Re: [dpdk-dev] [PATCH v2 2/4] mempool/octeontx2: fix build for gcc O1 optimization

[Jerin Jacob <jerinjacobk@gmail.com>]

On Fri, May 8, 2020 at 10:16 PM Ferruh Yigit <ferruh.yigit@intel.com> wrote:
>
> Can be reproduced with "make EXTRA_CFLAGS='-O1'" command using
> gcc (GCC) 9.3.1 20200408 (Red Hat 9.3.1-2)
>
> Build error:
> In file included from .../drivers/mempool/octeontx2/otx2_mempool.h:13,
>                 from .../drivers/mempool/octeontx2/otx2_mempool_ops.c:8:
> .../drivers/mempool/octeontx2/otx2_mempool_ops.c:
>         In function ‘otx2_npa_alloc’:
> .../drivers/common/octeontx2/otx2_common.h:94:2:
>     error: ‘aura_handle’ may be used uninitialized in this function
>            [-Werror=maybe-uninitialized]
>    94 |  rte_log(RTE_LOG_DEBUG, otx2_logtype_ ## subsystem,  \
>       |  ^~~~~~~
> .../drivers/mempool/octeontx2/otx2_mempool_ops.c:643:11:
>     note: ‘aura_handle’ was declared here
>   643 |  uint64_t aura_handle;
>       |           ^~~~~~~~~~~
>
> This looks like false positive, assigning an initial value to
> 'aura_handle' to fix the build error.
>
> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
> ---
> This is assuming assigning initial value won't have a performance affect
> if it does, we need to find another fix.
> And overall not sure why this false positive warning is generated.
> ---
>  drivers/mempool/octeontx2/otx2_mempool_ops.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mempool/octeontx2/otx2_mempool_ops.c b/drivers/mempool/octeontx2/otx2_mempool_ops.c
> index 162b7f01da..078ffac3e2 100644
> --- a/drivers/mempool/octeontx2/otx2_mempool_ops.c
> +++ b/drivers/mempool/octeontx2/otx2_mempool_ops.c
> @@ -640,7 +640,7 @@ otx2_npa_alloc(struct rte_mempool *mp)
>         struct otx2_npa_lf *lf;
>         struct npa_aura_s aura;
>         struct npa_pool_s pool;
> -       uint64_t aura_handle;
> +       uint64_t aura_handle = 0;

It is a false positive. Since it is on a slow path, This workaround is OK.
While merging t this patch, Could you move "uint64_t aura_handle = 0;"
just before "struct otx2_npa_lf *lf" as
the variables are ordered in reverse xmas tree format in this file.

With the above change:
Acked-by: Jerin Jacob <jerinj@marvell.com>


>         size_t padding;
>         int rc;
>
> --
> 2.25.4
>