mingw/info/stabs/Unions.html

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  12 Node:<a name="Unions">Unions</a>,
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  18
  19 <h3 class="section">Unions</h3>
  20
  21 <pre class="example">     union u_tag {
  22        int  u_int;
  23        float u_float;
  24        char* u_char;
  25      } an_u;
  26      </pre>
  27
  28    <p>This code generates a stab for a union tag and a stab for a union
  29 variable.  Both use the <code>N_LSYM</code> stab type.  If a union variable is
  30 scoped locally to the procedure in which it is defined, its stab is
  31 located immediately preceding the <code>N_LBRAC</code> for the procedure's block
  32 start.
  33
  34    <p>The stab for the union tag, however, is located preceding the code for
  35 the procedure in which it is defined.  The stab type is <code>N_LSYM</code>.  This
  36 would seem to imply that the union type is file scope, like the struct
  37 type <code>s_tag</code>.  This is not true.  The contents and position of the stab
  38 for <code>u_type</code> do not convey any information about its procedure local
  39 scope.
  40
  41 <pre class="smallexample">     # 128 is N_LSYM
  42      .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
  43             128,0,0,0
  44      </pre>
  45
  46    <p>The symbol descriptor <code>T</code>, following the <code>name:</code> means that
  47 the stab describes an enumeration, structure, or union tag.  The type
  48 descriptor <code>u</code>, following the <code>23=</code> of the type definition,
  49 narrows it down to a union type definition.  Following the <code>u</code> is
  50 the number of bytes in the union.  After that is a list of union element
  51 descriptions.  Their format is <var>name:type, bit offset into the
  52 union, number of bytes for the element;</var>.
  53
  54    <p>The stab for the union variable is:
  55
  56 <pre class="example">     .stabs "an_u:23",128,0,0,-20     # 128 is N_LSYM
  57      </pre>
  58
  59    <p><code>-20</code> specifies where the variable is stored (see <a href="Stack-Variables.html#Stack%20Variables">Stack Variables</a>).
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