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137 lines
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137 lines
6.9 KiB
HTML
15 years ago
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<title>M32R-Directives - Using as</title>
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<meta name="description" content="Using as">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="M32R_002dDependent.html#M32R_002dDependent" title="M32R-Dependent">
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<link rel="prev" href="M32R_002dOpts.html#M32R_002dOpts" title="M32R-Opts">
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<link rel="next" href="M32R_002dWarnings.html#M32R_002dWarnings" title="M32R-Warnings">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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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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under the terms of the GNU Free Documentation License, Version 1.1
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.
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</head>
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<body>
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<div class="node">
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<p>
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<a name="M32R_002dDirectives"></a>Next: <a rel="next" accesskey="n" href="M32R_002dWarnings.html#M32R_002dWarnings">M32R-Warnings</a>,
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Previous: <a rel="previous" accesskey="p" href="M32R_002dOpts.html#M32R_002dOpts">M32R-Opts</a>,
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Up: <a rel="up" accesskey="u" href="M32R_002dDependent.html#M32R_002dDependent">M32R-Dependent</a>
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<hr><br>
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</div>
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<h4 class="subsection">9.19.2 M32R Directives</h4>
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<p><a name="index-directives_002c-M32R-1072"></a><a name="index-M32R-directives-1073"></a>
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The Renease M32R version of <code>as</code> has a few architecture
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specific directives:
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<a name="index-_0040code_007blow_007d-directive_002c-M32R-1074"></a>
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<dl><dt><code>low </code><var>expression</var><dd>The <code>low</code> directive computes the value of its expression and
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places the lower 16-bits of the result into the immediate-field of the
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instruction. For example:
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<pre class="smallexample"> or3 r0, r0, #low(0x12345678) ; compute r0 = r0 | 0x5678
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add3, r0, r0, #low(fred) ; compute r0 = r0 + low 16-bits of address of fred
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</pre>
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<br><dt><code>high </code><var>expression</var><dd><a name="index-_0040code_007bhigh_007d-directive_002c-M32R-1075"></a>The <code>high</code> directive computes the value of its expression and
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places the upper 16-bits of the result into the immediate-field of the
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instruction. For example:
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<pre class="smallexample"> seth r0, #high(0x12345678) ; compute r0 = 0x12340000
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seth, r0, #high(fred) ; compute r0 = upper 16-bits of address of fred
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</pre>
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<br><dt><code>shigh </code><var>expression</var><dd><a name="index-_0040code_007bshigh_007d-directive_002c-M32R-1076"></a>The <code>shigh</code> directive is very similar to the <code>high</code>
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directive. It also computes the value of its expression and places
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the upper 16-bits of the result into the immediate-field of the
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instruction. The difference is that <code>shigh</code> also checks to see
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if the lower 16-bits could be interpreted as a signed number, and if
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so it assumes that a borrow will occur from the upper-16 bits. To
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compensate for this the <code>shigh</code> directive pre-biases the upper
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16 bit value by adding one to it. For example:
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<p>For example:
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<pre class="smallexample"> seth r0, #shigh(0x12345678) ; compute r0 = 0x12340000
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seth r0, #shigh(0x00008000) ; compute r0 = 0x00010000
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</pre>
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<p>In the second example the lower 16-bits are 0x8000. If these are
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treated as a signed value and sign extended to 32-bits then the value
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becomes 0xffff8000. If this value is then added to 0x00010000 then
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the result is 0x00008000.
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<p>This behaviour is to allow for the different semantics of the
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<code>or3</code> and <code>add3</code> instructions. The <code>or3</code> instruction
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treats its 16-bit immediate argument as unsigned whereas the
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<code>add3</code> treats its 16-bit immediate as a signed value. So for
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example:
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<pre class="smallexample"> seth r0, #shigh(0x00008000)
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add3 r0, r0, #low(0x00008000)
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</pre>
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<p>Produces the correct result in r0, whereas:
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<pre class="smallexample"> seth r0, #shigh(0x00008000)
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or3 r0, r0, #low(0x00008000)
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</pre>
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<p>Stores 0xffff8000 into r0.
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<p>Note - the <code>shigh</code> directive does not know where in the assembly
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source code the lower 16-bits of the value are going set, so it cannot
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check to make sure that an <code>or3</code> instruction is being used rather
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than an <code>add3</code> instruction. It is up to the programmer to make
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sure that correct directives are used.
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<p><a name="index-_0040code_007b_002em32r_007d-directive_002c-M32R-1077"></a><br><dt><code>.m32r</code><dd>The directive performs a similar thing as the <em>-m32r</em> command
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line option. It tells the assembler to only accept M32R instructions
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from now on. An instructions from later M32R architectures are
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refused.
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<p><a name="index-_0040code_007b_002em32rx_007d-directive_002c-M32RX-1078"></a><br><dt><code>.m32rx</code><dd>The directive performs a similar thing as the <em>-m32rx</em> command
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line option. It tells the assembler to start accepting the extra
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instructions in the M32RX ISA as well as the ordinary M32R ISA.
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<p><a name="index-_0040code_007b_002em32r2_007d-directive_002c-M32R2-1079"></a><br><dt><code>.m32r2</code><dd>The directive performs a similar thing as the <em>-m32r2</em> command
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line option. It tells the assembler to start accepting the extra
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instructions in the M32R2 ISA as well as the ordinary M32R ISA.
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<p><a name="index-_0040code_007b_002elittle_007d-directive_002c-M32RX-1080"></a><br><dt><code>.little</code><dd>The directive performs a similar thing as the <em>-little</em> command
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line option. It tells the assembler to start producing little-endian
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code and data. This option should be used with care as producing
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mixed-endian binary files is fraught with danger.
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<p><a name="index-_0040code_007b_002ebig_007d-directive_002c-M32RX-1081"></a><br><dt><code>.big</code><dd>The directive performs a similar thing as the <em>-big</em> command
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line option. It tells the assembler to start producing big-endian
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code and data. This option should be used with care as producing
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mixed-endian binary files is fraught with danger.
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</dl>
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</body></html>
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