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118 lines
6.6 KiB
HTML
<html lang="en">
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<head>
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<title>Options-i960 - Using as</title>
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<link rel="up" href="i960_002dDependent.html#i960_002dDependent" title="i960-Dependent">
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<link rel="next" href="Floating-Point_002di960.html#Floating-Point_002di960" title="Floating Point-i960">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2015 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 1.3
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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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<div class="node">
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<a name="Options-i960"></a>
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<a name="Options_002di960"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Floating-Point_002di960.html#Floating-Point_002di960">Floating Point-i960</a>,
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Up: <a rel="up" accesskey="u" href="i960_002dDependent.html#i960_002dDependent">i960-Dependent</a>
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<hr>
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</div>
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<h4 class="subsection">9.17.1 i960 Command-line Options</h4>
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<p><a name="index-i960-options-1178"></a><a name="index-options_002c-i960-1179"></a>
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<a name="index-i960-architecture-options-1180"></a>
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<a name="index-architecture-options_002c-i960-1181"></a>
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<a name="index-g_t_0040code_007b_002dA_007d-options_002c-i960-1182"></a>
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<dl><dt><code>-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC</code><dd>Select the 80960 architecture. Instructions or features not supported
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by the selected architecture cause fatal errors.
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<p>‘<samp><span class="samp">-ACA</span></samp>’ is equivalent to ‘<samp><span class="samp">-ACA_A</span></samp>’; ‘<samp><span class="samp">-AKC</span></samp>’ is equivalent to
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‘<samp><span class="samp">-AMC</span></samp>’. Synonyms are provided for compatibility with other tools.
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<p>If you do not specify any of these options, <code>as</code> generates code
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for any instruction or feature that is supported by <em>some</em> version of the
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960 (even if this means mixing architectures!). In principle,
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<code>as</code> attempts to deduce the minimal sufficient processor type if
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none is specified; depending on the object code format, the processor type may
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be recorded in the object file. If it is critical that the <code>as</code>
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output match a specific architecture, specify that architecture explicitly.
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<p><a name="index-g_t_0040code_007b_002db_007d-option_002c-i960-1183"></a><a name="index-branch-recording_002c-i960-1184"></a><a name="index-i960-branch-recording-1185"></a><br><dt><code>-b</code><dd>Add code to collect information about conditional branches taken, for
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later optimization using branch prediction bits. (The conditional branch
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instructions have branch prediction bits in the CA, CB, and CC
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architectures.) If <var>BR</var> represents a conditional branch instruction,
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the following represents the code generated by the assembler when
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‘<samp><span class="samp">-b</span></samp>’ is specified:
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<pre class="smallexample"> call <var>increment routine</var>
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.word 0 # pre-counter
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Label: <var>BR</var>
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call <var>increment routine</var>
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.word 0 # post-counter
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</pre>
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<p>The counter following a branch records the number of times that branch
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was <em>not</em> taken; the difference between the two counters is the
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number of times the branch <em>was</em> taken.
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<p><a name="index-g_t_0040code_007bgbr960_007d_002c-i960-postprocessor-1186"></a><a name="index-branch-statistics-table_002c-i960-1187"></a>A table of every such <code>Label</code> is also generated, so that the
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external postprocessor <code>gbr960</code> (supplied by Intel) can locate all
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the counters. This table is always labeled ‘<samp><span class="samp">__BRANCH_TABLE__</span></samp>’;
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this is a local symbol to permit collecting statistics for many separate
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object files. The table is word aligned, and begins with a two-word
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header. The first word, initialized to 0, is used in maintaining linked
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lists of branch tables. The second word is a count of the number of
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entries in the table, which follow immediately: each is a word, pointing
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to one of the labels illustrated above.
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<!-- TEXI2ROFF-KILL -->
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<!-- END TEXI2ROFF-KILL -->
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<p>The first word of the header is used to locate multiple branch tables,
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since each object file may contain one. Normally the links are
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maintained with a call to an initialization routine, placed at the
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beginning of each function in the file. The <span class="sc">gnu</span> C compiler
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generates these calls automatically when you give it a ‘<samp><span class="samp">-b</span></samp>’ option.
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For further details, see the documentation of ‘<samp><span class="samp">gbr960</span></samp>’.
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<p><a name="index-g_t_0040code_007b_002dno_002drelax_007d-option_002c-i960-1188"></a><br><dt><code>-no-relax</code><dd>Normally, Compare-and-Branch instructions with targets that require
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displacements greater than 13 bits (or that have external targets) are
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replaced with the corresponding compare (or ‘<samp><span class="samp">chkbit</span></samp>’) and branch
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instructions. You can use the ‘<samp><span class="samp">-no-relax</span></samp>’ option to specify that
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<code>as</code> should generate errors instead, if the target displacement
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is larger than 13 bits.
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<p>This option does not affect the Compare-and-Jump instructions; the code
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emitted for them is <em>always</em> adjusted when necessary (depending on
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displacement size), regardless of whether you use ‘<samp><span class="samp">-no-relax</span></samp>’.
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</dl>
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</body></html>
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