160 lines
7.3 KiB
HTML
160 lines
7.3 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1992-2017 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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any later version published by the Free Software Foundation; with no
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Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled "GNU
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Free Documentation License". -->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>STABS: Arrays</title>
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<meta name="description" content="STABS: Arrays">
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<meta name="keywords" content="STABS: Arrays">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Types.html#Types" rel="up" title="Types">
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<link href="Strings.html#Strings" rel="next" title="Strings">
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<link href="Subranges.html#Subranges" rel="prev" title="Subranges">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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div.display {margin-left: 3.2em}
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pre.format {font-family: inherit}
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span.roman {font-family:serif; font-weight:normal}
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-->
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Arrays"></a>
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<div class="header">
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<p>
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Next: <a href="Strings.html#Strings" accesskey="n" rel="next">Strings</a>, Previous: <a href="Subranges.html#Subranges" accesskey="p" rel="prev">Subranges</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Array-Types"></a>
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<h3 class="section">5.5 Array Types</h3>
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<p>Arrays use the ‘<samp>a</samp>’ type descriptor. Following the type descriptor
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is the type of the index and the type of the array elements. If the
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index type is a range type, it ends in a semicolon; otherwise
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(for example, if it is a type reference), there does not
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appear to be any way to tell where the types are separated. In an
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effort to clean up this mess, IBM documents the two types as being
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separated by a semicolon, and a range type as not ending in a semicolon
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(but this is not right for range types which are not array indexes,
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see <a href="Subranges.html#Subranges">Subranges</a>). I think probably the best solution is to specify
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that a semicolon ends a range type, and that the index type and element
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type of an array are separated by a semicolon, but that if the index
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type is a range type, the extra semicolon can be omitted. GDB (at least
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through version 4.9) doesn’t support any kind of index type other than a
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range anyway; I’m not sure about dbx.
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</p>
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<p>It is well established, and widely used, that the type of the index,
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unlike most types found in the stabs, is merely a type definition, not
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type information (see <a href="String-Field.html#String-Field">String Field</a>) (that is, it need not start with
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‘<samp><var>type-number</var>=</samp>’ if it is defining a new type). According to a
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comment in GDB, this is also true of the type of the array elements; it
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gives ‘<samp>ar1;1;10;ar1;1;10;4</samp>’ as a legitimate way to express a two
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dimensional array. According to AIX documentation, the element type
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must be type information. GDB accepts either.
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</p>
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<p>The type of the index is often a range type, expressed as the type
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descriptor ‘<samp>r</samp>’ and some parameters. It defines the size of the
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array. In the example below, the range ‘<samp>r1;0;2;</samp>’ defines an index
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type which is a subrange of type 1 (integer), with a lower bound of 0
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and an upper bound of 2. This defines the valid range of subscripts of
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a three-element C array.
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</p>
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<p>For example, the definition:
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</p>
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<div class="example">
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<pre class="example">char char_vec[3] = {'a','b','c'};
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</pre></div>
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<p>produces the output:
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</p>
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<div class="example">
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<pre class="example">.stabs "char_vec:G19=ar1;0;2;2",32,0,0,0
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.global _char_vec
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.align 4
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_char_vec:
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.byte 97
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.byte 98
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.byte 99
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</pre></div>
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<p>If an array is <em>packed</em>, the elements are spaced more
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closely than normal, saving memory at the expense of speed. For
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example, an array of 3-byte objects might, if unpacked, have each
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element aligned on a 4-byte boundary, but if packed, have no padding.
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One way to specify that something is packed is with type attributes
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(see <a href="String-Field.html#String-Field">String Field</a>). In the case of arrays, another is to use the
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‘<samp>P</samp>’ type descriptor instead of ‘<samp>a</samp>’. Other than specifying a
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packed array, ‘<samp>P</samp>’ is identical to ‘<samp>a</samp>’.
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</p>
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<p>An open array is represented by the ‘<samp>A</samp>’ type descriptor followed by
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type information specifying the type of the array elements.
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</p>
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<p>An N-dimensional dynamic array is represented by
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</p>
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<div class="example">
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<pre class="example">D <var>dimensions</var> ; <var>type-information</var>
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</pre></div>
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<p><var>dimensions</var> is the number of dimensions; <var>type-information</var>
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specifies the type of the array elements.
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</p>
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<p>A subarray of an N-dimensional array is represented by
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</p>
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<div class="example">
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<pre class="example">E <var>dimensions</var> ; <var>type-information</var>
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</pre></div>
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<p><var>dimensions</var> is the number of dimensions; <var>type-information</var>
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specifies the type of the array elements.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Strings.html#Strings" accesskey="n" rel="next">Strings</a>, Previous: <a href="Subranges.html#Subranges" accesskey="p" rel="prev">Subranges</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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