From mboxrd@z Thu Jan  1 00:00:00 1970
From: Corneliu ZUZU <czuzu@bitdefender.com>
Subject: Re: [PATCH v3 2/2] xen/vm-events: Move parts of
 monitor_domctl code to common-side.
Date: Mon, 15 Feb 2016 18:28:43 +0200
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To: Jan Beulich <JBeulich@suse.com>
Cc: Tamas K Lengyel <tamas@tklengyel.com>, Keir Fraser <keir@xen.org>, Ian Campbell <ian.campbell@citrix.com>, Razvan Cojocaru <rcojocaru@bitdefender.com>, Andrew Cooper <andrew.cooper3@citrix.com>, xen-devel@lists.xen.org, Stefano Stabellini <stefano.stabellini@citrix.com>
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On 2/15/2016 4:08 PM, Jan Beulich wrote:
>
>> After changing 1 to 1U though, I don't understand why we should also
>> range-check mop->event.
>> I'm imagining when (mop->event > 31):
>> * (1U << mop->event) = 0 or >= (0x1 + 0xFFFFFFFF) (?)
> No, it's plain undefined.

Weirdo C, didn't know that!
I've just read http://www.danielvik.com/2010/05/c-language-quirks.html .
That's crazy, I can't believe such 'quirks' exist and that I never knew 
of them.
So then, would this do:

/* sanity check - avoid '<<' operator undefined behavior */
if ( unlikely(mop->event > 31) )
     return -EINVAL;
if ( unlikely(!(arch_monitor_get_capabilities(d) & (1U << mop->event))) )
     return -EOPNOTSUPP;


?

Thanks,
Corneliu.