> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Monday, June 24, 2019 12:52 PM
> To: 'Ivan Malov' <ivan.ma...@oktetlabs.ru>; Olivier Matz
> <olivier.m...@6wind.com>
> Cc: dev@dpdk.org; Kulasek, TomaszX <tomaszx.kula...@intel.com>;
> sta...@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH] net: fix the way how L4 checksum choice is
> tested
>
>
> > 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;
> }
As another possible option always initialisze both, and then use either one or
another,
depending on flags:
ipv4_hdr = rte_pktmbuf_mtod_offset(m, struct rte_ipv4_hdr *, inner_l3_offset);
ipv6_hdr = rte_pktmbuf_mtod_offset(m, struct rte_ipv6_hdr *, inner_l3_offset);
....
>
>
> > - 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
