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090715.1 Ron Brender Add a DW_AT_linkage_name attribute Enhancement Accepted with modifications Ron Brender


Background
----------

A vendor defined attribute DW_AT_MIPS_linkage_name has been in use
for many years by various implementations. This proposal seeks to 
standardize this industry practice within DWARF.

Proposal
--------

1) In Table 1, add an entry for

    DW_AT_linkage_name          Object language name for an entity

2) Add a new Section as follows:

    2.22 Linkage Names

    
    Some language implementations, notably for C++ and similar
    languages, make use of implemntation defined object file
    names that are different from the names of entities as they
    appear in the source. Such names, sometimes known as mangled names, 
    are used in various ways, including: to encode additional information 
    about an entity, to distinguish multiple entities that have the same 
    name, and so on. When an entity has an associated distinct linkage name
    it may sometimes be useful for a producer to include this name
    in the DWARF description of the program to facilitate consumer
    access to and use of object file information about an entity
    and/or information that is encoded in the linkage name itself.
    

    Entities that may reference or be referenced across compilation
    unit boundaries may have a DW_AT_linkage_name attribute whose
    value is a null-terminated string describing the implementation
    defined linkage name associated with the entity.

    If the object file name for an entity is the same as the name in
    the source program, then a linkage name attribute is omitted.

    
    Debugging information entries to which DW_AT_linkage_name may
    apply include: DW_TAG_constant, DW_TAG_entry_point,
    DW_TAG_subprogram and DW_TAG_variable.
    

3)  In Section 3.3.1. General Subroutine and Entry Point Information,
    insert after the second paragraph:

    If the name of a subprogram or entry point described by an entry
    with the tag DW_TAG_subprogram or DW_TAG_entry_point is visible
    outside of its containing compilation unit, it may have a
    DW_AT_linkage_name attribute as described in Section 2.22.

4)  In Section 4.1, Data Object Entries, add a new list item at the
    end:

    14. If the name of a varable or constant is visible outside
        of its enclosing compilation unit, the entity may have a
        DW_AT_linkage_name attribute as described in Section 2.22.

5)  In Figure 20. Attribute Encodings, add

    DW_AT_linkage_name          0x6d            string

6)  In Appendix A, Figure 42, add DW_AT_linkage_name as an applicable
    attribute for

        DW_TAG_constant
        DW_TAG_entry_point
        DW_TAG_subprogram
        DW_TAG_variable

Discussion
----------

An earlier proposal [090503.1] adding linkage name DWARF operators for 
use in location expressions. There was some support for this in
addition to a linkage name attribute, but little support for such
operators alone. Further, operators were generally perceived to be
potentially useful but currently a solution looking for a problem.

This proposal deliberately says nothing about how linkage names are
formed and/or used. That is left for implementations to determine.

Note that linkage name attributes are never required by DWARF, even
in implementations that use mangled names.

-- 

August 11, 2009 -- Accepted with following replacement non-normative
text: "Entities may have a DW_AT__linkage_name whose attribute is a 
null terminated string which describes the implementation defined 
name associated with the entity."


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