Re: [XEN PATCH v4 10/18] xen/build: use if_changed on built_in.o

[Jan Beulich <jbeulich@xxxxxxxx>]

On 31.03.2020 12:30, Anthony PERARD wrote:
> --- a/xen/Rules.mk
> +++ b/xen/Rules.mk
> @@ -130,15 +130,24 @@ include $(BASEDIR)/arch/$(TARGET_ARCH)/Rules.mk
>  c_flags += $(CFLAGS-y)
>  a_flags += $(CFLAGS-y) $(AFLAGS-y)
>  
> -built_in.o: $(obj-y) $(extra-y)
> -ifeq ($(obj-y),)
> -     $(CC) $(c_flags) -c -x c /dev/null -o $@
> -else
> +quiet_cmd_ld_builtin = LD      $@
>  ifeq ($(CONFIG_LTO),y)
> -     $(LD_LTO) -r -o $@ $(filter-out $(extra-y),$^)
> +cmd_ld_builtin = \
> +    $(LD_LTO) -r -o $@ $(filter-out $(extra-y),$(real-prereqs))
>  else
> -     $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out $(extra-y),$^)
> +cmd_ld_builtin = \
> +    $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out $(extra-y),$(real-prereqs))
>  endif

How about going yet one step further and doing away with the
ifeq here altogether:

cmd_ld_builtin-y = \
    $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out $(extra-y),$(real-prereqs))
cmd_ld_builtin-$(CONFIG_LTO) = \
    $(LD_LTO) -r -o $@ $(filter-out $(extra-y),$(real-prereqs))

> +quiet_cmd_cc_builtin = LD      $@
> +cmd_cc_builtin = \
> +    $(CC) $(XEN_CFLAGS) -c -x c /dev/null -o $@
> +
> +built_in.o: $(obj-y) $(extra-y) FORCE
> +ifeq ($(obj-y),)
> +     $(call if_changed,cc_builtin)
> +else
> +     $(call if_changed,ld_builtin)

        $(call if_changed,ld_builtin-y)

?

As an aside (not something you introduce) this makes it even more
prominent that the use of $(XEN_LDFLAGS) is asymmetric here, for
whatever reason (if any). Of course there's other redundancy
between the two commands which could be eliminated.

Jan