linux-kernel - Re: [PATCH 1/8] um: Create defconfigs for i386 and x86

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Date:	Thu, 26 Sep 2013 17:27:29 +0530
From:	Ramkumar Ramachandra <artagnon@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	linux-arch@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
	geert@...ux-m68k.org, ralf@...ux-mips.org, lethal@...ux-sh.org,
	Jeff Dike <jdike@...toit.com>,
	Guan Xuetao <gxt@...c.pku.edu.cn>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kbuild@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-m68k@...ts.linux-m68k.org, linux-mips@...ux-mips.org,
	linux-sh@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net,
	Toralf Förster <toralf.foerster@....de>
Subject: Re: [PATCH 1/8] um: Create defconfigs for i386 and x86_64

Richard Weinberger wrote:
>> $ file linux
>> linux: ELF 32-bit LSB  executable, Intel 80386, version 1 (SYSV),
>> dynamically linked (uses shared libs), for GNU/Linux 2.6.32, not
>> stripped
>> $ ./linux ubd0=busybox-rootfs
>> [...]
>> Kernel panic - not syncing: No init found.  Try passing init= option
>> to kernel. See Linux Documentation/init.txt for guidance.
>
> I don't know that rootfs but it looks like there is no init.

Ofcourse there's an init on the busybox-rootfs, and I'm able to boot
it with an x86_64 Linux. The reason for panic is incorrect: I think
(although not sure) a 32-bit rootfs userland will work.

>> [1]    25526 abort (core dumped)  linux ubd0=busybox-rootfs
>>                                                            %
>>
>> Rubbish.
>
> UML core dumps at panic() by design.

On a related note, why does it screw up my terminal? I have to `reset`
to get a nice working terminal.

> Seriously, my plan is to get rid of SUBARCH, that's why I did not push your patches
> upstream and I've send the rid of SUBARCH patch series.
> It turned out that other archs depend on SUBARCH too therefore some more thinking is needed.
> Time passed, merge window closed, $dayjob needed some attention...

Don't let some grand plan stall reasonable patches that fix immediate problems.

> That said, your "arch/um: make it work with defconfig and x86_64" patch is also not perfect.
> "make defconfig ARCH=um SUBARCH=x86" will create x86_64 defconfig, which is wrong and breaks existing
> setups.

Wrong.

  $ make defconfig ARCH=um SUBARCH=i386
  *** Default configuration is based on 'i386_defconfig'
  #
  # configuration written to .config
  #

I can build a 32-bit kernel just fine with my patch applied.
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