toolchain/share/doc/stabs/Protections.html

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