Re: [Xen-devel] [XEN PATCH v3 14/23] xen/build: use new $(c_flags) and $(a_flags) instead of $(CFLAGS)

From: Anthony PERARD <anthony.perard@citrix.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
	Jan Beulich <jbeulich@suse.com>,
	Anthony PERARD <anthony.perard@gmail.com>,
	xen-devel@lists.xenproject.org,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [XEN PATCH v3 14/23] xen/build: use new $(c_flags) and $(a_flags) instead of $(CFLAGS)
Date: Tue, 10 Mar 2020 17:55:35 +0000	[thread overview]
Message-ID: <20200310175535.GG2152@perard.uk.xensource.com> (raw)
In-Reply-To: <20200227102238.GM24458@Air-de-Roger.citrite.net>

On Thu, Feb 27, 2020 at 11:22:38AM +0100, Roger Pau Monné wrote:
> On Wed, Feb 26, 2020 at 11:33:46AM +0000, Anthony PERARD wrote:
> > From: Anthony PERARD <anthony.perard@gmail.com>
> > 
> > In a later patch ("xen/build: have the root Makefile generates the
> > CFLAGS), we want to generate the CFLAGS in xen/Makefile, then export
> > it and have Rules.mk use a CFLAGS from the environment variables. That
> > changes the flavor of the CFLAGS and flags intended for one target
> > (like -D__OBJECT_FILE__ and -M%) gets propagated and duplicated. So we
> > start by moving such flags out of $(CFLAGS) and into $(c_flags) which
> > is to be modified by only Rules.mk.
> > 
> > __OBJECT_FILE__ is only used by arch/x86/mm/*.c files, so having it in
> > $(c_flags) is enough, we don't need it in $(a_flags).
> 
> This seem to be used only by source files that are build multiple
> times with different parameters in order to generate different object
> files.
> 
> Is there any harm in having it also in the assembler flags? (in case
> we require such usage in the future)

Not really any harm, no, but that can be done later when needed I think.

> Or maybe we could even limit __OBJECT_FILE__ to mm/ files that require
> it only?

That's a possibility, yes. I'll be adding flags to those specific files
anyway (GUEST_PAGING_LEVELS, done in a later patch), I could add
__OBJECT_FILE__ to the list.

> > 
> > For include/Makefile and as-insn we can keep using CFLAGS, but since
> > it doesn't have -M* flags anymore there is no need to filter them out.
> > 
> > The XEN_BUILD_EFI tests in arch/x86/Makefile was filtering out
> > CFLAGS-y, but according to dd40177c1bc8 ("x86-64/EFI: add CFLAGS to
> > check compile"), it was done to filter out -MF. CFLAGS doesn't
> > have those flags anymore, so no filtering is needed.
> > 
> > This is inspired by the way Kbuild generates CFLAGS for each targets.
> > 
> > Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks,

-- 
Anthony PERARD

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