RFC Adding a section group flag of 0

[Nick Clifton <nickc at redhat dot com>]

Hi Guys,

  Currently the ELF standard for section groups requires that the first word 
  of data in the group section be a flag, with only certain values recognised:

    The following flags are currently defined:
    Figure 4-13: Section Group Flags

    Name 		Value
    GRP_COMDAT 		0x1
    GRP_MASKOS 		0x0ff00000
    GRP_MASKPROC 	0xf0000000

    [...]

  I would like to propose adding a new value to this list.  A value of 0.
  This value would indicate that the section group has no special processing
  semantics, and that the contents of the group, unless discarded via garbage
  collection, should be linked as normal.

  This matches the current behaviour of the bfd and gold linkers, and it would
  also help to resolve a problem for the lld linker:

https://reviews.llvm.org/D56437

  This is not a theoretical problem, as binaries containing section groups with
  a flag value of zero already exist:

https://bugzilla.redhat.com/show_bug.cgi?id=1658942

  The maintainers of lld have stated, quite reasonably, that they do not want to
  add support for an unofficial flag value.  Hence I would like to make the value
  official.

  What do people think ?

Cheers
  Nick