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    SubjectRe: [RFC PATCH 05/33] Makefile support to build Xen subarch
    Andrew Morton wrote:
    > @@ -99,6 +103,7 @@ drivers-$(CONFIG_PM) += arch/i386/powe
    >
    > CFLAGS += $(mflags-y)
    > AFLAGS += $(mflags-y)
    > +CPPFLAGS += $(mflags-y)
    >
    > This change affects _all_ subarchitectures (by potentially altering their
    > CPPFLAGS) and it's rather a mystery why one subarch needs the -Ifoo in its
    > CPPFLAGS whereas all the others do not.
    >

    The reason is that arch-i386/kernel/vmlinux.lds.S is run through CPP,
    and it includes asm/thread_info.h and asm/page.h, which end up including
    "mach_page.h" (which this patch series introduces). There is a version
    in both mach-default/mach_page.h and mach-xen/mach_page.h, so the -I is
    necessary for non-Xen sub-arches as well.

    I guess the conservative approach would be to only add this -I for the
    vmlinux.lds target, assuming there are no later compile problems. On
    the flip-side, would you want C and Asm code getting a different set of
    includes from "manually" preprocessed-files? I would think you'd want
    either defines/includes at all, or to have them identical.

    The CPPFLAGS assignment also appears to make the previous two lines
    redundant, since a_flags and c_flags (which is what actually gets used
    for compilation) end up having CPPFLAGS incorporated into them.

    J

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