f300-595"></a> <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 targets are within eight bits, and turns them into eight-bit program-counter relative <code>bsr</code> and <code>bra</code> instructions, respectively. <p><a name="index-synthesizing-on-H8_002f300-596"></a><br><dt><em>synthesizing instructions</em><dd><!-- FIXME: specifically mov.b, or any mov instructions really? -> mov.b only, at least on H8, H8H, H8S --> <samp><span class="command">ld</span></samp> finds all <code>mov.b</code> instructions which use the sixteen-bit absolute address form, but refer to the top page of memory, and changes them to use the eight-bit address form. (That is: the linker turns ‘<samp><span class="samp">mov.b </span><code>@</code><var>aa</var><span class="samp">:16</span></samp>’ into ‘<samp><span class="samp">mov.b </span><code>@</code><var>aa</var><span class="samp">:8</span></samp>’ whenever the address <var>aa</var> is in the top page of memory). <p><samp><span class="command">ld</span></samp> finds all <code>mov</code> instructions which use the register indirect with 32-bit displacement addressing mode, but use a small displacement inside 16-bit displacement range, and changes them to use the 16-bit displacement form. (That is: the linker turns ‘<samp><span class="samp">mov.b </span><code>@</code><var>d</var><span class="samp">:32,ERx</span></samp>’ into ‘<samp><span class="samp">mov.b </span><code>@</code><var>d</var><span class="samp">:16,ERx</span></samp>’ whenever the displacement <var>d</var> is in the 16 bit signed integer range. Only implemented in ELF-format ld). <br><dt><em>bit manipulation instructions</em><dd><samp><span class="command">ld</span></samp> finds all bit manipulation instructions like <code>band, bclr, biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor</code> which use 32 bit and 16 bit absolute address form, but refer to the top page of memory, and changes them to use the 8 bit address form. (That is: the linker turns ‘<samp><span class="samp">bset #xx:3,</span><code>@</code><var>aa</var><span class="samp">:32</span></samp>’ into ‘<samp><span class="samp">bset #xx:3,</span><code>@</code><var>aa</var><span class="samp">:8</span></samp>’ whenever the address <var>aa</var> is in the top page of memory). <br><dt><em>system control instructions</em><dd><samp><span class="command">ld</span></samp> finds all <code>ldc.w, stc.w</code> instructions which use the 32 bit absolute address form, but refer to the top page of memory, and changes them to use 16 bit address form. (That is: the linker turns ‘<samp><span class="samp">ldc.w </span><code>@</code><var>aa</var><span class="samp">:32,ccr</span></samp>’ into ‘<samp><span class="samp">ldc.w </span><code>@</code><var>aa</var><span class="samp">:16,ccr</span></samp>’ whenever the address <var>aa</var> is in the top page of memory). </dl> </body></html>