Re: [PATCH] build: generic top-level rule to build individual files

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.03.2022 12:28, Anthony PERARD wrote:
> On Mon, Mar 28, 2022 at 09:41:26AM +0200, Jan Beulich wrote:
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -75,6 +75,13 @@ ifeq (x86_64,$(XEN_TARGET_ARCH))
>>      XEN_TARGET_ARCH=x86_32 $(MAKE) -C stubdom pv-grub-if-enabled
>>  endif
>>  
>> +define do-subtree
>> +$(1)/%: FORCE
>> +    $$(MAKE) -C $(1) $$*
>> +endef
>> +
>> +$(foreach m,$(wildcard */Makefile),$(eval $(call do-subtree,$(patsubst 
>> %/Makefile,%,$(m)))))
> 
> Any reason to not use $(SUBSYSTEMS) instead of $(wildcard ) ? Or maybe
> you would rather been able to run `make xen/foo/bar.o` even after
> running `./configure --disable-xen`.

This particular case I don't care about as much, but I think it is
helpful if any subtree which has a Makefile can be recursed into
this way. That way if someone hooks other trees (xtf, mini-os) into
the tree, they're as accessible. As would be subtrees which aren't
subsystems by which still have a Makefile (such may or may not
appear).

>> @@ -334,3 +341,6 @@ uninstall: uninstall-tools-public-header
>>  .PHONY: xenversion
>>  xenversion:
>>      @$(MAKE) --no-print-directory -C xen xenversion
>> +
>> +PHONY += FORCE
> 
> That's a Kbuild construct which will not work here. You need to write
> ".PHONY: FORCE" instead.
> 
> In Kbuild, there's a ".PHONY: $(PHONY)", and various macros needs to
> know what's .PHONY.

Oh, right - thanks for pointing out. I should have really noticed by
looking at context in the file ...

> With at least the .PHONY business taking care of: Reviewed-by: Anthony PERARD 
> <anthony.perard@xxxxxxxxxx>

Thanks.

Jan