[PATCH/RFC] Generic OS ABI handling for gdbarch

[Jason R Thorpe <thorpej at wasabisystems dot com>]

I started working on generic OS ABI handling for GDB today, lifting from
the various duplicated bits of code in several targets.

There are two pieces to the generic code:

	* OS ABI handlers.  These are basically the same as the OS ABI
	  handlers that exist on a per-target basis, but when they're
	  registered, you now specify a bfd_architecture.  Only one
	  OS ABI can exist per bfd_architecture.

	* OS ABI "sniffers".  These peek at a BFD with a given
	  bfd_architecture/bfd_flavour and determine which OS ABI
	  is correct for that BFD.  Multiple sniffers can exist for
	  a given bfd_architecture/bfd_flavour, e.g. one to sniff out
	  NetBSD a.out, one for FreeBSD a.out, etc.  If a sniffer
	  registers w/ bfd_architecture of "unknown", it can sniff
	  files of any architecture for its flavour.

	  There is a generic ELF sniffer that uses EI_OSABI and note
	  sections.  (This is an example of an arch == "unknown"
	  sniffer.)

	  The first sniffer to return other than GDB_OSABI_UNKNOWN
	  wins, so sniffers should be careful to only claim BFDs
	  they're sure about.

Tomorrow I'll make the Alpha and SH targets use the generic OS ABI
framework as examples.

Comments appreciated.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>

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