Hi.
Is there a good way to set a specific variable 'BUILDING_FOO'
while Make is building the target 'foo' including its prerequisites?
Let's say we have two targets 'vmlinux' and 'modules', but
the actual build rules are factored out into '__common'.
[Not-working code]
------------------>8-------------------------
.PHONY: vmlinux modules __common
vmlinux: export BUILDING_VMLINUX=y
modules: export BUILDING_MODULES=y
vmlinux modules: __common
@:
__common:
@echo BUILDING_VMLINUX is $(BUILDING_VMLINUX)
@echo BUILDING_MODULES is $(BUILDING_MODULES)
[ common build rules, which internally uses
BUILDING_{VMLINUX,MODULES} conditionals ]
------------------>8-------------------------
My hope is:
- 'make vmlinux' builds __common with BUILDING_VMLINUX=y
- 'make modules' builds __common with BUILDING_MODULES=y
- 'make vmlinux modules' builds __common with
BUILDING_VMLINUX=y and BUILDING_MODULES=y
I know the example above does not work like that.
[Working code]
------------------>8-------------------------
.PHONY: vmlinux modules __common
ifneq ($(filter vmlinux,$(MAKECMDGOALS)),)
export BUILDING_VMLINUX=y
endif
ifneq ($(filter modules,$(MAKECMDGOALS)),)
export BUILDING_MODULES=y
endif
vmlinux modules: __common
@:
__common:
@echo BUILDING_VMLINUX is $(BUILDING_VMLINUX)
@echo BUILDING_MODULES is $(BUILDING_MODULES)
[ common build rules, which internally uses
BUILDING_{VMLINUX,MODULES} conditionals ]
------------------>8-------------------------
'make foo bar' builds __common, setting
BUILDING_VMLINUX and BUILDING_MODULES,
but we need to add more filtering code to handle
'make', 'make all', and other targets that
depend on 'vmlinux' and 'modules'.
The Linux kernel build system actually does this:
https://github.com/torvalds/linux/blob/v5.12/Makefile#L633
https://github.com/torvalds/linux/blob/v5.12/Makefile#L637
but, the filtering pattern tends to grow uglily if we try to
cover all the possible targets.
Is there any way to do this better?
--
Best Regards
Masahiro Yamada
