Re: [Xen-devel] [PATCH 2/4] xen/arm: initialize access

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 15 Oct 2018, Tamas K Lengyel wrote:
> On Mon, Oct 15, 2018 at 3:57 AM Stefano Stabellini
> <sstabellini@xxxxxxxxxx> wrote:
> >
> > Initialize variable *access before returning it back to the caller.
> >
> > Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> > ---
> >  xen/arch/arm/mem_access.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/xen/arch/arm/mem_access.c b/xen/arch/arm/mem_access.c
> > index ba4ec78..10ab308 100644
> > --- a/xen/arch/arm/mem_access.c
> > +++ b/xen/arch/arm/mem_access.c
> > @@ -47,6 +47,7 @@ static int __p2m_get_mem_access(struct domain *d, gfn_t 
> > gfn,
> >      };
> >
> >      ASSERT(p2m_is_locked(p2m));
> > +    *access = XENMEM_access_n;
> 
>  Why XENMEM_access_n and why set this at all here?

Hi Tamas,

Yes, I missed an explanation. Initializing variables before passing them
as parameter or as a return value to a function is a safety
certification requirement. Also, it makes the code a bit nicer.

In the specific case of this function, *access is initialized before
returning in all cases but the return -ESRCH case. I thought the nicer
way to make sure *access is always initialized, making the code more
robust, would be to initialize *access at the beginning of the function
with a restrictive value.

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