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