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

On Wed, Feb 26, 2020 at 11:33:46AM +0000, Anthony PERARD wrote:
> From: Anthony PERARD <anthony.perard@xxxxxxxxx>
> 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

Is there any harm in having it also in the assembler flags? (in case
we require such usage in the future)

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

> 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@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

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