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xen-ppc-devel
[Xen-devel] Re: [rfc] [patch] grant_entry.flags accessors
On 27 Jun 2006, at 16:06, Hollis Blanchard wrote:
In the couple cases so far, we know that even though the field is only
one or two bytes, it's actually safe to do a four-byte load/store to it
because the containing structure is large enough.
I'm not really comfortable with making that a blanket assumption. I'd
really like to know exactly what we're overwriting when performing
these
hacks^Woperations.
You won't be overwriting anything else since you'll be performing an
atomic read-modify-write that does not change any of the bits outside
the subword of interest. More precisely, you may overwrite those bits
outside the subword, but it's guaranteed to be with the current
contents so there'll be no externally visible change and you won't
clobber anything. Since you'll do an aligned longword operation you
can't end up straddling a page boundary or anything nasty like that.
-- Keir
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