121 lines
6.1 KiB
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121 lines
6.1 KiB
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<title>Protections - STABS</title>
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<meta name="description" content="STABS">
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<link rel="up" href="Cplusplus.html#Cplusplus" title="Cplusplus">
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<link rel="prev" href="Member-Type-Descriptor.html#Member-Type-Descriptor" title="Member Type Descriptor">
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<link rel="next" href="Method-Modifiers.html#Method-Modifiers" title="Method Modifiers">
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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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<div class="node">
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<a name="Protections"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Method-Modifiers.html#Method-Modifiers">Method Modifiers</a>,
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Previous: <a rel="previous" accesskey="p" href="Member-Type-Descriptor.html#Member-Type-Descriptor">Member Type Descriptor</a>,
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Up: <a rel="up" accesskey="u" href="Cplusplus.html#Cplusplus">Cplusplus</a>
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<hr>
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</div>
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<h3 class="section">8.9 Protections</h3>
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<p>In the simple class definition shown above all member data and
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functions were publicly accessible. The example that follows
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contrasts public, protected and privately accessible fields and shows
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how these protections are encoded in C<tt>++</tt> stabs.
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<p>If the character following the ‘<samp><var>field-name</var><span class="samp">:</span></samp>’ part of the
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string is ‘<samp><span class="samp">/</span></samp>’, then the next character is the visibility. ‘<samp><span class="samp">0</span></samp>’
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means private, ‘<samp><span class="samp">1</span></samp>’ means protected, and ‘<samp><span class="samp">2</span></samp>’ means public.
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Debuggers should ignore visibility characters they do not recognize, and
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assume a reasonable default (such as public) (GDB 4.11 does not, but
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this should be fixed in the next GDB release). If no visibility is
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specified the field is public. The visibility ‘<samp><span class="samp">9</span></samp>’ means that the
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field has been optimized out and is public (there is no way to specify
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an optimized out field with a private or protected visibility).
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Visibility ‘<samp><span class="samp">9</span></samp>’ is not supported by GDB 4.11; this should be fixed
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in the next GDB release.
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<p>The following C<tt>++</tt> source:
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<pre class="example"> class vis {
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private:
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int priv;
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protected:
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char prot;
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public:
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float pub;
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};
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</pre>
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<p class="noindent">generates the following stab:
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<pre class="example"> # <span class="roman">128 is N_LSYM</span>
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.stabs "vis:T19=s12priv:/01,0,32;prot:/12,32,8;pub:12,64,32;;",128,0,0,0
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</pre>
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<p>‘<samp><span class="samp">vis:T19=s12</span></samp>’ indicates that type number 19 is a 12 byte structure
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named <code>vis</code> The <code>priv</code> field has public visibility
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(‘<samp><span class="samp">/0</span></samp>’), type int (‘<samp><span class="samp">1</span></samp>’), and offset and size ‘<samp><span class="samp">,0,32;</span></samp>’.
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The <code>prot</code> field has protected visibility (‘<samp><span class="samp">/1</span></samp>’), type char
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(‘<samp><span class="samp">2</span></samp>’) and offset and size ‘<samp><span class="samp">,32,8;</span></samp>’. The <code>pub</code> field has
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type float (‘<samp><span class="samp">12</span></samp>’), and offset and size ‘<samp><span class="samp">,64,32;</span></samp>’.
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<p>Protections for member functions are signified by one digit embedded in
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the field part of the stab describing the method. The digit is 0 if
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private, 1 if protected and 2 if public. Consider the C<tt>++</tt> class
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definition below:
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<pre class="example"> class all_methods {
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private:
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int priv_meth(int in){return in;};
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protected:
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char protMeth(char in){return in;};
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public:
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float pubMeth(float in){return in;};
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};
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</pre>
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<p>It generates the following stab. The digit in question is to the left
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of an ‘<samp><span class="samp">A</span></samp>’ in each case. Notice also that in this case two symbol
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descriptors apply to the class name struct tag and struct type.
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<pre class="display"> .stabs "class_name:sym_desc(struct tag&type)type_def(21)=
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sym_desc(struct)struct_bytes(1)
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meth_name::type_def(22)=sym_desc(method)returning(int);
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:args(int);protection(private)modifier(normal)virtual(no);
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meth_name::type_def(23)=sym_desc(method)returning(char);
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:args(char);protection(protected)modifier(normal)virtual(no);
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meth_name::type_def(24)=sym_desc(method)returning(float);
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:args(float);protection(public)modifier(normal)virtual(no);;",
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N_LSYM,NIL,NIL,NIL
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</pre>
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<pre class="smallexample"> .stabs "all_methods:Tt21=s1priv_meth::22=##1;:i;0A.;protMeth::23=##2;:c;1A.;
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pubMeth::24=##12;:f;2A.;;",128,0,0,0
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</pre>
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</body></html>
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