Re: [Xen-devel] [PATCH 7/8] xen/arm: Set foreign page type to p2m_map_foreign

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 12/05/2013 04:34 PM, Ian Campbell wrote:
> On Thu, 2013-12-05 at 15:42 +0000, Julien Grall wrote:
> > Xen needs to know that the current page belongs to another domain. Also take
> > the refcount to this page.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> > ---
> >   xen/arch/arm/mm.c |   14 +++++++++-----
> >   1 file changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> > index 960c872..bf383a7 100644
> > --- a/xen/arch/arm/mm.c
> > +++ b/xen/arch/arm/mm.c
> > @@ -977,6 +977,7 @@ static int xenmem_add_to_physmap_one(
> >   {
> >       unsigned long mfn = 0;
> >       int rc;
> > +    p2m_type_t t = p2m_ram_rw;
> Can we set this explicitly on a per-mapspace basis please, so the
> compiler will complain about an uninitialised variable if we forget to
> add the type for a new map space, instead of silently creating writable
> ram mappings.
Actually, GCC compiler won't complain if t is not set in one of the case.
If have tried this following dummy function on several version of GCC 
(the most recent is 4.8.2) and they don't emit any warning.
=================================================================
int f (int a)
{
    int b;

    switch (a)
    {
    case 1:
        b = 1;
        break;
    case 2:
        /* b is unset */
        break;
    }

    return b;
}
====================================================================

I have also tried clang, and I effectively get an error. But we don't 
yet support clang for Xen ARM port.
I have found a bug report opened in 2004 for this kind of bug, but never 
fixed... (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18501).
--
Julien Grall

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