[PATCH] [lld][core] sectionGroup support.

[Shankar Kalpathi Easwaran]

  Nick,

  ELF does use the COMDAT(SHF_COMDAT) type to discard identical sections which are part of group. Section groups on ELF are modeled by using .group sections. The identical sections are grouped by using a signature symbol that is pointed to by the .group section in the input file.

  The reason I would like to have the typeSignature property associated with the group is

  - On ELF, the .group section contains section indices that are part of a group. I think its only ok to say that kindGroupSignature be associated only with the sections that are part of the group. The individual sections that are part of the COMDAT group are converted to atoms and I think those atoms **should not** have //kindGroupSignature //references.
  - The signature symbol needs to be just discarded in the final executable, there is no need to keep them around in the executable/dynamic library
  - The signature symbol can be overridden by a defined symbol or an undefined symbol.
  - At the time of parsing each section by the ELF reader, the ELF reader need not special case that the section was part of which group ?

  Thoughts/Opinions ?

http://llvm-reviews.chandlerc.com/D2710