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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/stabs/Virtual-Methods.html | |
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diff --git a/share/doc/stabs/Virtual-Methods.html b/share/doc/stabs/Virtual-Methods.html new file mode 100644 index 0000000..ea4b3ea --- /dev/null +++ b/share/doc/stabs/Virtual-Methods.html @@ -0,0 +1,163 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1992-2023 Free Software Foundation, Inc. +Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon, +and David MacKenzie. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, with no Front-Cover Texts, and with no Back-Cover +Texts. A copy of the license is included in the section entitled "GNU +Free Documentation License". --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>STABS: Virtual Methods</title> + +<meta name="description" content="STABS: Virtual Methods"> +<meta name="keywords" content="STABS: Virtual Methods"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Cplusplus.html#Cplusplus" rel="up" title="Cplusplus"> +<link href="Inheritance.html#Inheritance" rel="next" title="Inheritance"> +<link href="Method-Modifiers.html#Method-Modifiers" rel="previous" title="Method Modifiers"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Virtual-Methods"></a> +<div class="header"> +<p> +Next: <a href="Inheritance.html#Inheritance" accesskey="n" rel="next">Inheritance</a>, Previous: <a href="Method-Modifiers.html#Method-Modifiers" accesskey="p" rel="previous">Method Modifiers</a>, Up: <a href="Cplusplus.html#Cplusplus" accesskey="u" rel="up">Cplusplus</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> +</div> +<hr> +<a name="Virtual-Methods-1"></a> +<h3 class="section">8.11 Virtual Methods</h3> + +<p><< The following examples are based on a4.C >> +</p> +<p>The presence of virtual methods in a class definition adds additional +data to the class description. The extra data is appended to the +description of the virtual method and to the end of the class +description. Consider the class definition below: +</p> +<div class="example"> +<pre class="example">class A { +public: + int Adat; + virtual int A_virt (int arg) { return arg; }; +}; +</pre></div> + +<p>This results in the stab below describing class A. It defines a new +type (20) which is an 8 byte structure. The first field of the class +struct is ‘<samp>Adat</samp>’, an integer, starting at structure offset 0 and +occupying 32 bits. +</p> +<p>The second field in the class struct is not explicitly defined by the +C<tt>++</tt> class definition but is implied by the fact that the class +contains a virtual method. This field is the vtable pointer. The +name of the vtable pointer field starts with ‘<samp>$vf</samp>’ and continues with a +type reference to the class it is part of. In this example the type +reference for class A is 20 so the name of its vtable pointer field is +‘<samp>$vf20</samp>’, followed by the usual colon. +</p> +<p>Next there is a type definition for the vtable pointer type (21). +This is in turn defined as a pointer to another new type (22). +</p> +<p>Type 22 is the vtable itself, which is defined as an array, indexed by +a range of integers between 0 and 1, and whose elements are of type +17. Type 17 was the vtable record type defined by the boilerplate C<tt>++</tt> +type definitions, as shown earlier. +</p> +<p>The bit offset of the vtable pointer field is 32. The number of bits +in the field are not specified when the field is a vtable pointer. +</p> +<p>Next is the method definition for the virtual member function <code>A_virt</code>. +Its description starts out using the same format as the non-virtual +member functions described above, except instead of a dot after the +‘<samp>A</samp>’ there is an asterisk, indicating that the function is virtual. +Since is is virtual some addition information is appended to the end +of the method description. +</p> +<p>The first number represents the vtable index of the method. This is a +32 bit unsigned number with the high bit set, followed by a +semi-colon. +</p> +<p>The second number is a type reference to the first base class in the +inheritance hierarchy defining the virtual member function. In this +case the class stab describes a base class so the virtual function is +not overriding any other definition of the method. Therefore the +reference is to the type number of the class that the stab is +describing (20). +</p> +<p>This is followed by three semi-colons. One marks the end of the +current sub-section, one marks the end of the method field, and the +third marks the end of the struct definition. +</p> +<p>For classes containing virtual functions the very last section of the +string part of the stab holds a type reference to the first base +class. This is preceded by ‘<samp>~%</samp>’ and followed by a final semi-colon. +</p> +<div class="display"> +<pre class="display">.stabs "class_name(A):type_def(20)=sym_desc(struct)struct_bytes(8) + field_name(Adat):type_ref(int),bit_offset(0),field_bits(32); + field_name(A virt func ptr):type_def(21)=type_desc(ptr to)type_def(22)= + sym_desc(array)index_type_ref(range of int from 0 to 1); + elem_type_ref(vtbl elem type), + bit_offset(32); + meth_name(A_virt)::typedef(23)=sym_desc(method)returning(int); + :arg_type(int),protection(public)normal(yes)virtual(yes) + vtable_index(1);class_first_defining(A);;;~%first_base(A);", + N_LSYM,NIL,NIL,NIL +</pre></div> + +<div class="example"> +<pre class="example">.stabs "A:t20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32; + A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0 +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Inheritance.html#Inheritance" accesskey="n" rel="next">Inheritance</a>, Previous: <a href="Method-Modifiers.html#Method-Modifiers" accesskey="p" rel="previous">Method Modifiers</a>, Up: <a href="Cplusplus.html#Cplusplus" accesskey="u" rel="up">Cplusplus</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> +</div> + + + +</body> +</html> |