On Sat, Oct 03, 2015 at 05:17:53PM +0900, Oleg Endo wrote:
> On Sat, 2015-10-03 at 00:50 -0400, Rich Felker wrote:
>
> > I have -mfdpic in the self-specs when FDPIC_DEFAULT is defined, so I
> > think only the positive form is needed.
>
> Having positive and negative forms for options makes sense. It usually
> costs nothing because anyway the compiler internally supports both and
> it allows special-casing if one of them is the default, which can be
> useful for testing.
What I'm saying is that the self-specs approach to FDPIC_DEFAULT has
the compiler driver adding -mfdpic to its own command line (via
%{!mno-fdpic:-mfdpic}) when FDPIC_DEFAULT is defined. This allows
other specs simply to test %{mfdpic:...} rather than having complex
separate forms depending on whether FDPIC_DEFAULT is defined. The
negative form is of course supported too (and suppresses the self-spec
addition of -mfdpic).
I'm not sure if this approach is acceptable upstream in gcc. I like it
a lot better because it isolates this kind of logic as described above
rather than having it spread out all over the place in error-prone
ways. I had a several-line patch for default-pie support that worked
via self-specs too; the one that was actually committed to gcc was
hugely invasive across many files including most targets...
Rich
