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175 lines
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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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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<p>
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<a name="M"></a>Next: <a rel="next" accesskey="n" href="MD.html#MD">MD</a>,
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Previous: <a rel="previous" accesskey="p" href="listing.html#listing">listing</a>,
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<hr><br>
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<h3 class="section">2.9 Assemble in MRI Compatibility Mode: <span class="option">-M</span></h3>
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<p><a name="index-_002dM-79"></a><a name="index-MRI-compatibility-mode-80"></a>The <span class="option">-M</span> or <span class="option">--mri</span> option selects MRI compatibility mode. This
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changes the syntax and pseudo-op handling of <span class="command">as</span> to make it
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compatible with the <code>ASM68K</code> or the <code>ASM960</code> (depending upon the
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configured target) assembler from Microtec Research. The exact nature of the
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MRI syntax will not be documented here; see the MRI manuals for more
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information. Note in particular that the handling of macros and macro
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arguments is somewhat different. The purpose of this option is to permit
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assembling existing MRI assembler code using <span class="command">as</span>.
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<p>The MRI compatibility is not complete. Certain operations of the MRI assembler
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depend upon its object file format, and can not be supported using other object
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file formats. Supporting these would require enhancing each object file format
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individually. These are:
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<ul>
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<li>global symbols in common section
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<p>The m68k MRI assembler supports common sections which are merged by the linker.
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Other object file formats do not support this. <span class="command">as</span> handles
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common sections by treating them as a single common symbol. It permits local
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symbols to be defined within a common section, but it can not support global
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symbols, since it has no way to describe them.
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<li>complex relocations
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<p>The MRI assemblers support relocations against a negated section address, and
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relocations which combine the start addresses of two or more sections. These
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are not support by other object file formats.
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<li><code>END</code> pseudo-op specifying start address
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<p>The MRI <code>END</code> pseudo-op permits the specification of a start address.
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This is not supported by other object file formats. The start address may
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instead be specified using the <span class="option">-e</span> option to the linker, or in a linker
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script.
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<li><code>IDNT</code>, <code>.ident</code> and <code>NAME</code> pseudo-ops
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<p>The MRI <code>IDNT</code>, <code>.ident</code> and <code>NAME</code> pseudo-ops assign a module
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name to the output file. This is not supported by other object file formats.
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<li><code>ORG</code> pseudo-op
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<p>The m68k MRI <code>ORG</code> pseudo-op begins an absolute section at a given
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address. This differs from the usual <span class="command">as</span> <code>.org</code> pseudo-op,
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which changes the location within the current section. Absolute sections are
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not supported by other object file formats. The address of a section may be
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assigned within a linker script.
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</ul>
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<p>There are some other features of the MRI assembler which are not supported by
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<span class="command">as</span>, typically either because they are difficult or because they
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seem of little consequence. Some of these may be supported in future releases.
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<ul>
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<li>EBCDIC strings
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<p>EBCDIC strings are not supported.
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<li>packed binary coded decimal
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<p>Packed binary coded decimal is not supported. This means that the <code>DC.P</code>
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and <code>DCB.P</code> pseudo-ops are not supported.
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<li><code>FEQU</code> pseudo-op
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<p>The m68k <code>FEQU</code> pseudo-op is not supported.
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<li><code>NOOBJ</code> pseudo-op
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<p>The m68k <code>NOOBJ</code> pseudo-op is not supported.
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<li><code>OPT</code> branch control options
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<p>The m68k <code>OPT</code> branch control options—<code>B</code>, <code>BRS</code>, <code>BRB</code>,
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<code>BRL</code>, and <code>BRW</code>—are ignored. <span class="command">as</span> automatically
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relaxes all branches, whether forward or backward, to an appropriate size, so
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these options serve no purpose.
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<li><code>OPT</code> list control options
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<p>The following m68k <code>OPT</code> list control options are ignored: <code>C</code>,
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<code>CEX</code>, <code>CL</code>, <code>CRE</code>, <code>E</code>, <code>G</code>, <code>I</code>, <code>M</code>,
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<code>MEX</code>, <code>MC</code>, <code>MD</code>, <code>X</code>.
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<li>other <code>OPT</code> options
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<p>The following m68k <code>OPT</code> options are ignored: <code>NEST</code>, <code>O</code>,
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<code>OLD</code>, <code>OP</code>, <code>P</code>, <code>PCO</code>, <code>PCR</code>, <code>PCS</code>, <code>R</code>.
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<li><code>OPT</code> <code>D</code> option is default
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<p>The m68k <code>OPT</code> <code>D</code> option is the default, unlike the MRI assembler.
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<code>OPT NOD</code> may be used to turn it off.
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<li><code>XREF</code> pseudo-op.
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<p>The m68k <code>XREF</code> pseudo-op is ignored.
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<li><code>.debug</code> pseudo-op
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<p>The i960 <code>.debug</code> pseudo-op is not supported.
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<li><code>.extended</code> pseudo-op
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<p>The i960 <code>.extended</code> pseudo-op is not supported.
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<li><code>.list</code> pseudo-op.
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<p>The various options of the i960 <code>.list</code> pseudo-op are not supported.
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<li><code>.optimize</code> pseudo-op
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<p>The i960 <code>.optimize</code> pseudo-op is not supported.
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<li><code>.output</code> pseudo-op
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<p>The i960 <code>.output</code> pseudo-op is not supported.
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<li><code>.setreal</code> pseudo-op
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<p>The i960 <code>.setreal</code> pseudo-op is not supported.
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</ul>
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</body></html>
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