From: Arnd Bergmann <arnd@arndb.de>
To: Sven Eckelmann <sven@narfation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Arnd Bergmann <arnd@arndb.de>,
b.a.t.m.a.n@lists.open-mesh.org,
linux-arch <linux-arch@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] asm-generic: avoid sparse {get,put}_unaligned warning
Date: Mon, 26 Jul 2021 18:22:02 +0200 [thread overview]
Message-ID: <CAK8P3a35PNhsMQNU11RCaKm-o3-oG8pOXG836aoubxQMpTyVNQ@mail.gmail.com> (raw)
In-Reply-To: <3234493.RMHOAZ7QyG@ripper>
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=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
next prev parent reply other threads:[~2021-07-26 16:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-24 16:24 [PATCH] asm-generic: avoid sparse {get,put}_unaligned warning Sven Eckelmann
2021-07-24 17:01 ` Al Viro
2021-07-26 12:57 ` Arnd Bergmann
2021-07-26 15:04 ` Sven Eckelmann
2021-07-26 16:22 ` Arnd Bergmann [this message]
2021-07-27 8:44 ` David Laight
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