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Date:   Sat, 29 Jul 2023 09:45:18 +0200
From:   Willy Tarreau <w@1wt.eu>
To:     Zhangjin Wu <falcon@tinylab.org>
Cc:     arnd@arndb.de, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux@weissschuh.net,
        thomas@t-8ch.de
Subject: Re: [PATCH v1 4/8] selftests/nolibc: add extra config file customize
 support
Message-ID: <20230729074518.GH956@1wt.eu>
References: <20230722120037.GA17311@1wt.eu>
 <20230725143006.37452-1-falcon@tinylab.org>
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Hi Zhangjin,

On Tue, Jul 25, 2023 at 10:30:06PM +0800, Zhangjin Wu wrote:
> Hi, Willy
> 
> > On Wed, Jul 19, 2023 at 05:14:07AM +0800, Zhangjin Wu wrote:
> > > The default DEFCONFIG_<ARCH> may not always work for all architectures,
> > > some architectures require to add extra kernel config options, this adds
> > > a new 'extconfig' target for this requirement.
> > > 
> > > It allows to customize extra kernel config options via the common
> > > common.config and the architecture specific <ARCH>.config, at last
> > > trigger 'allnoconfig' to let them take effect with missing config
> > > options as disabled.
> > > 
> > > The scripts/kconfig/merge_config.sh tool is used to merge the extra
> > > config files.
> > > 
> > > Suggested-by: Thomas Wei?schuh <linux@weissschuh.net>
> > > Link: https://lore.kernel.org/lkml/67eb70d4-c9ff-4afc-bac7-7f36cc2c81bc@t-8ch.de/
> > > Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
> > > ---
> > >  tools/testing/selftests/nolibc/Makefile | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/tools/testing/selftests/nolibc/Makefile b/tools/testing/selftests/nolibc/Makefile
> > > index f42adef87e12..08a5ca5f418b 100644
> > > --- a/tools/testing/selftests/nolibc/Makefile
> > > +++ b/tools/testing/selftests/nolibc/Makefile
> > > @@ -39,6 +39,9 @@ DEFCONFIG_s390       = defconfig
> > >  DEFCONFIG_loongarch  = defconfig
> > >  DEFCONFIG            = $(DEFCONFIG_$(ARCH))
> > >  
> > > +# extra kernel config files under configs/, include common + architecture specific
> > > +EXTCONFIG            = common.config $(ARCH).config
> > > +
> > >  # optional tests to run (default = all)
> > >  TEST =
> > >  
> > > @@ -162,6 +165,10 @@ initramfs: nolibc-test
> > >  defconfig:
> > >  	$(Q)$(MAKE) -C $(srctree) ARCH=$(ARCH) CC=$(CC) CROSS_COMPILE=$(CROSS_COMPILE) mrproper $(DEFCONFIG) prepare
> > >  
> > > +extconfig:
> > > +	$(Q)$(srctree)/scripts/kconfig/merge_config.sh -O "$(srctree)" -m "$(srctree)/.config" $(foreach c,$(EXTCONFIG),$(wildcard $(CURDIR)/configs/$c))
> > > +	$(Q)$(MAKE) -C $(srctree) ARCH=$(ARCH) CC=$(CC) CROSS_COMPILE=$(CROSS_COMPILE) KCONFIG_ALLCONFIG="$(srctree)/.config" allnoconfig
> > > +
> > 
> > Please also mention this entry in the "help" message.
> > Other than that, OK.
> >
> 
> Willy, as we discussed in another tinyconfig series, in order to avoid
> add more complexity to users, I plan to drop this standalone 'extconfig'
> target and move the extra config operations to defconfig target like
> this:
> 
>     defconfig:
>      	$(Q)$(MAKE) -C $(srctree) ARCH=$(ARCH) CC=$(CC) CROSS_COMPILE=$(CROSS_COMPILE) mrproper $(DEFCONFIG) prepare
>      	$(Q)$(srctree)/scripts/kconfig/merge_config.sh -O "$(srctree)" -m "$(srctree)/.config" $(foreach c,$(EXTCONFIG),$(wildcard $(CURDIR)/configs/$c))
>      	$(Q)$(MAKE) -C $(srctree) ARCH=$(ARCH) CC=$(CC) CROSS_COMPILE=$(CROSS_COMPILE) KCONFIG_ALLCONFIG="$(srctree)/.config" allnoconfig
> 
> This extra config options are really critical to default boot and test, so, it
> should be a 'default' config action as the 'defconfig' target originally mean.
> 
> Will test carefully about this change, what's your idea?

Well, *iff* we need to have per-arch config settings, probably to better
support Qemu, the console output, etc, then indeed we'd rather add them
to all configs indeed. However the example above is bogus. First you
create a default config, then prepare the rest of the kernel, then
merge that config with the extensions (based on the arch and not the
sub-arch BTW) then erase everything to restart from an allnoconfig.

Also if you're using merge_config you'll need -Q to disable warning
about overridden options since you're starting from a defconfig which
contains plenty of them. Usually I just do defconfig, append the few
changes, then oldconfig and that's done. But merge_config can probably
be fine as well. Also make prepare should be done last, to make sure
that if it depends on anything in the config (e.g. 32 vs 64 bit etc)
it's up to date.

Willy