xen/build: use new $(c_flags) and $(a_flags) instead of $(CFLAGS)

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).

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 dd40177c1b ("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>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/Rules.mk

@@ -57,7 +57,6 @@ CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 $(call cc-option-add,CFLAGS,CC,-Wvla)
 CFLAGS += -pipe -D__XEN__ -include $(BASEDIR)/include/xen/config.h
 CFLAGS-$(CONFIG_DEBUG_INFO) += -g
-CFLAGS += '-D__OBJECT_FILE__="$@"'
 
 ifneq ($(CONFIG_CC_IS_CLANG),y)
 # Clang doesn't understand this command line argument, and doesn't appear to
@@ -70,9 +69,6 @@ AFLAGS += -D__ASSEMBLY__
 
 ALL_OBJS := $(ALL_OBJS-y)
 
-# Get gcc to generate the dependencies for us.
-CFLAGS-y += -MMD -MP -MF $(@D)/.$(@F).d
-
 CFLAGS += $(CFLAGS-y)
 # allow extra CFLAGS externally via EXTRA_CFLAGS_XEN_CORE
 CFLAGS += $(EXTRA_CFLAGS_XEN_CORE)
@@ -146,9 +142,12 @@ endif
 # Always build obj-bin files as binary even if they come from C source. 
 $(obj-bin-y): CFLAGS := $(filter-out -flto,$(CFLAGS))
 
+c_flags = -MMD -MP -MF $(@D)/.$(@F).d $(CFLAGS) '-D__OBJECT_FILE__="$@"'
+a_flags = -MMD -MP -MF $(@D)/.$(@F).d $(AFLAGS)
+
 built_in.o: $(obj-y) $(extra-y)
 ifeq ($(obj-y),)
-	$(CC) $(CFLAGS) -c -x c /dev/null -o $@
+	$(CC) $(c_flags) -c -x c /dev/null -o $@
 else
 ifeq ($(CONFIG_LTO),y)
 	$(LD_LTO) -r -o $@ $(filter-out $(extra-y),$^)
@@ -159,7 +158,7 @@ endif
 
 built_in_bin.o: $(obj-bin-y) $(extra-y)
 ifeq ($(obj-bin-y),)
-	$(CC) $(AFLAGS) -c -x assembler /dev/null -o $@
+	$(CC) $(a_flags) -c -x assembler /dev/null -o $@
 else
 	$(LD) $(LDFLAGS) -r -o $@ $(filter-out $(extra-y),$^)
 endif
@@ -178,7 +177,7 @@ SRCPATH := $(patsubst $(BASEDIR)/%,%,$(CURDIR))
 
 %.o: %.c Makefile
 ifeq ($(CONFIG_ENFORCE_UNIQUE_SYMBOLS),y)
-	$(CC) $(CFLAGS) -c $< -o $(@D)/.$(@F).tmp -MQ $@
+	$(CC) $(c_flags) -c $< -o $(@D)/.$(@F).tmp -MQ $@
 ifeq ($(CONFIG_CC_IS_CLANG),y)
 	$(OBJCOPY) --redefine-sym $<=$(SRCPATH)/$< $(@D)/.$(@F).tmp $@
 else
@@ -186,11 +185,11 @@ else
 endif
 	rm -f $(@D)/.$(@F).tmp
 else
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(c_flags) -c $< -o $@
 endif
 
 %.o: %.S Makefile
-	$(CC) $(AFLAGS) -c $< -o $@
+	$(CC) $(a_flags) -c $< -o $@
 
 $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): %.init.o: %.o Makefile
 	$(OBJDUMP) -h $< | sed -n '/[0-9]/{s,00*,0,g;p;}' | while read idx name sz rest; do \
@@ -205,12 +204,12 @@ $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): %.init.o: %.o Makefile
 	$(OBJCOPY) $(foreach s,$(SPECIAL_DATA_SECTIONS),--rename-section .$(s)=.init.$(s)) $< $@
 
 %.i: %.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(CFLAGS)) $< -o $@
+	$(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) $< -o $@
 
 %.s: %.c Makefile
-	$(CC) $(filter-out -Wa$(comma)%,$(CFLAGS)) -S $< -o $@
+	$(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -S $< -o $@
 
 %.s: %.S Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(AFLAGS)) $< -o $@
+	$(CPP) $(filter-out -Wa$(comma)%,$(a_flags)) $< -o $@
 
