Re: [PATCH] RDMA/cxgb4: Replace 0-length arrays with flexible arrays

Kees Cook
2023-01-14T01:03:56Z

On Sun, Jan 08, 2023 at 02:08:52PM +0200, Leon Romanovsky wrote:
> On Thu, Jan 05, 2023 at 02:32:32PM -0800, Kees Cook wrote:
> > Zero-length arrays are deprecated[1]. Replace all remaining
> > 0-length arrays with flexible arrays. Detected with GCC 13, using
> > -fstrict-flex-arrays=3:
> >
> > In function 'build_rdma_write',
> > inlined from 'c4iw_post_send' at ../drivers/infiniband/hw/cxgb4/qp.c:1173:10:
> > ../drivers/infiniband/hw/cxgb4/qp.c:597:38: warning: array subscript 0 is outside array bounds of 'struct fw_ri_immd[0]' [-Warray-bounds=]
> > 597 | wqe->write.u.immd_src[0].r2 = 0;
> > | ~~~~~~~~~~~~~~~~~~~~~^~~
> > ../drivers/infiniband/hw/cxgb4/t4fw_ri_api.h: In function 'c4iw_post_send':
> > ../drivers/infiniband/hw/cxgb4/t4fw_ri_api.h:567:35: note: while referencing 'immd_src'
> > 567 | struct fw_ri_immd immd_src[0];
> > | ^~~~~~~~
> >
> > Additionally drop the unused C99_NOT_SUPPORTED ifndef lines.
> >
> > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
> >
> > Cc: Potnuri Bharat Teja <bharat@chelsio.com>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: Leon Romanovsky <leon@kernel.org>
> > Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> > Cc: linux-rdma@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> > drivers/infiniband/hw/cxgb4/t4fw_ri_api.h | 26 ++++++-----------------
> > 1 file changed, 6 insertions(+), 20 deletions(-)
>
> <...>
>
> > #define FW_RI_SEND_WR_SENDOP_S 0
> > @@ -618,12 +606,10 @@ struct fw_ri_rdma_write_cmpl_wr {
> > struct fw_ri_isgl isgl_src;
> > } u_cmpl;
> > __be64 r3;
> > -#ifndef C99_NOT_SUPPORTED
> > union fw_ri_write {
> > - struct fw_ri_immd immd_src[0];
> > - struct fw_ri_isgl isgl_src[0];
> > + DECLARE_FLEX_ARRAY(struct fw_ri_immd, immd_src);
> > + DECLARE_FLEX_ARRAY(struct fw_ri_isgl, isgl_src);
>
> smatch built from commit 40351132df3b ("strlen: add __builtin and
> __fortify functions") produces the following warning:
> drivers/infiniband/hw/cxgb4/t4fw_ri_api.h:575:17: warning: array of flexible structures
>
> Is it expected? What will prevent from getting this warning from 0-day
> build bots?

Err, I'm not sure I understand? Does smatch define "C99_NOT_SUPPORTED"?

--
Kees Cook