[PATCH 0/4] clean up zero-length arrays

[Bruce Richardson]

On Tue, Jun 14, 2022 at 10:40:50AM +0100, Bruce Richardson wrote:
> On Wed, Jun 08, 2022 at 08:23:02AM -0700, Stephen Hemminger wrote:
> > On Thu,  2 Jun 2022 16:08:30 +0100
> > Bruce Richardson <bruce.richardson at intel.com> wrote:
> > 
> > > This patchset adds a coccinelle script to clean-up zero-length
> > > arrays in structures. The final patches are the result of running
> > > that script on the DPDK repository.
> > > 
> > > Bruce Richardson (4):
> > >   cocci: add script for zero-length arrays in structs
> > >   drivers: replace zero-length arrays with undimensioned ones
> > >   lib: replace zero-length arrays with undimensioned ones
> > >   app: examples: replace zero-length arrays with undimensioned ones
> > > 
> > >  app/test/test_table_tables.c                  |  2 +-
> > >  devtools/cocci/zero_length_array.cocci        | 21 +++++++++++++++
> > >  drivers/bus/dpaa/include/netcfg.h             |  4 +--
> > >  drivers/bus/vmbus/rte_vmbus_reg.h             |  4 +--
> > >  drivers/common/cnxk/roc_se.h                  |  2 +-
> > >  drivers/common/dpaax/caamflib/desc/ipsec.h    |  2 +-
> > >  drivers/common/dpaax/dpaax_iova_table.h       |  2 +-
> > >  drivers/common/mlx5/mlx5_prm.h                | 10 +++----
> > >  drivers/crypto/ipsec_mb/ipsec_mb_private.h    |  4 +--
> > >  drivers/crypto/virtio/virtio_ring.h           |  4 +--
> > >  drivers/crypto/virtio/virtqueue.h             |  2 +-
> > >  drivers/net/atlantic/hw_atl/hw_atl_utils.h    |  2 +-
> > >  drivers/net/cxgbe/clip_tbl.h                  |  2 +-
> > >  drivers/net/cxgbe/l2t.h                       |  2 +-
> > >  drivers/net/cxgbe/mps_tcam.h                  |  2 +-
> > >  drivers/net/cxgbe/smt.h                       |  2 +-
> > >  drivers/net/enic/base/vnic_devcmd.h           |  2 +-
> > >  drivers/net/hinic/hinic_pmd_tx.h              |  2 +-
> > >  drivers/net/mlx5/mlx5_tx.h                    |  2 +-
> > >  drivers/net/nfp/nfpcore/nfp_nsp.h             |  2 +-
> > >  drivers/net/virtio/virtio_ring.h              |  4 +--
> > >  drivers/net/virtio/virtio_user/vhost_kernel.c |  2 +-
> > >  drivers/net/virtio/virtio_user/vhost_vdpa.c   |  2 +-
> > >  drivers/net/virtio/virtqueue.h                |  2 +-
> > >  drivers/regex/mlx5/mlx5_rxp.h                 |  4 +--
> > >  examples/ip_reassembly/main.c                 |  2 +-
> > >  examples/ptpclient/ptpclient.c                |  4 +--
> > >  lib/cryptodev/cryptodev_pmd.h                 |  2 +-
> > >  lib/cryptodev/rte_cryptodev.h                 |  2 +-
> > >  lib/eventdev/rte_event_timer_adapter.h        |  2 +-
> > >  lib/ip_frag/ip_reassembly.h                   |  2 +-
> > >  lib/ipsec/sa.h                                |  2 +-
> > >  lib/rib/rte_rib.c                             |  2 +-
> > >  lib/rib/rte_rib6.c                            |  2 +-
> > >  lib/table/rte_swx_table_learner.c             |  4 +--
> > >  lib/table/rte_table_hash_key16.c              |  4 +--
> > >  lib/table/rte_table_hash_key32.c              |  4 +--
> > >  lib/table/rte_table_hash_key8.c               |  4 +--
> > >  lib/vhost/rte_vhost.h                         |  4 +--
> > >  40 files changed, 101 insertions(+), 54 deletions(-)
> > >  create mode 100644 devtools/cocci/zero_length_array.cocci
> > >  create mode 100644 lib/count_comments.py
> > > 
> > > --
> > > 2.34.1
> > > 
> > 
> > Bruce, looking at this commit, it looks like the underlying cause
> > of the problem with iavf was it is using array size of one
> > when flex array should be used:
> > 
> > commit b5b3ea803e4741ad6a46a38d8227c78226d9054d
> > Author: Kevin Traynor <ktraynor at redhat.com>
> > Date:   Fri Apr 17 16:43:35 2020 +0100
> > 
> >     eal/x86: ignore gcc 10 stringop-overflow warnings
> >     
> >     stringop-overflow warns when it sees a possible overflow
> >     in a string operation.
> >     
> >     In the rte_memcpy functions different branches are taken
> >     depending on the size. stringop-overflow is raised for the
> >     branches in the function where it sees the static size of the
> >     src could be overflowed.
> >     
> >     However, in reality a correct size argument and in some cases
> >     dynamic allocation would ensure that this does not happen.
> >     
> >     For example, in the case below for key, the correct path will be
> >     chosen in rte_memcpy_generic at runtime based on the size argument
> >     but as some paths in the function could lead to a cast to 32 bytes
> >     a warning is raised.
> >     
> >     In function ‘_mm256_storeu_si256’,
> >     inlined from ‘rte_memcpy_generic’
> >     at ../lib/librte_eal/common/include/arch/x86/rte_memcpy.h:315:2,
> >     inlined from ‘iavf_configure_rss_key’
> >     at ../lib/librte_eal/common/include/arch/x86/rte_memcpy.h:869:10:
> >     
> >     /usr/lib/gcc/x86_64-redhat-linux/10/include/avxintrin.h:928:8:
> >     warning: writing 32 bytes into a region of size 1 [-Wstringop-overflow=]
> >       928 |   *__P = __A;
> >           |   ~~~~~^~~~~
> >     In file included
> >     from ../drivers/net/iavf/../../common/iavf/iavf_prototype.h:10,
> >     from ../drivers/net/iavf/iavf.h:9,
> >     from ../drivers/net/iavf/iavf_vchnl.c:22:
> >     
> >     ../drivers/net/iavf/iavf_vchnl.c:
> >     In function ‘iavf_configure_rss_key’:
> >     
> >     ../drivers/net/iavf/../../common/iavf/virtchnl.h:508:5:
> >     note: at offset 0 to object ‘key’ with size 1 declared here
> >       508 |  u8 key[1];         /* RSS hash key, packed bytes */
> >           |     ^~~
> >     
> 
> I would tend to agree with your assessment. It looks like the "u8 key[1]"
> value should probably be "u8 key[]", and also in the following structure in
> the file, "u8 lut[1]" should probably be "u8 lut[]".
> 
> Adding maintainers for driver on CC
> 
> Beilei, Jingjing, 
> 
> in "common/iavf/virtchnl.h", there are quite a number of values at the end
> of structs which are defined as arrays of size 1. We suspect that many of
> these are placeholder arrays which should be given as unsigned arrays. Is
> this assessment correct?
>
s/unsigned arrays/flexible array members/ 

i.e. arrays without a given size "[]"