Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---

Notes:
    v7:
    - also filter -flto
    - and convert "asm-offsets.s" and "xen/x86/%.lds" to use cpp_flags as
      well.
    
    v6:
    - switch to a macro as suggested
      which allows to be used with both a_flags and c_flags
    
    v5:
    - new patch

 xen/Makefile                    | 2 +-
 xen/Rules.mk                    | 7 +++++--
 xen/arch/x86/Makefile           | 2 +-
 xen/arch/x86/mm/Makefile        | 2 +-
 xen/arch/x86/mm/hap/Makefile    | 2 +-
 xen/arch/x86/mm/shadow/Makefile | 2 +-
 6 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/xen/Makefile b/xen/Makefile
index 94e837182615..4ceb02d37441 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -410,7 +410,7 @@ include/xen/compile.h: include/xen/compile.h.in .banner
 	@mv -f $@.new $@
 
 asm-offsets.s: arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.c
-	$(CC) $(filter-out -Wa$(comma)% -flto,$(c_flags)) -S -g0 -o $@.new -MQ $@ $<
+	$(CC) $(call cpp_flags,$(c_flags)) -S -g0 -o $@.new -MQ $@ $<
 	$(call move-if-changed,$@.new,$@)
 
 include/asm-$(TARGET_ARCH)/asm-offsets.h: asm-offsets.s
diff --git a/xen/Rules.mk b/xen/Rules.mk
index d65d6a48993b..c99c4a9475c9 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -133,6 +133,9 @@ endif
 # Always build obj-bin files as binary even if they come from C source. 
 $(obj-bin-y): XEN_CFLAGS := $(filter-out -flto,$(XEN_CFLAGS))
 
+# To be use with $(a_flags) or $(c_flags) to produce CPP flags
+cpp_flags = $(filter-out -Wa$(comma)% -flto,$(1))
+
 # Calculation of flags, first the generic flags, then the arch specific flags,
 # and last the flags modified for a target or a directory.
 
@@ -222,13 +225,13 @@ $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): %.init.o: %.o FORCE
 	$(call if_changed,obj_init_o)
 
 quiet_cmd_cpp_i_c = CPP     $@
-cmd_cpp_i_c = $(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -MQ $@ -o $@ $<
+cmd_cpp_i_c = $(CPP) $(call cpp_flags,$(c_flags)) -MQ $@ -o $@ $<
 
 quiet_cmd_cc_s_c = CC      $@
 cmd_cc_s_c = $(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -S $< -o $@
 
 quiet_cmd_cpp_s_S = CPP     $@
-cmd_cpp_s_S = $(CPP) $(filter-out -Wa$(comma)%,$(a_flags)) -MQ $@ -o $@ $<
+cmd_cpp_s_S = $(CPP) $(call cpp_flags,$(a_flags)) -MQ $@ -o $@ $<
 
 %.i: %.c FORCE
 	$(call if_changed,cpp_i_c)
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index fe38cfd54421..462472215c91 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -292,7 +292,7 @@ $(BASEDIR)/include/asm-x86/asm-macros.h: asm-macros.i Makefile
 
 efi.lds: AFLAGS-y += -DEFI
 xen.lds efi.lds: xen.lds.S
-	$(CPP) -P $(filter-out -Wa$(comma)%,$(a_flags)) -MQ $@ -o $@ $<
+	$(CPP) -P $(call cpp_flags,$(a_flags)) -MQ $@ -o $@ $<
 
 boot/mkelf32: boot/mkelf32.c
 	$(HOSTCC) $(HOSTCFLAGS) -o $@ $<
diff --git a/xen/arch/x86/mm/Makefile b/xen/arch/x86/mm/Makefile
index b31041644fe8..2818c066f76a 100644
--- a/xen/arch/x86/mm/Makefile
+++ b/xen/arch/x86/mm/Makefile
@@ -15,7 +15,7 @@ guest_walk_%.o: guest_walk.c Makefile
 	$(CC) $(c_flags) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%.i: guest_walk.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CPP) $(call cpp_flags,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%.s: guest_walk.c Makefile
 	$(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@
diff --git a/xen/arch/x86/mm/hap/Makefile b/xen/arch/x86/mm/hap/Makefile
index 22e7ad54bd33..c6d296b51720 100644
--- a/xen/arch/x86/mm/hap/Makefile
+++ b/xen/arch/x86/mm/hap/Makefile
@@ -9,7 +9,7 @@ guest_walk_%level.o: guest_walk.c Makefile
 	$(CC) $(c_flags) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%level.i: guest_walk.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CPP) $(call cpp_flags,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_walk_%level.s: guest_walk.c Makefile
 	$(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@
diff --git a/xen/arch/x86/mm/shadow/Makefile b/xen/arch/x86/mm/shadow/Makefile
index 770213fe9d84..fd64b4dda925 100644
--- a/xen/arch/x86/mm/shadow/Makefile
+++ b/xen/arch/x86/mm/shadow/Makefile
@@ -10,7 +10,7 @@ guest_%.o: multi.c Makefile
 	$(CC) $(c_flags) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_%.i: multi.c Makefile
-	$(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
+	$(CPP) $(call cpp_flags,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -c $< -o $@
 
 guest_%.s: multi.c Makefile
 	$(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -DGUEST_PAGING_LEVELS=$* -S $< -o $@
-- 
Anthony PERARD

On 24.08.2021 12:49, Anthony PERARD wrote:
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
albeit with a remark:

> --- a/xen/Rules.mk
> +++ b/xen/Rules.mk
> @@ -133,6 +133,9 @@ endif
>  # Always build obj-bin files as binary even if they come from C source. 
>  $(obj-bin-y): XEN_CFLAGS := $(filter-out -flto,$(XEN_CFLAGS))
>  
> +# To be use with $(a_flags) or $(c_flags) to produce CPP flags
> +cpp_flags = $(filter-out -Wa$(comma)% -flto,$(1))

Afaics this has nothing to do with Linux'es cpp_flags, so what we do here
is entirely up to us. If this is strictly intended to be used the another
macro, wouldn't it make sense to have

cpp_flags = $(filter-out -Wa$(comma)% -flto,$($(1)))

here and then e.g. ...

> @@ -222,13 +225,13 @@ $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): %.init.o: %.o FORCE
>  	$(call if_changed,obj_init_o)
>  
>  quiet_cmd_cpp_i_c = CPP     $@
> -cmd_cpp_i_c = $(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -MQ $@ -o $@ $<
> +cmd_cpp_i_c = $(CPP) $(call cpp_flags,$(c_flags)) -MQ $@ -o $@ $<

... the slightly simpler / easier to read

cmd_cpp_i_c = $(CPP) $(call cpp_flags,c_flags) -MQ $@ -o $@ $<

here?

Jan