Re: [PATCH] newlib: remove unused fenv flags

Mike Frysinger <[email protected]> Fri, 11 Feb 2022 05:09:54 -0500
Newsgroups	gmane.comp.lib.newlib
Message-ID	<YgY18sCOk3wQZ/4y@vapier>
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.

>      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
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