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SubjectRe: [PATCH] IB/core: Replace zero-length array with flexible-array member
On Thu, Feb 13, 2020 at 12:37:15PM -0600, Gustavo A. R. Silva wrote:
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
>
> struct foo {
> int stuff;
> struct boo array[];
> };
>
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
>
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
>
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
>
> This issue was found with the help of Coccinelle.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> drivers/infiniband/core/cache.c | 2 +-
> drivers/infiniband/core/cm.c | 4 ++--
> drivers/infiniband/core/multicast.c | 2 +-
> drivers/infiniband/core/sa_query.c | 2 +-
> 4 files changed, 5 insertions(+), 5 deletions(-)

Any reason to skip these two?

drivers/infiniband/core/mad_priv.h: u8 mad[0];
drivers/infiniband/core/mad_priv.h: u8 data[0];

And may as well touch these in the subsystem headers too:

include/rdma/ib_fmr_pool.h: u64 page_list[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/ib_verbs.h: u8 real_sz[0];
include/rdma/opa_vnic.h: char *dev_priv[0];
include/rdma/rdmavt_mr.h: struct rvt_segarray *map[0]; /* the segments */
include/rdma/rdmavt_qp.h: struct rvt_sge sg_list[0];

?

Jason

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