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