On Mon, Jul 26, 2021 at 5:04 PM Sven Eckelmann sven@narfation.org 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=1I 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