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(stabs.info)Unions

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Unions
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     union u_tag {
       int  u_int;
       float u_float;
       char* u_char;
     } an_u;

   This code generates a stab for a union tag and a stab for a union
variable.  Both use the `N_LSYM' stab type.  If a union variable is
scoped locally to the procedure in which it is defined, its stab is
located immediately preceding the `N_LBRAC' for the procedure's block
start.

   The stab for the union tag, however, is located preceding the code
for the procedure in which it is defined.  The stab type is `N_LSYM'.
This would seem to imply that the union type is file scope, like the
struct type `s_tag'.  This is not true.  The contents and position of
the stab for `u_type' do not convey any information about its procedure
local scope.

     # 128 is N_LSYM
     .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
            128,0,0,0

   The symbol descriptor `T', following the `name:' means that the stab
describes an enumeration, structure, or union tag.  The type descriptor
`u', following the `23=' of the type definition, narrows it down to a
union type definition.  Following the `u' is the number of bytes in the
union.  After that is a list of union element descriptions.  Their
format is NAME:TYPE, BIT OFFSET INTO THE UNION, NUMBER OF BYTES FOR THE
ELEMENT;.

   The stab for the union variable is:

     .stabs "an_u:23",128,0,0,-20     # 128 is N_LSYM

   `-20' specifies where the variable is stored (Note: Stack
Variables).