On Mon, Jul 26, 2021 at 5:04 PM Sven Eckelmann <sven@xxxxxxxxxxxxx> wrote:
>
> On Monday, 26 July 2021 14:57:31 CEST Arnd Bergmann wrote:
> > >
> > > > The special attribute force must be used in such statements when the cast
> > > > is known to be safe to avoid these warnings.
> >
> > I can see why this would warn, but I'm having trouble reproducing the
> > warning on linux-next.
>
> I have sparse 0.6.3 on an Debian bullseye amd64 system. Sources are from
> linux-next next-20210723
>
> make allnoconfig
> cat >> .config << "EOF"
> CONFIG_NET=y
> CONFIG_INET=y
> CONFIG_BATMAN_ADV=y
> CONFIG_BATMAN_ADV_DAT=y
> EOF
> make olddefconfig
> make CHECK="sparse -Wbitwise-pointer" C=1
>
> I should maybe have made this clearer in the last sentence of the first
> paragraph: "This is also true for pointers to variables with this type when
> -Wbitwise-pointer is activated."
Ok, got it. I assumed this would be turned on by an 'allmodconfig' build.
> > If both work equally well, I'd prefer Sven's patch since that only
> > expands 'type' once, while container_of() expands it three more times
Not sure what I was thinking here, as it's not 'type' that gets expanded
here but 'ptr'. We could do Al's suggestion to avoid the __force without
multiple expansions, using
diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h
index 1c4242416c9f..d138dc5fd8e3 100644
--- a/include/asm-generic/unaligned.h
+++ b/include/asm-generic/unaligned.h
@@ -10,17 +10,25 @@
#include <asm/byteorder.h>
#define __get_unaligned_t(type, ptr) ({
\
- const struct { type x; } __packed *__pptr =
(typeof(__pptr))(ptr); \
+ const struct { type x; } __packed *__pptr =
\
+ container_of(ptr, typeof(*__pptr), x);
\
__pptr->x;
\
})
#define __put_unaligned_t(type, val, ptr) do {
\
- struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);
\
+ struct { type x; } __packed *__pptr =
\
+ container_of(ptr, typeof(*__pptr), x);
\
__pptr->x = (val);
\
} while (0)
-#define get_unaligned(ptr) __get_unaligned_t(typeof(*(ptr)), (ptr))
-#define put_unaligned(val, ptr) __put_unaligned_t(typeof(*(ptr)), (val), (ptr))
+#define get_unaligned(ptr) ({
\
+ __auto_type _ptr = (ptr);
\
+ __get_unaligned_t(typeof(*(_ptr)), (_ptr));
\
+})
+#define put_unaligned(val, ptr) ({
\
+ __auto_type _ptr = (ptr);
\
+ __put_unaligned_t(typeof(*(_ptr)), (val), (_ptr));
\
+})
static inline u16 get_unaligned_le16(const void *p)
{
Not sure if this is any better.
Arnd
