Question about collecting additional GAS .loc metadata

["Greg Stewart" <gstewart at efn dot org>]

I have a need to collect one additional piece of target-specific
metadata about locations described by the GAS .loc directive and emitted
in the DWARF .debug_line section (ELF64).

Existing directive syntax:
 
  .loc FILENO LINENO [COLUMN] [OPTIONS]

  OPTIONS: [basic_block] [prologue_end] [epilogue_begin]
           [is_stmt VALUE] [isa VALUE]

The metadata could be described using either:

1) an additional target-specific .loc OPTIONS value, e.g. [meta VALUE]

2) a separate target-specific directive, e.g. .loc_meta <value>, which
would then effectively augment the .loc directive currently in effect

The additional location metadata will be stored in a separate object
file section with entries which are related to corresponding .debug_line
section entries.

dwarf2dbg doesn't support target-specific .loc options, nor does it
support the ability to reach into the location entries being produced.
It can see how it would be possible to extend dwarf2dbg to allow for
either or both with TC-style extensions.

I would appreciate any insights as to the preferred strategy for
representing additional target-specific location metadata in the
assembly.

Thanks,
Greg Stewart