106 lines
6.0 KiB
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106 lines
6.0 KiB
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<title>Constants - STABS</title>
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<link rel="prev" href="Program-Structure.html#Program-Structure" title="Program Structure">
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<link rel="next" href="Variables.html#Variables" title="Variables">
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Copyright (C) 1992-2019 Free Software Foundation, Inc.
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Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
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and David MacKenzie.
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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 or
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<a name="Constants"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Variables.html#Variables">Variables</a>,
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Previous: <a rel="previous" accesskey="p" href="Program-Structure.html#Program-Structure">Program Structure</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<hr>
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</div>
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<h2 class="chapter">3 Constants</h2>
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<p>The ‘<samp><span class="samp">c</span></samp>’ symbol descriptor indicates that this stab represents a
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constant. This symbol descriptor is an exception to the general rule
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that symbol descriptors are followed by type information. Instead, it
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is followed by ‘<samp><span class="samp">=</span></samp>’ and one of the following:
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<dl>
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<dt><code>b </code><var>value</var><dd>Boolean constant. <var>value</var> is a numeric value; I assume it is 0 for
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false or 1 for true.
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<br><dt><code>c </code><var>value</var><dd>Character constant. <var>value</var> is the numeric value of the constant.
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<br><dt><code>e </code><var>type-information</var><code> , </code><var>value</var><dd>Constant whose value can be represented as integral.
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<var>type-information</var> is the type of the constant, as it would appear
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after a symbol descriptor (see <a href="String-Field.html#String-Field">String Field</a>). <var>value</var> is the
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numeric value of the constant. GDB 4.9 does not actually get the right
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value if <var>value</var> does not fit in a host <code>int</code>, but it does not
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do anything violent, and future debuggers could be extended to accept
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integers of any size (whether unsigned or not). This constant type is
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usually documented as being only for enumeration constants, but GDB has
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never imposed that restriction; I don't know about other debuggers.
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<br><dt><code>i </code><var>value</var><dd>Integer constant. <var>value</var> is the numeric value. The type is some
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sort of generic integer type (for GDB, a host <code>int</code>); to specify
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the type explicitly, use ‘<samp><span class="samp">e</span></samp>’ instead.
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<br><dt><code>r </code><var>value</var><dd>Real constant. <var>value</var> is the real value, which can be ‘<samp><span class="samp">INF</span></samp>’
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(optionally preceded by a sign) for infinity, ‘<samp><span class="samp">QNAN</span></samp>’ for a quiet
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NaN (not-a-number), or ‘<samp><span class="samp">SNAN</span></samp>’ for a signalling NaN. If it is a
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normal number the format is that accepted by the C library function
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<code>atof</code>.
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<br><dt><code>s </code><var>string</var><dd>String constant. <var>string</var> is a string enclosed in either ‘<samp><span class="samp">'</span></samp>’
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(in which case ‘<samp><span class="samp">'</span></samp>’ characters within the string are represented as
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‘<samp><span class="samp">\'</span></samp>’ or ‘<samp><span class="samp">"</span></samp>’ (in which case ‘<samp><span class="samp">"</span></samp>’ characters within the
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string are represented as ‘<samp><span class="samp">\"</span></samp>’).
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<br><dt><code>S </code><var>type-information</var><code> , </code><var>elements</var><code> , </code><var>bits</var><code> , </code><var>pattern</var><dd>Set constant. <var>type-information</var> is the type of the constant, as it
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would appear after a symbol descriptor (see <a href="String-Field.html#String-Field">String Field</a>).
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<var>elements</var> is the number of elements in the set (does this means
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how many bits of <var>pattern</var> are actually used, which would be
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redundant with the type, or perhaps the number of bits set in
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<var>pattern</var>? I don't get it), <var>bits</var> is the number of bits in the
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constant (meaning it specifies the length of <var>pattern</var>, I think),
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and <var>pattern</var> is a hexadecimal representation of the set. AIX
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documentation refers to a limit of 32 bytes, but I see no reason why
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this limit should exist. This form could probably be used for arbitrary
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constants, not just sets; the only catch is that <var>pattern</var> should be
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understood to be target, not host, byte order and format.
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</dl>
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<p>The boolean, character, string, and set constants are not supported by
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GDB 4.9, but it ignores them. GDB 4.8 and earlier gave an error
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message and refused to read symbols from the file containing the
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constants.
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<p>The above information is followed by ‘<samp><span class="samp">;</span></samp>’.
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</body></html>
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