Re: [Xen-devel] [PATCH] drm/xen-front: fix pointer casts

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

On 05/23/2018 02:06 PM, Juergen Gross wrote:
> On 23/05/18 12:00, Oleksandr Andrushchenko wrote:
> > On 05/23/2018 12:19 PM, Juergen Gross wrote:
> > > On 21/05/18 09:39, Oleksandr Andrushchenko wrote:
> > > > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > > >
> > > > Building for a 32-bit target results in warnings from casting
> > > > between a 32-bit pointer and a 64-bit integer. Fix the warnings
> > > > by casting those pointers to uintptr_t first.
> > > >
> > > > Signed-off-by: Oleksandr Andrushchenko
> > > > <oleksandr_andrushchenko@xxxxxxxx>
> > > > ---
> > > >    drivers/gpu/drm/xen/xen_drm_front.h       | 4 ++--
> > > >    drivers/gpu/drm/xen/xen_drm_front_shbuf.c | 2 +-
> > > >    2 files changed, 3 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/xen/xen_drm_front.h
> > > > b/drivers/gpu/drm/xen/xen_drm_front.h
> > > > index 2c2479b571ae..8e15dbebc4ba 100644
> > > > --- a/drivers/gpu/drm/xen/xen_drm_front.h
> > > > +++ b/drivers/gpu/drm/xen/xen_drm_front.h
> > > > @@ -126,12 +126,12 @@ struct xen_drm_front_drm_info {
> > > >      static inline u64 xen_drm_front_fb_to_cookie(struct
> > > > drm_framebuffer *fb)
> > > >    {
> > > > -    return (u64)fb;
> > > > +    return (u64)(uintptr_t)fb;
> > > Do you really still need the cast to u64?
> > Indeed, I can remove (u64) now, thank you
> > > >    }
> > > >      static inline u64 xen_drm_front_dbuf_to_cookie(struct
> > > > drm_gem_object *gem_obj)
> > > >    {
> > > > -    return (u64)gem_obj;
> > > > +    return (u64)(uintptr_t)gem_obj;
> > > >    }
> > > >      int xen_drm_front_mode_set(struct xen_drm_front_drm_pipeline
> > > > *pipeline,
> > > > diff --git a/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
> > > > b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
> > > > index 8099cb343ae3..47fc93847765 100644
> > > > --- a/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
> > > > +++ b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
> > > > @@ -122,7 +122,7 @@ static void guest_calc_num_grefs(struct
> > > > xen_drm_front_shbuf *buf)
> > > >    }
> > > >      #define xen_page_to_vaddr(page) \
> > > > -        ((phys_addr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
> > > > +        ((phys_addr_t)(uintptr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
> > > phys_addr_t for a virtual address?
> > This is because the resulting value is then passed to gnttab_set_map_op/
> > gnttab_set_unmap_op which expects host address to be passed as
> > phys_addr_t addr :(
> Okay, but this means the compiler should do the necessary cast when
> you drop the cast to phys_addr_t in xen_page_to_vaddr(), as the cast
> to uintptr_t is already producing an unsigned integer value which can
> easily be promoted to more bits, right?
Right, so I can safely use:
 #define xen_page_to_vaddr(page) \
- ((phys_addr_t)(uintptr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
+               ((uintptr_t)pfn_to_kaddr(page_to_xen_pfn(page)))

> Juergen
Thank you for your time and comments,
Oleksandr

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