On 08/04/2020 13:40, Jan Beulich wrote: > 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))
Please don't. Logic like this is substantially harder to follow than a plain if/else construct, and clarity is of far higher importance than optimising the line count in the build system. This trick only works for trivial cases, and interferes with diff's when the logic inevitably becomes less trivial. LTO support in particular needs a complete overhaul, but there is no way I'm going to touch that with a barge pole until this series is in place. ~Andrew
