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

[Julien Grall <julien.grall@linaro.org>]

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@linaro.org>
>> ---
>>   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