linux-kernel - Re: kernel 2.6.39 (user mode linux) crashes (2.6.38 works fine)

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Message-ID: <BANLkTinswk09M7bOup01EnrTNQycNbUMDw@mail.gmail.com>
Date:	Sun, 22 May 2011 01:06:46 +0200
From:	richard -rw- weinberger <richard.weinberger@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Toralf Förster <toralf.foerster@....de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	user-mode-linux-devel@...ts.sourceforge.net,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: kernel 2.6.39 (user mode linux) crashes (2.6.38 works fine)

On Sun, May 22, 2011 at 12:37 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Sat, 2011-05-21 at 12:12 +0200, richard -rw- weinberger wrote:
>> 2011/5/21 Toralf Förster <toralf.foerster@....de>:
>> > Bisecting gave :
>> >
>> >
>> > git bisect badd123375425d7df4b6081a631fc1203fceafa59b2 is the first bad commit
>> > commit d123375425d7df4b6081a631fc1203fceafa59b2
>> > Author: Thomas Gleixner <tglx@...utronix.de>
>> > Date:   Wed Jan 26 21:32:01 2011 +0100
>> >
>> >    rwsem: Remove redundant asmregparm annotation
>> >
>> >    Peter Zijlstra pointed out, that the only user of asmregparm (x86) is
>> >    compiling the kernel already with -mregparm=3. So the annotation of
>> >    the rwsem functions is redundant. Remove it.
>>
>> Ok, this bisect makes much more sense.
>>
>> Thomas, Peter, please revert d123375425d7df4b6081a631fc1203fceafa59b2.
>> We cannot compile UML with -mregparm=3 it would cause a lot of trouble.
>> It would break 32bit UML on 64bit and also on older 32bit systems like RHEL5.
>
> But why?

Why reverting?
d123375 effectively reverts commit d50efc6c (x86: fix UML and -regparm=3).

> Also, having to carry that asmregparm notation just for uml doesn't seem
> worth the trouble.
>

Frankly, I don't know why exactly UML breaks without having asmregparm.
I've seen this -regparm=3 thing today the very first time, I'll dig into it...

-- 
Thanks,
//richard
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