Mangled Typedef names in GNU 4.1.2 DWARF data?

[Michael Eager]

Ron Louzon wrote:
> The GNU 4.1.2 C++ compiler is mangling typedef names to the point that they are not retrievable from the DWARF data.
> 
> For example, the type BASE_UNION is defined as
> 
> typedef union
> {
>    char ch;
>    int iVal;
>    long IVal;
> } BASE_UNION;

This is an anonymous union which is typedef'ed to BASE_UNION.

> 
> The GNU 4.1.2 compiler generates the following DWARF data for this type
> 
> <1><1279>: Abbrev Number: 35 (DW_TAG_union_type)
>   <127a>     DW_AT_sibling     : <12a8>	
>   <127e>     DW_AT_name        : $_4	
>   <1282>     DW_AT_byte_size   : 4	
>   <1283>     DW_AT_decl_file   : 35	
>   <1284>     DW_AT_decl_line   : 29	

This doesn't look correct.  The union has no name, so DW_AT_name should
not be present or should be null.  From the DWARF v.3 spec:

   2.15 Identifier Names

   Any debugging information entry representing a program entity that has been
   given a name may have a DW_AT_name attribute, whose value is a string
   representing the name as it appears in the source program. A debugging
   information entry containing no name attribute, or containing a name attribute
   whose value consists of a name containing a single null byte, represents a
   program entity for which no name was given in the source.

>  <2><1285>: Abbrev Number: 36 (DW_TAG_member)
>   <1286>     DW_AT_name        : ch	
>   <1289>     DW_AT_decl_file   : 35	
>   <128a>     DW_AT_decl_line   : 30	
>   <128b>     DW_AT_type        : <c0d>	
>  <2><128f>: Abbrev Number: 36 (DW_TAG_member)
>   <1290>     DW_AT_name        : iVal	
>   <1295>     DW_AT_decl_file   : 35	
>   <1296>     DW_AT_decl_line   : 31	
>   <1297>     DW_AT_type        : <b7f>	
>  <2><129b>: Abbrev Number: 36 (DW_TAG_member)
>   <129c>     DW_AT_name        : IVal	
>   <12a1>     DW_AT_decl_file   : 35	
>   <12a2>     DW_AT_decl_line   : 32	
>   <12a3>     DW_AT_type        : <b86>	
> 
> Notice that the union name has been changed to "$_4" in DIE <1279>.
> 
> The GNU 3.4.4 compiler generates the following DWARF data from the same source code:
> 
>  <1><11d0>: Abbrev Number: 27 (DW_TAG_union_type)
>      DW_AT_sibling     : <123f>	
>      DW_AT_name        : (indirect string, offset: 0x6e): BASE_UNION	
>      DW_AT_byte_size   : 4	
>      DW_AT_decl_file   : 3	
>      DW_AT_decl_line   : 29	

This is similarly incorrect.  The union has no name.


> Why is GNU 4.1.2 generating the mangled type name and how do I correct this to generate the real type name?

A better question might by why there is no DW_TAG_typedef
DIE which looks like

    DW_TAG_typedef
      DW_AT_name:   BASE_UNION
      DW_AT_type:   <1279>

BTW gcc-4.3.2 generates

   DW_AT_name: <anonymous union>

which is also incorrect.



-- 
Michael Eager	 eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077