linux-kernel - Re: building in 32bit chroot on x86

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Message-ID: <CA+55aFwiyuA4fKztofM-fdDSc+ZH9aAR1xksL8ZWRDE-pdXruw@mail.gmail.com>
Date:   Tue, 5 Jun 2018 12:13:54 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     tmb@...eia.org, Ulf Magnusson <ulfalizer@...il.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: building in 32bit chroot on x86_64 host broken

On Tue, Jun 5, 2018 at 11:50 AM Thomas Backlund <tmb@...eia.org> wrote:
> >
> > but why do you care?
>
> Because without it running the build in the 32bit chroot will get the
> initial reported issue:

Ahh. I can re-create that now.

Yes, doing

      make ARCH=i386 allnoconfig

followed by

      make oldconfig

is broken. And doing a trivial "git bisect run" to pinpoint where
CONFIG_64BIT goes away gives us

f467c5640c29ad258c3cd8186a776c82fc3b8057 is the first bad commit

which does that

  "kconfig: only write '# CONFIG_FOO is not set' for visible symbols"

and it turns out that CONFIG_64BIT is not a visible symbol on x86-32,
because that question is disabled when ARCH != "x86".

        bool "64-bit kernel" if ARCH = "x86"

And the problem with that, is that *next* time around this config file
is used, because we don't have that

  # CONFIG_64BIT is not set

line, we don't turn it into

  CONFIG_64BIT=n

and then the "depends on" in X86_64

  config X86_64
          def_bool y
          depends on 64BIT

no longer hides it.

Hmm. Ulf, Masahiro, comments?

Should we just revert that commit?

Thomas, can you verify that a

        git revert f467c5640c29ad258c3cd8186a776c82fc3b8057

fixes the problem for you?

              Linus