> The API to prepare checksum offloads mistreats L4
> checksum type enum values as self-contained flags.
>
> Turning these flag checks into enum checks causes
> warnings by GCC about possibly uninitialised IPv4
> header pointer. The issue was found to show up in
> the case of GCC versions 4.8.5 and 5.4.0, however,
> it might be the case for a wider variety of other
> versions. As GCC version 7.4.0 is not susceptible
> to the said false positive assessment, this patch
> maintains a compiler barrier for earlier versions.
>
> Fixes: 4fb7e803eb1a ("ethdev: add Tx preparation")
> Cc: Tomasz Kulasek <tomaszx.kula...@intel.com>
> Cc: sta...@dpdk.org
>
> Signed-off-by: Ivan Malov <ivan.ma...@oktetlabs.ru>
> ---
> lib/librte_net/rte_net.h | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/lib/librte_net/rte_net.h b/lib/librte_net/rte_net.h
> index 7088584..fb09431 100644
> --- a/lib/librte_net/rte_net.h
> +++ b/lib/librte_net/rte_net.h
> @@ -151,7 +151,19 @@ uint32_t rte_net_get_ptype(const struct rte_mbuf *m,
> ipv4_hdr->hdr_checksum = 0;
> }
>
As I remember, saw something similar before...
Probably the eaiser way to overcome it, is just to always initialize ipv4_hdr
above,
something like:
+ipv4_hdr = NULL;
if (ol_flags & PKT_TX_IPV4) {
ipv4_hdr = rte_pktmbuf_mtod_offset(m, struct rte_ipv4_hdr *,
inner_l3_offset);
if (ol_flags & PKT_TX_IP_CKSUM)
ipv4_hdr->hdr_checksum = 0;
}
> - if ((ol_flags & PKT_TX_UDP_CKSUM) == PKT_TX_UDP_CKSUM) {
> +#ifdef GCC_VERSION
> +#if GCC_VERSION < 70400
> + /*
> + * Earlier versions of GCC suspect access to possibly
> + * uninitialised ipv4_hdr in the code below, although
> + * the said variable is properly initialised above.
> + * Use compiler barrier to cope with the problem.
> + */
> + rte_compiler_barrier();
> +#endif
> +#endif
> +
> + if ((ol_flags & PKT_TX_L4_MASK) == PKT_TX_UDP_CKSUM) {
> if (ol_flags & PKT_TX_IPV4) {
> udp_hdr = (struct rte_udp_hdr *)((char *)ipv4_hdr +
> m->l3_len);
> @@ -167,7 +179,7 @@ uint32_t rte_net_get_ptype(const struct rte_mbuf *m,
> udp_hdr->dgram_cksum = rte_ipv6_phdr_cksum(ipv6_hdr,
> ol_flags);
> }
> - } else if ((ol_flags & PKT_TX_TCP_CKSUM) ||
> + } else if ((ol_flags & PKT_TX_L4_MASK) == PKT_TX_TCP_CKSUM ||
> (ol_flags & PKT_TX_TCP_SEG)) {
> if (ol_flags & PKT_TX_IPV4) {
> /* non-TSO tcp or TSO */
> --
> 1.8.3.1
