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

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Apr 27, 2021 at 02:30:35PM +0200, Jan Beulich wrote:
> On 27.04.2021 11:05, Roger Pau Monné wrote:
> > On Wed, Apr 21, 2021 at 04:09:03PM +0200, Jan Beulich wrote:
> >> 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.
> > 
> > I'm not sure I understand what do you mean with inclusion need taking
> > care of separately. Isn't it expected for .d file to reside in the
> > same directory as the output,
> 
> Yes, ...
> 
> > and hence picked up automatically?
> 
> ... and hence they _wouldn't_ be picked up automatically while
> building in xen/ if the .s file got created in xen/arch/<arch>/.

Hm, so that would prevent re-building the target when the dependencies
changed as the .d file being in the arch directory would attempt the
rebuild from there instead of the top level xen/?

I guess the alternative would be to force a rebuild of the target
every time, in order to not depend on the .d logic?

Thanks, Roger.