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

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

Ok, do your thing.


Thx,
Corinna