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

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Date:	Tue, 08 Jul 2014 10:33:56 +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 10:30, 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.

Thanks,
//richard
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