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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  2. <html>

  3. <!-- Copyright (C) 1992-2020 Free Software Foundation, Inc.

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  8. under the terms of the GNU Free Documentation License, Version 1.3 or

  9. any later version published by the Free Software Foundation; with no

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  11. Texts.  A copy of the license is included in the section entitled "GNU

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  14. <head>

  15. <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

  16. <title>Structures (STABS)</title>

  17. 

  18. <meta name="description" content="Structures (STABS)">

  19. <meta name="keywords" content="Structures (STABS)">

  20. <meta name="resource-type" content="document">

  21. <meta name="distribution" content="global">

  22. <meta name="Generator" content="makeinfo">

  23. <link href="index.html#Top" rel="start" title="Top">

  24. <link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index">

  25. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  26. <link href="Types.html#Types" rel="up" title="Types">

  27. <link href="Typedefs.html#Typedefs" rel="next" title="Typedefs">

  28. <link href="Enumerations.html#Enumerations" rel="prev" title="Enumerations">

  29. <style type="text/css">

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  56. 

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  58. </head>

  59. 

  60. <body lang="en">

  61. <a name="Structures"></a>

  62. <div class="header">

  63. <p>

  64. Next: <a href="Typedefs.html#Typedefs" accesskey="n" rel="next">Typedefs</a>, Previous: <a href="Enumerations.html#Enumerations" accesskey="p" rel="prev">Enumerations</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</a> &nbsp; [<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>

  65. </div>

  66. <hr>

  67. <a name="Structures-1"></a>

  68. <h3 class="section">5.8 Structures</h3>

  69. 

  70. <p>The encoding of structures in stabs can be shown with an example.

  71. </p>

  72. <p>The following source code declares a structure tag and defines an

  73. instance of the structure in global scope. Then a <code>typedef</code> equates the

  74. structure tag with a new type.  Separate stabs are generated for the

  75. structure tag, the structure <code>typedef</code>, and the structure instance.  The

  76. stabs for the tag and the <code>typedef</code> are emitted when the definitions are

  77. encountered.  Since the structure elements are not initialized, the

  78. stab and code for the structure variable itself is located at the end

  79. of the program in the bss section.

  80. </p>

  81. <div class="example">

  82. <pre class="example">struct s_tag {

  83.   int   s_int;

  84.   float s_float;

  85.   char  s_char_vec[8];

  86.   struct s_tag* s_next;

  87. } g_an_s;

  88. 

  89. typedef struct s_tag s_typedef;

  90. </pre></div>

  91. 

  92. <p>The structure tag has an <code>N_LSYM</code> stab type because, like the

  93. enumeration, the symbol has file scope.  Like the enumeration, the

  94. symbol descriptor is &lsquo;<samp>T</samp>&rsquo;, for enumeration, structure, or tag type.

  95. The type descriptor &lsquo;<samp>s</samp>&rsquo; following the &lsquo;<samp>16=</samp>&rsquo; of the type

  96. definition narrows the symbol type to structure.

  97. </p>

  98. <p>Following the &lsquo;<samp>s</samp>&rsquo; type descriptor is the number of bytes the

  99. structure occupies, followed by a description of each structure element.

  100. The structure element descriptions are of the form

  101. &lsquo;<samp><var>name</var>:<var>type</var>, <var>bit offset from the start of the

  102. struct</var>, <var>number of bits in the element</var></samp>&rsquo;.

  103. </p>

  104. <div class="example">

  105. <pre class="example"># <span class="roman">128 is N_LSYM</span>

  106. .stabs &quot;s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;

  107.         s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;&quot;,128,0,0,0

  108. </pre></div>

  109. 

  110. <p>In this example, the first two structure elements are previously defined

  111. types.  For these, the type following the &lsquo;<samp><var>name</var>:</samp>&rsquo; part of the

  112. element description is a simple type reference.  The other two structure

  113. elements are new types.  In this case there is a type definition

  114. embedded after the &lsquo;<samp><var>name</var>:</samp>&rsquo;.  The type definition for the

  115. array element looks just like a type definition for a stand-alone array.

  116. The <code>s_next</code> field is a pointer to the same kind of structure that

  117. the field is an element of.  So the definition of structure type 16

  118. contains a type definition for an element which is a pointer to type 16.

  119. </p>

  120. <p>If a field is a static member (this is a C<tt>++</tt> feature in which a single

  121. variable appears to be a field of every structure of a given type) it

  122. still starts out with the field name, a colon, and the type, but then

  123. instead of a comma, bit position, comma, and bit size, there is a colon

  124. followed by the name of the variable which each such field refers to.

  125. </p>

  126. <p>If the structure has methods (a C<tt>++</tt> feature), they follow the non-method

  127. fields; see <a href="Cplusplus.html#Cplusplus">Cplusplus</a>.

  128. </p>

  129. <hr>

  130. <div class="header">

  131. <p>

  132. Next: <a href="Typedefs.html#Typedefs" accesskey="n" rel="next">Typedefs</a>, Previous: <a href="Enumerations.html#Enumerations" accesskey="p" rel="prev">Enumerations</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</a> &nbsp; [<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>

  133. </div>

  134. 

  135. 

  136. 

  137. </body>

  138. </html>