[dpdk-stable] [dpdk-dev] [PATCH v2] mbuf: replace zero-length marker with unnamed union
Stephen Hemminger
stephen at networkplumber.org
Mon Mar 9 16:47:32 CET 2020
On Mon, 9 Mar 2020 08:55:05 +0000
Ferruh Yigit <ferruh.yigit at intel.com> wrote:
> On 3/7/2020 3:56 PM, Gavin Hu wrote:
> > Declaring zero-length arrays in other contexts, including as interior
> > members of structure objects or as non-member objects, is discouraged.
> > Accessing elements of zero-length arrays declared in such contexts is
> > undefined and may be diagnosed.[1]
> >
> > Fix by using unnamed union and struct.
> >
> > https://bugs.dpdk.org/show_bug.cgi?id=396
> >
> > Bugzilla ID: 396
> >
> > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> >
> > Fixes: 3e6181b07038 ("mbuf: use structure marker from EAL")
> > Cc: stable at dpdk.org
> >
> > Signed-off-by: Gavin Hu <gavin.hu at arm.com>
> > ---
> > v2:
> > * change 'uint64_t rearm_data' to 'uint_64_t rearm_data[1]' to fix
> > the SFC PMD compiling error on x86. <Kevin Traynor>
> > ---
> > lib/librte_mbuf/rte_mbuf_core.h | 54 +++++++++++++++++++--------------
> > 1 file changed, 32 insertions(+), 22 deletions(-)
> >
> > diff --git a/lib/librte_mbuf/rte_mbuf_core.h b/lib/librte_mbuf/rte_mbuf_core.h
> > index b9a59c879..34cb152e2 100644
> > --- a/lib/librte_mbuf/rte_mbuf_core.h
> > +++ b/lib/librte_mbuf/rte_mbuf_core.h
> > @@ -480,31 +480,41 @@ struct rte_mbuf {
> > rte_iova_t buf_physaddr; /**< deprecated */
> > } __rte_aligned(sizeof(rte_iova_t));
> >
> > - /* next 8 bytes are initialised on RX descriptor rearm */
> > - RTE_MARKER64 rearm_data;
> > - uint16_t data_off;
> > -
> > - /**
> > - * Reference counter. Its size should at least equal to the size
> > - * of port field (16 bits), to support zero-copy broadcast.
> > - * It should only be accessed using the following functions:
> > - * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and
> > - * rte_mbuf_refcnt_set(). The functionality of these functions (atomic,
> > - * or non-atomic) is controlled by the CONFIG_RTE_MBUF_REFCNT_ATOMIC
> > - * config option.
> > - */
> > RTE_STD_C11
> > union {
> > - rte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */
> > - /** Non-atomically accessed refcnt */
> > - uint16_t refcnt;
> > - };
> > - uint16_t nb_segs; /**< Number of segments. */
> > + /* next 8 bytes are initialised on RX descriptor rearm */
> > + uint64_t rearm_data[1];
> We are using zero length array as markers only and know what we are doing with them,
> what would you think disabling the warning instead of increasing the complexity
> in mbuf struct?
No to disabling warnings.
Or get rid of the markers all together, the usage is awkward already.
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