| Message ID | 20180918050123.27641-1-blp@ovn.org |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [ovs-dev] util: Better document ALIGNED_CAST. | expand |
On Mon, Sep 17, 2018 at 10:01 PM Ben Pfaff <blp@ovn.org> wrote: > > CC: Han Zhou <zhouhan@gmail.com> > Signed-off-by: Ben Pfaff <blp@ovn.org> > --- > include/openvswitch/util.h | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/include/openvswitch/util.h b/include/openvswitch/util.h > index b4d49ee21804..9189e6480b1c 100644 > --- a/include/openvswitch/util.h > +++ b/include/openvswitch/util.h > @@ -273,8 +273,14 @@ is_pow2(uintmax_t x) > #define BITMAP_ULONG_BITS (sizeof(unsigned long) * CHAR_BIT) > #define BITMAP_N_LONGS(N_BITS) DIV_ROUND_UP(N_BITS, BITMAP_ULONG_BITS) > > -/* Given ATTR, and TYPE, cast the ATTR to TYPE by first casting ATTR to > - * (void *). This is to suppress the alignment warning issued by clang. */ > +/* Given ATTR, and TYPE, cast the ATTR to TYPE by first casting ATTR to (void > + * *). This suppresses the alignment warning issued by Clang and newer > + * versions of GCC when a pointer is cast to a type with a stricter alignment. > + * > + * Add ALIGNED_CAST only if you are sure that the cast is actually correct, > + * that is, that the pointer is actually properly aligned for the stricter > + * type. On RISC architectures, dereferencing a misaligned pointer can cause a > + * segfault, so it is important to be aware of correct alignment. */ > #define ALIGNED_CAST(TYPE, ATTR) ((TYPE) (void *) (ATTR)) > > #ifdef __cplusplus > -- > 2.16.1 > Thanks Ben. Acked-by: Han Zhou <hzhou8@ebay.com>
On Mon, Sep 17, 2018 at 10:12:09PM -0700, Han Zhou wrote: > On Mon, Sep 17, 2018 at 10:01 PM Ben Pfaff <blp@ovn.org> wrote: > > > > CC: Han Zhou <zhouhan@gmail.com> > > Signed-off-by: Ben Pfaff <blp@ovn.org> > > --- > > include/openvswitch/util.h | 10 ++++++++-- > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > diff --git a/include/openvswitch/util.h b/include/openvswitch/util.h > > index b4d49ee21804..9189e6480b1c 100644 > > --- a/include/openvswitch/util.h > > +++ b/include/openvswitch/util.h > > @@ -273,8 +273,14 @@ is_pow2(uintmax_t x) > > #define BITMAP_ULONG_BITS (sizeof(unsigned long) * CHAR_BIT) > > #define BITMAP_N_LONGS(N_BITS) DIV_ROUND_UP(N_BITS, BITMAP_ULONG_BITS) > > > > -/* Given ATTR, and TYPE, cast the ATTR to TYPE by first casting ATTR to > > - * (void *). This is to suppress the alignment warning issued by clang. > */ > > +/* Given ATTR, and TYPE, cast the ATTR to TYPE by first casting ATTR to > (void > > + * *). This suppresses the alignment warning issued by Clang and newer > > + * versions of GCC when a pointer is cast to a type with a stricter > alignment. > > + * > > + * Add ALIGNED_CAST only if you are sure that the cast is actually > correct, > > + * that is, that the pointer is actually properly aligned for the > stricter > > + * type. On RISC architectures, dereferencing a misaligned pointer can > cause a > > + * segfault, so it is important to be aware of correct alignment. */ > > #define ALIGNED_CAST(TYPE, ATTR) ((TYPE) (void *) (ATTR)) > > > > #ifdef __cplusplus > > -- > > 2.16.1 > > > > Thanks Ben. > Acked-by: Han Zhou <hzhou8@ebay.com> Thanks, applied to master.
diff --git a/include/openvswitch/util.h b/include/openvswitch/util.h index b4d49ee21804..9189e6480b1c 100644 --- a/include/openvswitch/util.h +++ b/include/openvswitch/util.h @@ -273,8 +273,14 @@ is_pow2(uintmax_t x) #define BITMAP_ULONG_BITS (sizeof(unsigned long) * CHAR_BIT) #define BITMAP_N_LONGS(N_BITS) DIV_ROUND_UP(N_BITS, BITMAP_ULONG_BITS) -/* Given ATTR, and TYPE, cast the ATTR to TYPE by first casting ATTR to - * (void *). This is to suppress the alignment warning issued by clang. */ +/* Given ATTR, and TYPE, cast the ATTR to TYPE by first casting ATTR to (void + * *). This suppresses the alignment warning issued by Clang and newer + * versions of GCC when a pointer is cast to a type with a stricter alignment. + * + * Add ALIGNED_CAST only if you are sure that the cast is actually correct, + * that is, that the pointer is actually properly aligned for the stricter + * type. On RISC architectures, dereferencing a misaligned pointer can cause a + * segfault, so it is important to be aware of correct alignment. */ #define ALIGNED_CAST(TYPE, ATTR) ((TYPE) (void *) (ATTR)) #ifdef __cplusplus
CC: Han Zhou <zhouhan@gmail.com> Signed-off-by: Ben Pfaff <blp@ovn.org> --- include/openvswitch/util.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)