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<title>STABS: Builtin Type Descriptors</title>
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<a name="Builtin-Type-Descriptors"></a>
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<div class="header">
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<p>
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Next: <a href="Negative-Type-Numbers.html#Negative-Type-Numbers" accesskey="n" rel="next">Negative Type Numbers</a>, Previous: <a href="Traditional-Builtin-Types.html#Traditional-Builtin-Types" accesskey="p" rel="previous">Traditional Builtin Types</a>, Up: <a href="Builtin-Types.html#Builtin-Types" accesskey="u" rel="up">Builtin 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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<hr>
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<a name="Defining-Builtin-Types-Using-Builtin-Type-Descriptors"></a>
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<h4 class="subsection">5.1.2 Defining Builtin Types Using Builtin Type Descriptors</h4>
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<p>This is the method used by Sun’s <code>acc</code> for defining builtin types.
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These are the type descriptors to define builtin types:
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</p>
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<dl compact="compact">
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<dt><code>b <var>signed</var> <var>char-flag</var> <var>width</var> ; <var>offset</var> ; <var>nbits</var> ;</code></dt>
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<dd><p>Define an integral type. <var>signed</var> is ‘<samp>u</samp>’ for unsigned or
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‘<samp>s</samp>’ for signed. <var>char-flag</var> is ‘<samp>c</samp>’ which indicates this
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is a character type, or is omitted. I assume this is to distinguish an
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integral type from a character type of the same size, for example it
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might make sense to set it for the C type <code>wchar_t</code> so the debugger
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can print such variables differently (Solaris does not do this). Sun
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sets it on the C types <code>signed char</code> and <code>unsigned char</code> which
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arguably is wrong. <var>width</var> and <var>offset</var> appear to be for small
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objects stored in larger ones, for example a <code>short</code> in an
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<code>int</code> register. <var>width</var> is normally the number of bytes in the
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type. <var>offset</var> seems to always be zero. <var>nbits</var> is the number
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of bits in the type.
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</p>
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<p>Note that type descriptor ‘<samp>b</samp>’ used for builtin types conflicts with
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its use for Pascal space types (see <a href="Miscellaneous-Types.html#Miscellaneous-Types">Miscellaneous Types</a>); they can
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be distinguished because the character following the type descriptor
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will be a digit, ‘<samp>(</samp>’, or ‘<samp>-</samp>’ for a Pascal space type, or
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‘<samp>u</samp>’ or ‘<samp>s</samp>’ for a builtin type.
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</p>
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</dd>
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<dt><code>w</code></dt>
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<dd><p>Documented by AIX to define a wide character type, but their compiler
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actually uses negative type numbers (see <a href="Negative-Type-Numbers.html#Negative-Type-Numbers">Negative Type Numbers</a>).
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</p>
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</dd>
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<dt><code>R <var>fp-type</var> ; <var>bytes</var> ;</code></dt>
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<dd><p>Define a floating point type. <var>fp-type</var> has one of the following values:
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</p>
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<dl compact="compact">
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<dt><code>1 (NF_SINGLE)</code></dt>
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<dd><p>IEEE 32-bit (single precision) floating point format.
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</p>
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</dd>
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<dt><code>2 (NF_DOUBLE)</code></dt>
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<dd><p>IEEE 64-bit (double precision) floating point format.
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</p>
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</dd>
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<dt><code>3 (NF_COMPLEX)</code></dt>
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<dt><code>4 (NF_COMPLEX16)</code></dt>
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<dt><code>5 (NF_COMPLEX32)</code></dt>
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<dd><p>These are for complex numbers. A comment in the GDB source describes
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them as Fortran <code>complex</code>, <code>double complex</code>, and
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<code>complex*16</code>, respectively, but what does that mean? (i.e., Single
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precision? Double precision?).
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</p>
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</dd>
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<dt><code>6 (NF_LDOUBLE)</code></dt>
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<dd><p>Long double. This should probably only be used for Sun format
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<code>long double</code>, and new codes should be used for other floating
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point formats (<code>NF_DOUBLE</code> can be used if a <code>long double</code> is
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really just an IEEE double, of course).
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</p></dd>
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</dl>
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<p><var>bytes</var> is the number of bytes occupied by the type. This allows a
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debugger to perform some operations with the type even if it doesn’t
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understand <var>fp-type</var>.
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</p>
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</dd>
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<dt><code>g <var>type-information</var> ; <var>nbits</var></code></dt>
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<dd><p>Documented by AIX to define a floating type, but their compiler actually
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uses negative type numbers (see <a href="Negative-Type-Numbers.html#Negative-Type-Numbers">Negative Type Numbers</a>).
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</p>
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</dd>
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<dt><code>c <var>type-information</var> ; <var>nbits</var></code></dt>
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<dd><p>Documented by AIX to define a complex type, but their compiler actually
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uses negative type numbers (see <a href="Negative-Type-Numbers.html#Negative-Type-Numbers">Negative Type Numbers</a>).
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</p></dd>
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</dl>
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<p>The C <code>void</code> type is defined as a signed integral type 0 bits long:
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</p><div class="example">
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<pre class="example">.stabs "void:t19=bs0;0;0",128,0,0,0
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</pre></div>
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<p>The Solaris compiler seems to omit the trailing semicolon in this case.
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Getting sloppy in this way is not a swift move because if a type is
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embedded in a more complex expression it is necessary to be able to tell
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where it ends.
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</p>
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<p>I’m not sure how a boolean type is represented.
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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="Negative-Type-Numbers.html#Negative-Type-Numbers" accesskey="n" rel="next">Negative Type Numbers</a>, Previous: <a href="Traditional-Builtin-Types.html#Traditional-Builtin-Types" accesskey="p" rel="previous">Traditional Builtin Types</a>, Up: <a href="Builtin-Types.html#Builtin-Types" accesskey="u" rel="up">Builtin 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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