Re: [PATCH] newlib: remove unused fenv flags

[C Howland <cc1964t@gmail.com>]

On Fri, 11 Feb 2022 at 05:09, Mike Frysinger <vapier@gentoo.org> wrote:

> On 10 Feb 2022 14:18, C Howland wrote:
> >      First, would be if a machine directory can override just some files
> > from the main--as if viewpathed--and this can also apply to the makefile.
> > (Does the machine directory totally replace the main branch directory, or
> > can it be supplemental?  My impression was a viewpath model, which can be
> > supplementary or replace all.)  If I'm wrong about this, no problem, no
> > objection for this specific reason.
>
> assuming "viewpathed" means "VPATH in the makefile", then no, that's not
> how
> newlib works.  that is how glibc works, so maybe you're thinking of that.
> newlib compiles all objects in all subdirs in isolation.  it then assembles
> the final libm.a/libc.a in a specific order (with the machine dir last).
> so
> it adds fenv/*.o to libm.a by basename, then replaces any existing ones
> with
> machine/$arch/*.o.
>

Yes, I meant as in VPATH in a makefile with individual file granularity.
So, yes, I was thinking not the right thing for newlib, sorry for
conflating Newlib with other things.

>
> >      The second is if the main branch is intended to also be a template
> for
> > new machine directories.  The C part of it definitely is, but the
> makefile
> > does not necessarily fall into that category.  So I'll turn that into a
> > question:  if the main branch makefile does not serve as a template for
> the
> > machine directories, where would that be?  That is, while these arguments
> > are superfluous in the main dir,  should they remain in comments as an
> aid
> > to machine developers, in the same manner in which the source code is
> > annotated?  (It's not so much these specific arguments, themselves, but
> > having an example how ones like this would be added.  These particular
> ones
> > are reasonable for serving that purpose, however.)  The real makefile
> seems
> > the best place for this.  We could have Makefile.template, or something
> > along those lines, but the real one is forced to be valid by being used,
> > while maintaining a separate template would be additional maintenance
> work.
> >      So if I'm wrong about the viewpathing model, a suggestion:  rather
> > than deleting the lines, comment them out and add some comment text
> > suitable for a template.  If you're amenable to this approach and would
> > like, I (or possibly Joel if he's interested) could contribute suggested
> > comments for you to use.
>
> this isn't specific to fenv/.  you can make this argument against any of
> the subdirs.
>
> even then, the use of -fbuiltin & -fno-math-errno kind of seem like the
> opposite of what you're arguing.  -fno-math-errno shouldn't be used in
> general as it is an optimization that can break correctness wrt IEEE
> standards.  -fbuiltin probably shouldn't be applied to entire subdirs
> without strict review since it allows the compiler to rewrite calls
> that assume C library behavior, but the C library might be violating
> those assumptions specifically as part of its implementation.
> -mike
>

OK, neither you nor Joel think templating for the makefile to be of much
use, that makes a majority in comments so far and I'll go along.  (Since
fenv is special and tricky I think we would be better off with better
instructions for this one particularly, as it would encourage/help people
to add new targets.)
I agree that these specific compiler options do need care taken.  But
that's part of the reason they're good examples for the fenv environment,
as that's a tricky subject that needs special attention and might need
things like them.  But at the same time I agree that they are also for the
same reason potentially dangerous to suggest.
(By the way, off the specific topic, but thanks for spending all the time
on cleaning up the build process.)
Craig