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Re: [Xen-devel] [PATCH 2/2 v2] xen: arm: Set all bits in mfn_to_xen_entry()

On 21/08/2015 12:47, Chris (Christopher) Brand wrote:
Hi Andrew,

On 21/08/15 00:33, Chris Brand wrote:
Ensure that every bit has a specific value.

Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
Signed-off-by: Chris Brand <chris.brand@xxxxxxxxxxxx>
v2 adds comments on pxn and avail.

This is no functional change, if the compiler is conforming to the C spec.

The spec guarantees that structure initialisation like this causes unspecified
names to gain their default value.  As these are integer bitfields, the default
value is 0.

What compiler is in use?  It would appear that it is buggy, or at least has
buggy scalar replacement optimisations.

That's right. I'd forgotten about that. This was actually suggested by Julien in
a review of another patch I sent. I haven't seen any problems this fixes.

I still think those patches are valid in order to know which value are set by default and what does it mean.


Julien Grall

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