Re: Per-machine additions to CFLAGS-rtld.c being overridden.

[Roland McGrath <roland at hack dot frob dot com>]

There are several layers here.

* Using per-file (or per-directory) *FLAGS settings is always the worst
  option.  Not only is it obscure and easily overlooked, it doesn't get
  tracked as a dependency to recompile things as needed.  We should avoid
  it whenever possible.

  If it's used for things like -D switches there is just no excuse.	
  That can be done with wrapper source files in sysdeps instead.

  When it's used for code-generation options, it can't really be avoided at
  the moment.  One day the GCC pragma/attribute features for embedding such
  options directly in the sources will be complete and we'll require
  building libc with a GCC new enough to support all that.  But that will
  be a long time off.

* The reason subdir Makefiles do 'include ../Rules' earlyish rather than
  last is so that the Makefile's own targets can use variables defined by
  the infrastructure code.  In addition to $(objpfx) and the like, some
  places need to use make conditionals based on variables set by the common
  stuff.  It probably doesn't occur that such conditionals are used to
  decide about setting CFLAGS-* variables.  But it's just an overly tweaky
  requirement that all variables be set before the include when pretty much
  all targets/rules need to come after it.

* The real problem here is that both sysdeps makefile fragments and main
  makefiles are both setting the same variables.  It just makes confusion
  and subtle errors like this far too likely.  Originally that never
  happened.  That's why we have things like sysdep-CFLAGS.  I think we
  should fix the general problem by establishing a new rule that sysdeps
  makefiles shall not touch such variables.  Without any generic changes,
  they could already do:

	sysdeps-CFLAGS += $(sysdep-CFLAGS-$(<F))
	sysdeps-CFLAGS-foo.c = -mblah

  But since there already numerous examples, we might as well just change
  CFLAGS in Makeconfig to use $(sysdep-CFLAGS-$(<F)) after the existing
  generic per-file variables.


Thanks,
Roland