[Dwarf-Discuss] constants updates, minor DWARF standard upgrade?

[Cary Coutant]

For things like new tags, attributes, language codes, etc., we have
occasionally given out assurances that the assigned numbers were safe
to use once discussion was complete and the issue was accepted. In
most cases, it's then OK to use these without bumping the DWARF
version number, since clients are supposed to be able to tolerate
unknown values (although binutils is a notable exception). For
DW_LANG_Go, we did in fact issue such an assurance. (I don't even
think it was necessary to qualify its use under -gstrict-dwarf, since
there's no decent alternative for you to use for Go debug info.)

If DWARF 5 had included nothing new but a few new tags, attributes,
and language codes, we would have had no reason to change the version
number.

New form codes, however, and changes to any of the various compilation
unit headers, always require a new DWARF version number. The consumer
needs to be able to recognize all form codes or it won't be able to
parse the debug info properly, and clearly it needs to understand the
structure of the compilation unit headers for each debug section.

For a long time, in fact, GCC was generating many tags and attributes
from the DWARF-3 spec, while still conforming to the DWARF-2 spec in
terms of header structures and form codes.

-cary