Re: [PATCH v2] newlib: libm: merge build up a directory

[Mike Frysinger <vapier@gentoo.org>]

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On 21 Feb 2022 12:20, Corinna Vinschen wrote:
> On Feb 16 23:42, Mike Frysinger wrote:
> > Convert all the libm/ subdir makes into the top-level Makefile.  This
> > allows us to build all of libm from the top Makefile without using any
> > recursive make calls.  This is faster and avoids the funky lib.a logic
> > where we unpack subdir archives to repack into a single libm.a.  The
> > machine override logic is maintained though by way of Makefile include
> > ordering, and source file accumulation in libm_a_SOURCES.
> > 
> > One thing to note is that this will require GNU Make because of:
> > 	libm_a_CFLAGS = ... $(libm_a_CFLAGS_$(subst /,_,$(@D)))
> > This was the only way I could find to supporting per-dir compiler
> > settings, and I couldn't find a POSIX compatible way of transforming
> > the variable content.  I don't think this is a big deal as other
> > Makefiles in the tree are using GNU Make-specific syntax, but I call
> > this out as it's the only one so far in the new automake code that
> > I've been writing.
> > 
> > Automake doesn't provide precise control over the output object names
> > (by design).  This is fine by default as we get consistent names in all
> > the subdirs: libm_a-<source>.o.  But this relies on using the same set
> > of compiler flags for all objects.  We currently compile libm/common/
> > with different optimizations than the rest.
> > 
> > If we want to compile objects differently, we can create an intermediate
> > archive with the subset of objects with unique flags, and then add those
> > objects to the main archive.  But Automake will use a different prefix
> > for the objects, and thus we can't rely on ordering to override.
> > 
> > But if we leverage $@, we can turn Automake's CFLAGS into a multiplex
> > on a per-dir (and even per-file if we wanted) basis.  Unfortunately,
> > since $@ contains /, Automake complains it's an invalid name.  While
> > GNU Make supports this, it's a POSIX extension, so Automake flags it.
> > Using $(subst) avoids the Automake warning to get a POSIX compliant
> > name, albeit with a GNU Make extension.
> > ---
> > v2
> > - rebased onto latest tree
> > - fixed a parallel build issue with generated newlib headers & libm objects
> 
> This patch breaks Cygwin.  Unfortunately I didn't try to build myself,
> but only inspected the patch, so I didn't realize the problem.
> 
> First of all, Cygwin takes libm.a from newlib/libm/, not from newlib.
> This is easily fixable.
> 
> However, even after fixing this, we get a link stage error for *all*
> fenv functions:
> 
> ld: x86_64-pc-cygwin/newlib/libm.a(libm_a-fenv.o): in function `fegetenv':
>   newlib/libm/machine/x86_64/../shared_x86/fenv.c:160:
>     multiple definition of `fegetenv';
> x86_64-pc-cygwin/newlib/libm.a(libm_a-fegetenv.o):
>   newlib/libm/fenv/fegetenv.c:65:
>     first defined here
> 
> For some reason, libm.a contains both definitions of the fenv functions,
> the x86_64 definitions from newlib/libm/machine/shared_x86, as well as
> the fallback definitions from newlib/libm/fenv.
> 
> Can you please take a look?

how do you build cygwin ?  i've just been doing w/newlib-cygwin git checkout:
$ ./configure --target=i686-pc-cygwin && make
$ ./configure --target=x86_64-pc-cygwin && make
these are passing for me
-mike

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