linux-kernel - Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

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Date:	Tue, 13 Jul 2010 19:34:17 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Palfrader <peter@...frader.org>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Glauber Costa <glommer@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [patch 134/149] x86, paravirt: Add a global synchronization	point
 for pvclock

On 07/13/2010 07:22 PM, Peter Palfrader wrote:
>>>
>>> weasel@...repid:~$ publish System.map
>>> http://asteria.noreply.org/~weasel/volatile/2010-07-13-mbm2xEdd8Q4/System.map
>>> weasel@...repid:~$ grep -i last_value System.map
>>> ffffffff81712e80 r last_value
>>> ffffffff81b05240 b last_value.26163
>>>
>>>        
>> "r" = "read only"
>>
>> How does it look in 'nm arch/x86/kernel/pvclock.o'?
>>      
> The same:
>
> [git|v2.6.32.16] weasel@...lma:/scratch/kernel/2.6.32.16$ nm arch/x86/kernel/pvclock.o
> 0000000000000000 r last_value
>                   U native_read_tsc
> 0000000000000040 T pvclock_clocksource_read
> 0000000000000100 T pvclock_read_wallclock
> 0000000000000000 T pvclock_tsc_khz
>                   U set_normalized_timespec
>    

But it's

>
> static atomic64_t last_value = ATOMIC64_INIT(0);
>

Doesn't make any sense.

Let's try to see if the toolchain is confused:

- rename last_value to some random name
- drop the 'static' qualifier
- drop the '= ATOMIC64_INIT(0)'
- all of the above

(better start with the last).

No need to rebuild everything, just look at the output of nm pvclock.o.

My bet is that dropping 'static' will fix it.  We may have the wrong 
constraints on atomic64_cmpxchg64(), so the compiler thinks we never 
change last_value.

-- 
error compiling committee.c: too many arguments to function

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