linux-kernel - Re: [uml-devel] [PATCH] checkstack: use $UTS

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Date:	Tue, 08 Jul 2014 10:50:58 +0200
From:	Richard Weinberger <richard@....at>
To:	Konstantin Khlebnikov <koct9i@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	UML devel <user-mode-linux-devel@...ts.sourceforge.net>,
	linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: [uml-devel] [PATCH] checkstack: use $UTS_MACHINE as target architecture

Am 08.07.2014 10:47, schrieb Konstantin Khlebnikov:
> On Tue, Jul 8, 2014 at 12:33 PM, Richard Weinberger <richard@....at> wrote:
>> Am 08.07.2014 10:30, schrieb Konstantin Khlebnikov:
>>> On Tue, Jul 8, 2014 at 12:20 PM, Richard Weinberger <richard@....at> wrote:
>>>> Am 08.07.2014 10:16, schrieb Konstantin Khlebnikov:
>>>>> On Tue, Jul 8, 2014 at 12:01 PM, Richard Weinberger
>>>>> <richard.weinberger@...il.com> wrote:
>>>>>> On Tue, Jul 8, 2014 at 7:48 AM, Konstantin Khlebnikov <koct9i@...il.com> wrote:
>>>>>>> On Tue, Jul 8, 2014 at 2:05 AM, Andrew Morton <akpm@...ux-foundation.org> wrote:
>>>>>>>> On Sat, 05 Jul 2014 15:22:38 +0400 Konstantin Khlebnikov <koct9i@...il.com> wrote:
>>>>>>>>
>>>>>>>>> This fixes command # make checkstack for i386/x86_64.
>>>>>>>>> Looks like $UTS_MACHINE is exactly what scripts/checkstack.pl needs.
>>>>>>>>>
>>>>>>>>> By default $UTS_MACHINE is equal to $ARCH, but some arch/${ARCH}/Makefile
>>>>>>>>> overrides it. This patch updates it also in arch/x86/Makefile.um
>>>>>>>>>
>>>>>>>>> broken in ffee0de ("x86: Default to ARCH=x86 to avoid overriding CONFIG_64BIT")
>>>>>>>>
>>>>>>>> The changelog doesn't describe the bug which is being fixed.  It should
>>>>>>>> do so please.  If there are any compiler/make error messages then those
>>>>>>>> should be included.
>>>>>>>>
>>>>>>>
>>>>>>> Oh, ok. checkstalk.pl needs either i386 or x86_64, x86 isn't enough.
>>>>>>>
>>>>>>> $ make checkstack
>>>>>>> objdump -d vmlinux $(find . -name '*.ko') | \
>>>>>>> perl /home/blind/src/linux-stable/scripts/checkstack.pl x86
>>>>>>> wrong or unknown architecture "x86"
>>>>>>
>>>>>> And now we need ARCH, SUBARCH and UTS_MACHINE on UML? :-(
>>>>>
>>>>> Nope UTS_MACHINE is autodetected, see hunk Makefile.x86 in my patch.
>>>>>
>>>>> I thought about cleaning this part of UML.
>>>>> For example we could move arch/x86/um into arch/um/x86 and use # make
>>>>> ARCH=um/x86
>>>>
>>>> No way. We moved the x86 stuff to arch/x86/ a few Years ago by design.
>>>
>>> Ok, fine. We could leave it in arch/x86/um and use make ARCH=x86/um
>>
>> I don't like this. Please keep ARCH=um as is.
>>
>>>>
>>>>> after collecting this stuff together it woud be easier to get rid of
>>>>> forever-broken parts.
>>>>> As I see UML has been designed to work everywhere but SMP seem never worked
>>>>> as well as any host os except of linux or other arch except x86.
>>>>
>>>> Currently UML runs only on x86_32/64.
>>>> Adding/fixing SMP support should be doable.
>>>
>>> This might be quite difficult on top of current ptrace-based design.
>>> I thought about running userspace in kvm context, this might be much
>>> faster than ptrace but requires indirect uaccess like for 4gb-split.
>>> But it's very unlikely that I'll find time for that.
>>
>> Erm, UML is a systemcall emulator based on ptrace().
>> If you make it use any KVM backend there is 0 usecase for UML because we can just use qemu/kvmtool.
> 
> But kernel stays in userspace, so it could be easily debugged.
> It's like merge kvmtool+linux into one application.

You can already do this with qemu. It has a -gdb switch.

Thanks,
//richard
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