> -----Original Message----- > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ananyev, > Konstantin > Sent: Monday, April 04, 2016 4:35 PM > To: Kulasek, TomaszX > Cc: dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH] examples/l3fwd: fix segfault with gcc 5.x > > Hi Tomasz, > > > -----Original Message----- > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Tomasz Kulasek > > Sent: Monday, April 04, 2016 3:45 PM > > To: dev at dpdk.org > > Subject: [dpdk-dev] [PATCH] examples/l3fwd: fix segfault with gcc 5.x > > > > It seems that with gcc >5.x and -O2/-O3 optimization breaks packet > grouping > > algorithm. > > > > When last packet pointer "lp" and "pnum->u64" buffer points the same > > memory buffer, high optimization can cause unpredictable results. It seems > > that assignment of precalculated group sizes may interfere with > > initialization of new group size when lp points value inside current group > > and didn't should be changed. > > > > With gcc >5.x and optimization we cannot be sure which assignment will be > > done first, so the group size can be counted incorrectly. > > > > This patch eliminates intersection of assignment of initial group size > > (lp[0] = 1) and precalculated group sizes when gptbl[v].idx < 4. > > > > Fixes: 94c54b4158d5 ("examples/l3fwd: rework exact-match") > > > > Signed-off-by: Tomasz Kulasek <tomaszx.kulasek at intel.com> > > --- > > examples/l3fwd/l3fwd_sse.h | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/examples/l3fwd/l3fwd_sse.h b/examples/l3fwd/l3fwd_sse.h > > index f9cf50a..1afa1f0 100644 > > --- a/examples/l3fwd/l3fwd_sse.h > > +++ b/examples/l3fwd/l3fwd_sse.h > > @@ -283,9 +283,9 @@ port_groupx4(uint16_t pn[FWDSTEP + 1], uint16_t > *lp, __m128i dp1, __m128i dp2) > > > > /* if dest port value has changed. */ > > if (v != GRPMSK) { > > - lp = pnum->u16 + gptbl[v].idx; > > - lp[0] = 1; > > pnum->u64 = gptbl[v].pnum; > > + pnum->u16[FWDSTEP] = 1; > > Hmm, but FWDSTEP and gptbl[v].idx are not always equal. > Actually could you explain a bit more - what exactly is reordered by gcc 5.x, > and how to reproduce it? > i.e what sequence of input packets will trigger an error?
Hi Konstantin, I could see the issue when having two flows in one port, one going to port 0 and the other to port 1 (using Exact Match). There is no issue when there is just one flow per port, using an older gcc version (< 5.0) or using O0/O1 (and of course, using LPM). Pablo > Konstantin > > > + lp = pnum->u16 + gptbl[v].idx; > > } > > > > return lp; > > -- > > 1.7.9.5