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Re: [PATCH] x86emul: replace UB shifts

To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Date: Fri, 31 Jul 2020 11:50:06 +0100
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Cc: Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 31/07/2020 08:06, Jan Beulich wrote:
> Displacement values can be negative, hence we shouldn't left-shift them.
>
> While auditing shifts, I noticed a pair of missing parentheses, which
> also get added right here.
>
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I'd suggest putting the UBSAN report into the commit message

(XEN) UBSAN: Undefined behaviour in x86_emulate/x86_emulate.c:3482:55
(XEN) left shift of negative value -2

Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

References:
- [PATCH] x86emul: replace UB shifts
  - From: Jan Beulich

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