jankratochvil added a comment.

In https://reviews.llvm.org/D32167#1062614, @clayborg wrote:

> Found the DWZ stuff:
>  http://www.dwarfstd.org/ShowIssue.php?issue=120604.1&type=open

BTW the current DWZ tool <https://sourceware.org/git/?p=dwz.git> supports only 
DWARF-4 and the DWZ tags are non-standard GNU extensions.  Therefore 
`DW_FORM_GNU_ref_alt` in existing DWZ files is `DW_FORM_ref_alt` in the 
proposal you found. I am not aware of any real documentation for this DWARF-4 
GNU extension. But DWARF-5 further modified the proposal so it became 
`DW_FORM_ref_sup4`+`DW_FORM_ref_sup8` in the DWARF-5 standard.

My DWZ-for-LLDB patchset implements the DWARF-4 non-standard GNU extensions as 
it is used in RHEL-7 (and possibly RHEL-8, not sure yet) which will be 
supported at least till 2024. It is also present in all recent Fedoras. 
Currently the DWZ tool has not yet been ported to DWARF-5, Mark Wielaard from 
Red Hat plans to do so.


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