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| <h3 class="section">5.10 Unions</h3> |
| |
| <pre class="example"> union u_tag { |
| int u_int; |
| float u_float; |
| char* u_char; |
| } an_u; |
| </pre> |
| <p>This code generates a stab for a union tag and a stab for a union |
| variable. Both use the <code>N_LSYM</code> stab type. If a union variable is |
| scoped locally to the procedure in which it is defined, its stab is |
| located immediately preceding the <code>N_LBRAC</code> for the procedure's block |
| start. |
| |
| <p>The stab for the union tag, however, is located preceding the code for |
| the procedure in which it is defined. The stab type is <code>N_LSYM</code>. This |
| would seem to imply that the union type is file scope, like the struct |
| type <code>s_tag</code>. This is not true. The contents and position of the stab |
| for <code>u_type</code> do not convey any information about its procedure local |
| scope. |
| |
| <!-- FIXME: phony line break. Can probably be fixed by using an example --> |
| <!-- with fewer fields. --> |
| <pre class="smallexample"> # <span class="roman">128 is N_LSYM</span> |
| .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;", |
| 128,0,0,0 |
| </pre> |
| <p>The symbol descriptor ‘<samp><span class="samp">T</span></samp>’, following the ‘<samp><span class="samp">name:</span></samp>’ means that |
| the stab describes an enumeration, structure, or union tag. The type |
| descriptor ‘<samp><span class="samp">u</span></samp>’, following the ‘<samp><span class="samp">23=</span></samp>’ of the type definition, |
| narrows it down to a union type definition. Following the ‘<samp><span class="samp">u</span></samp>’ is |
| the number of bytes in the union. After that is a list of union element |
| descriptions. Their format is ‘<samp><var>name</var><span class="samp">:</span><var>type</var><span class="samp">, </span><var>bit |
| offset into the union</var><span class="samp">, </span><var>number of bytes for the element</var><span class="samp">;</span></samp>’. |
| |
| <p>The stab for the union variable is: |
| |
| <pre class="example"> .stabs "an_u:23",128,0,0,-20 # <span class="roman">128 is N_LSYM</span> |
| </pre> |
| <p>‘<samp><span class="samp">-20</span></samp>’ specifies where the variable is stored (see <a href="Stack-Variables.html#Stack-Variables">Stack Variables</a>). |
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