Re: [XEN PATCH v4 07/18] build: Introduce documentation for xen Makefiles

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Wed, Apr 08, 2020 at 02:00:43PM +0200, Jan Beulich wrote:
> On 31.03.2020 12:30, Anthony PERARD wrote:
> > This start explainning the variables that can be used in the many
> > Makefiles in xen/.
> > 
> > Most of the document copies and modifies text from Linux v5.4 document
> > linux.git/Documentation/kbuild/makefiles.rst. Modification are mostly
> > to avoid mentioning kbuild. Thus I've added the SPDX tag which was
> > only in index.rst in linux.git.
> > 
> > Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> 
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> with one question:
> 
> > +Compilation flags
> > +-----------------
> > +
> > +    CFLAGS-y and AFLAGS-y
> > +   These two flags apply only to the makefile in which they
> > +   are assigned. They are used for all the normal cc, as and ld
> > +   invocations happening during a recursive build.
> > +
> > +   $(CFLAGS-y) is necessary because the top Makefile owns the
> > +   variable $(XEN_CFLAGS) and uses it for compilation flags for the
> > +   entire tree. And the variable $(CFLAGS) is modified by Config.mk
> > +   which evaluated in every subdirs.
> > +
> > +   CFLAGS-y specifies options for compiling with $(CC).
> > +   AFLAGS-y specifies assembler options.
> 
> Is it perhaps worth mentioning that c_flags and a_flags should
> not be fiddled with by individual Makefile-s?

No, I don't think that's needed. Outside of Rules.mk-s nothing modifies
c_flags, so there isn't a good reason to modify CFLAGS via c_flags
after looking for other examples.
If they do change c_flags anyway, I don't think they would have read
that new documentation.

Thanks,

-- 
Anthony PERARD