Re: [Xen-devel] [PATCH] xen: Avoid left shifting into a sign bit

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Thursday, February 18, 2016 3:52 AM
> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Jan Beulich
> <JBeulich@xxxxxxxx>; Tim Deegan <tim@xxxxxxx>; Ian Campbell
> <Ian.Campbell@xxxxxxxxxx>; Tian, Kevin <kevin.tian@xxxxxxxxx>; Wu, Feng
> <feng.wu@xxxxxxxxx>
> Subject: [PATCH] xen: Avoid left shifting into a sign bit
> 
> Clang 3.8 notices, and objects because it is undefined behaviour.
> 
> "error: shifting a negative signed value is undefined 
> [-Werror,-Wshift-negative-
> value]"
> 
> Use unsigned constants rather than signed ones.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Tim Deegan <tim@xxxxxxx>
> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> CC: Feng Wu <feng.wu@xxxxxxxxx>
> ---
>  xen/common/page_alloc.c               | 2 +-
>  xen/drivers/passthrough/vtd/x86/ats.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)

Acked-by: Feng Wu <feng.wu@xxxxxxxxx>  for the VT-d part.

Thanks,
Feng

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