 -include $(DEPS_INCLUDE)

xen/arch/arm/Makefile

@@ -120,10 +120,10 @@ $(TARGET)-syms: prelink.o xen.lds
 	rm -f $(@D)/.$(@F).[0-9]*
 
 asm-offsets.s: $(TARGET_SUBARCH)/asm-offsets.c
-	$(CC) $(filter-out -flto,$(CFLAGS)) -S -o $@ $<
+	$(CC) $(filter-out -flto,$(c_flags)) -S -o $@ $<
 
 xen.lds: xen.lds.S
-	$(CC) -P -E -Ui386 $(AFLAGS) -o $@ $<
+	$(CC) -P -E -Ui386 $(a_flags) -o $@ $<
 	sed -e 's/xen\.lds\.o:/xen\.lds:/g' <.xen.lds.d >.xen.lds.d.new
 	mv -f .xen.lds.d.new .xen.lds.d
 

xen/arch/x86/Makefile

@@ -168,7 +168,7 @@ EFI_LDFLAGS += --major-os-version=2 --minor-os-version=0
 EFI_LDFLAGS += --major-subsystem-version=2 --minor-subsystem-version=0
 
 # Check if the compiler supports the MS ABI.
-export XEN_BUILD_EFI := $(shell $(CC) $(filter-out $(CFLAGS-y) .%.d,$(CFLAGS)) -c efi/check.c -o efi/check.o 2>/dev/null && echo y)
+export XEN_BUILD_EFI := $(shell $(CC) $(CFLAGS) -c efi/check.c -o efi/check.o 2>/dev/null && echo y)
 # Check if the linker supports PE.
 XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(shell $(LD) -mi386pep --subsystem=10 -o efi/check.efi efi/check.o 2>/dev/null && echo y))
 CFLAGS-$(XEN_BUILD_EFI) += -DXEN_BUILD_EFI
@@ -223,7 +223,7 @@ efi/boot.init.o efi/runtime.o efi/compat.o efi/buildid.o efi/relocs-dummy.o: $(B
 efi/boot.init.o efi/runtime.o efi/compat.o efi/buildid.o efi/relocs-dummy.o: ;
 
 asm-offsets.s: $(TARGET_SUBARCH)/asm-offsets.c $(BASEDIR)/include/asm-x86/asm-macros.h
-	$(CC) $(filter-out -Wa$(comma)% -flto,$(CFLAGS)) -S -o $@ $<
+	$(CC) $(filter-out -Wa$(comma)% -flto,$(c_flags)) -S -o $@ $<
 
 asm-macros.i: CFLAGS += -D__ASSEMBLY__ -P
 
@@ -240,7 +240,7 @@ $(BASEDIR)/include/asm-x86/asm-macros.h: asm-macros.i Makefile
 
 efi.lds: AFLAGS += -DEFI
 xen.lds efi.lds: xen.lds.S
-	$(CC) -P -E -Ui386 $(filter-out -Wa$(comma)%,$(AFLAGS)) -o $@ $<
+	$(CC) -P -E -Ui386 $(filter-out -Wa$(comma)%,$(a_flags)) -o $@ $<
 	sed -e 's/.*\.lds\.o:/$(@F):/g' <.$(@F).d >.$(@F).d.new
 	mv -f .$(@F).d.new .$(@F).d
 

xen/arch/x86/mm/Makefile

@@ -12,10 +12,10 @@ obj-$(CONFIG_HVM) += p2m-ept.o p2m-pod.o
 obj-y += paging.o
 
 guest_walk_%.o: guest_walk.c Makefile
-	$(CC) $(CFLAGS) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CC) $(c_flags) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%.i: guest_walk.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(CFLAGS)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%.s: guest_walk.c Makefile
-	$(CC) $(filter-out -Wa$(comma)%,$(CFLAGS)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@
+	$(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@

xen/arch/x86/mm/hap/Makefile

@@ -6,10 +6,10 @@ obj-y += nested_hap.o
 obj-y += nested_ept.o
 
 guest_walk_%level.o: guest_walk.c Makefile
-	$(CC) $(CFLAGS) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CC) $(c_flags) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%level.i: guest_walk.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(CFLAGS)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%level.s: guest_walk.c Makefile
-	$(CC) $(filter-out -Wa$(comma)%,$(CFLAGS)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@
+	$(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@

xen/arch/x86/mm/shadow/Makefile

@@ -7,10 +7,10 @@ obj-y += none.o
 endif
 
 guest_%.o: multi.c Makefile
-	$(CC) $(CFLAGS) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CC) $(c_flags) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_%.i: multi.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(CFLAGS)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_%.s: multi.c Makefile
-	$(CC) $(filter-out -Wa$(comma)%,$(CFLAGS)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@
+	$(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@

xen/include/Makefile

@@ -64,7 +64,7 @@ compat/%.h: compat/%.i Makefile $(BASEDIR)/tools/compat-build-header.py
 	mv -f $@.new $@
 
 compat/%.i: compat/%.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)% -M% %.d -include %/include/xen/config.h,$(CFLAGS)) $(cppflags-y) -o $@ $<
+	$(CPP) $(filter-out -Wa$(comma)% -include %/include/xen/config.h,$(CFLAGS)) $(cppflags-y) -o $@ $<
 
 compat/%.c: public/%.h xlat.lst Makefile $(BASEDIR)/tools/compat-build-source.py
 	mkdir -p $(@D)