Re: [Xen-devel] [XEN PATCH v3 15/23] xen/build: have the root Makefile generates the CFLAGS

From: Jan Beulich <jbeulich@suse.com>
To: Anthony PERARD <anthony.perard@citrix.com>
Cc: "Stefano Stabellini" <sstabellini@kernel.org>,
	"Julien Grall" <julien@xen.org>, "Wei Liu" <wl@xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xenproject.org,
	"Daniel De Graaf" <dgdegra@tycho.nsa.gov>,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [XEN PATCH v3 15/23] xen/build: have the root Makefile generates the CFLAGS
Date: Wed, 18 Mar 2020 11:20:44 +0100	[thread overview]
Message-ID: <fffc904e-bbc2-f19c-7a76-cdbaf56a0cba@suse.com> (raw)
In-Reply-To: <20200317183503.GB4088@perard.uk.xensource.com>

On 17.03.2020 19:35, Anthony PERARD wrote:
> On Wed, Mar 04, 2020 at 04:00:52PM +0100, Jan Beulich wrote:
>> On 26.02.2020 12:33, Anthony PERARD wrote:
>>> @@ -113,6 +115,64 @@ $(KCONFIG_CONFIG):
>>> +AFLAGS += -D__ASSEMBLY__
>>> +
>>> +CFLAGS += $(CFLAGS-y)
>>
>> I can't seem to be able to spot a similar line for AFLAGS.
> 
> I didn't add any because it wasn't necessary.

Symmetry / consistency would still be desirable imo.

>>> @@ -107,7 +65,7 @@ $(foreach o,$(filter-out %/,$(obj-y) $(obj-bin-y) $(extra-y)),$(eval $(call gend
>>>   subdir-y := $(subdir-y) $(filter %/, $(obj-y))
>>>   obj-y    := $(patsubst %/, %/built_in.o, $(obj-y))
>>>   
>>> -$(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS += -DINIT_SECTIONS_ONLY
>>> +$(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS-y += -DINIT_SECTIONS_ONLY
>>
>> While in the description you say "We can't use CFLAGS in
>> subdirectories to add flags to particular targets, ...", it
>> remains unclear there why that is, and hence why changes like
>> this one are necessary. If this is a restriction that's going to
>> remain, this also needs writing down in a prominent place. After
> 
> Yes, I should probably start writing some documentation, probably
> following the kind of documentation that Linux has for kbuild, and I
> could put that in docs/misc, along side the kconfig doc. That probably
> not a prominent place, but I don't know if there's a better place.

If it's to live under docs/, then I guess xen/Rules.mk should at
least point to that documentation (perhaps in a comment near the
first setting or consumption of CFLAGS-y).

Jan

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