Re: [PATCH] build: centralize / unify asm-offsets generation

From: Jan Beulich <jbeulich@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Ian Jackson <iwj@xenproject.org>, Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH] build: centralize / unify asm-offsets generation
Date: Wed, 21 Apr 2021 16:09:03 +0200	[thread overview]
Message-ID: <5170aa51-8e34-3a45-5bf6-c0a187b1c427@suse.com> (raw)
In-Reply-To: <YH7/SvkrB2yGgRij@Air-de-Roger>

On 20.04.2021 18:20, Roger Pau Monné wrote:
> On Tue, Apr 20, 2021 at 05:47:49PM +0200, Jan Beulich wrote:
>> On 20.04.2021 17:29, Roger Pau Monné wrote:
>>> On Thu, Apr 01, 2021 at 10:33:47AM +0200, Jan Beulich wrote:
>>>> @@ -399,7 +399,11 @@ include/xen/compile.h: include/xen/compi
>>>>  	@sed -rf tools/process-banner.sed < .banner >> $@.new
>>>>  	@mv -f $@.new $@
>>>>  
>>>> -include/asm-$(TARGET_ARCH)/asm-offsets.h: arch/$(TARGET_ARCH)/asm-offsets.s
>>>> +asm-offsets.s: arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.c
>>>> +	$(CC) $(filter-out -Wa$(comma)% -flto,$(c_flags)) -S -g0 -o $@.new -MQ $@ $<
>>>> +	$(call move-if-changed,$@.new,$@)
>>>
>>> Won't it be more natural to keep the .s file in arch/$(TARGET_ARCH)?
>>
>> Yes and no: Yes as far as the actual file location is concerned.
>> No when considering where it gets generated: I generally consider
>> it risky to generate files outside of the directory where make
>> currently runs. There may be good reasons for certain exceptions,
>> but personally I don't see this case as good enough a reason.
>>
>> Somewhat related - if doing as you suggest, which Makefile's
>> clean: rule should clean up that file in your opinion?
> 
> The clean rule should be in the makefile where it's generated IMO,
> same as asm-offsets.h clean rule currently in xen/Makefile.
> 
>> Nevertheless, if there's general agreement that keeping the file
>> there is better, I'd make the change and simply ignore my unhappy
>> feelings about it.
> 
> I don't have a strong opinion, it just feels weird to have this IMO
> stray asm-offsets.s outside of it's arch directory, taking into
> account that we have asm-offsets.h generated from xen/Makefile into an
> arch specific directory already as a precedent in that makefile.

Well, asm-offsets.h generation doesn't involve the compiler, hence
no .*.d files get generated and want including later. For
asm-offsets.s to have dependencies properly honored, if we
generated it in xen/arch/<arch>, .asm-offsets.d would also end up
there, and hence including of it would need separately taking care
of.

Jan