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Date:   Mon, 28 Mar 2022 08:41:53 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [PATCH] x86/config: Make the x86 defconfigs a bit more usable
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On Sun, Mar 27, 2022 at 09:03:14PM +0200, Ingo Molnar wrote:
> Yeah, good catch! ...
> 
> I use defconfigs by explicitly adding in the architecture:
> 
>   kepler:~/tip> make ARCH=i386 defconfig
> 
>   kepler:~/tip> kconfig-arch
>   i386
> 
> ... so never I noticed this bug.

Ah, good point!

> I fixed this in the latest version (attached).
> 
> Arguably 'make ARCH=i386 savedefconfig' should preserve this, so that 
> refreshing defconfigs on bi-arch architectures is idempotent, but that's no 
> excuse to regress the existing defconfig behavior.

Hmmm, I thought that it would, but I think the behavior of savedefconfig
is actually correct with regards to how it handles CONFIG_64BIT in the
presence of an explicit ARCH value, based on how CONFIG_64BIT is
defined:

config 64BIT
	bool "64-bit kernel" if "$(ARCH)" = "x86"
	default "$(ARCH)" != "i386"
	help
	  Say yes to build a 64-bit kernel - formerly known as x86_64
	  Say no to build a 32-bit kernel - formerly known as i386

As the default is no when ARCH == i386 and there is no prompt in that
situation, "# CONFIG_64BIT is not set" gets dropped, as that is the
default. Using savedefconfig without the ARCH variable would do the
right thing.

I tried playing around with these Kconfig symbols to see if I could get
something that would work for savedefconfig with or without ARCH, but I
could not really come up with anything. I did not try super hard though,
it might still be possible.

Cheers,
Nathan