Re: [Xen-devel] [PATCH v5 03/10] x86: determine HAVE_AS_* just once

[Jan Beulich <jbeulich@suse.com>]

On 25.03.2020 22:12, Andrew Cooper wrote:
> On 24/03/2020 12:33, Jan Beulich wrote:
>> With the exception of HAVE_AS_QUOTED_SYM, populate the results into a
>> generated header instead of (at least once per [sub]directory) into
>> CFLAGS. This results in proper rebuilds (via make dependencies) in case
>> the compiler used changes between builds. It additionally eases
>> inspection of which assembler features were actually found usable.
>>
>> Some trickery is needed to avoid header generation itself to try to
>> include the to-be/not-yet-generated header.
>>
>> Since the definitions in generated/config.h, previously having been
>> command line options, might even affect xen/config.h or its descendants,
>> move adding of the -include option for the latter after inclusion of the
>> per-arch Rules.mk. Use the occasion to also move the most general -I
>> option to the common Rules.mk.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Given the work of Anthony's which is already committed in staging, I'd
> really prefer this patch to look something like
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=WIP.x86/asm&id=95ef9f80ed6359e89f988121521c421b7e9528de
> 
> That avoids all fragile games with includes, and is the position we want
> to be in, longterm.

Ah, so they already have something going in that direction. Looks
okay to me, albeit ...

> All the requisite infrastructure looks to be already present.

... there's the one open prereq question of what happens upon
tool chain updates. It's not clear to me if/how kconfig would
get invoked despite none of the recorded dependencies having
changed in such a case. (I'm sure you realize there's no issue
with this when the determination occurs out of a makefile.)

Jan