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| <h3 class="section">2.9 Assemble in MRI Compatibility Mode: <samp><span class="option">-M</span></samp></h3> |
| |
| <p><a name="index-g_t_002dM-79"></a><a name="index-MRI-compatibility-mode-80"></a>The <samp><span class="option">-M</span></samp> or <samp><span class="option">--mri</span></samp> option selects MRI compatibility mode. This |
| changes the syntax and pseudo-op handling of <samp><span class="command">as</span></samp> to make it |
| compatible with the <code>ASM68K</code> 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 <samp><span class="command">as</span></samp>. |
| |
| <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. <samp><span class="command">as</span></samp> 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 <samp><span class="option">-e</span></samp> 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 <samp><span class="command">as</span></samp> <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 |
| <samp><span class="command">as</span></samp>, 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. <samp><span class="command">as</span></samp> 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. |
| |
| </ul> |
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