[dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping

[dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping

[Guduri Prathyusha]

With -f-strict-aliasing enabled by default from -O2, gcc > 5.x gives
undefined behavior in port_groupx4 in ARM. 'pn' and 'pnum' are
two different pointers pointing to same chunk of memory and
with -f-strict-aliasing the pointers are assumed to be pointing to
different memory and compiler reorders instructions that depend on
pnum and pn. This breaks port grouping algorithm.

This patch eliminates the above problem by introducing a compiler
barrier between the instructions that depend on pnum, pn and lp.

Fixes: 569b290cdb36 ("examples/l3fwd: add NEON implementation")

Signed-off-by: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
---
 examples/l3fwd/l3fwd_neon.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/examples/l3fwd/l3fwd_neon.h b/examples/l3fwd/l3fwd_neon.h
index 4bc161394..b319b5a92 100644
--- a/examples/l3fwd/l3fwd_neon.h
+++ b/examples/l3fwd/l3fwd_neon.h
@@ -114,6 +114,7 @@ port_groupx4(uint16_t pn[FWDSTEP + 1], uint16_t *lp, uint16x8_t dp1,
 
 	/* update last port counter. */
 	lp[0] += gptbl[v].lpv;
+	rte_compiler_barrier();
 
 	/* if dest port value has changed. */
 	if (v != GRPMSK) {
-- 
2.14.1

Re: [dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping

[Jerin Jacob]

-----Original Message-----
> Date: Fri,  3 Nov 2017 16:13:51 +0530
> From: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
> To: tomasz.kantecki@intel.com
> CC: Jianbo.Liu@arm.com, guduriprathyusha@gmail.com,
>  konstantin.ananyev@intel.com, dev@dpdk.org, Guduri Prathyusha
>  <gprathyusha@caviumnetworks.com>
> Subject: [dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping
> X-Mailer: git-send-email 2.14.1
> 
> With -f-strict-aliasing enabled by default from -O2, gcc > 5.x gives
> undefined behavior in port_groupx4 in ARM. 'pn' and 'pnum' are
> two different pointers pointing to same chunk of memory and
> with -f-strict-aliasing the pointers are assumed to be pointing to
> different memory and compiler reorders instructions that depend on
> pnum and pn. This breaks port grouping algorithm.
> 
> This patch eliminates the above problem by introducing a compiler
> barrier between the instructions that depend on pnum, pn and lp.
> 
> Fixes: 569b290cdb36 ("examples/l3fwd: add NEON implementation")
> 
> Signed-off-by: Guduri Prathyusha <gprathyusha@caviumnetworks.com>

Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>

> ---
>  examples/l3fwd/l3fwd_neon.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/examples/l3fwd/l3fwd_neon.h b/examples/l3fwd/l3fwd_neon.h
> index 4bc161394..b319b5a92 100644
> --- a/examples/l3fwd/l3fwd_neon.h
> +++ b/examples/l3fwd/l3fwd_neon.h
> @@ -114,6 +114,7 @@ port_groupx4(uint16_t pn[FWDSTEP + 1], uint16_t *lp, uint16x8_t dp1,
>  
>  	/* update last port counter. */
>  	lp[0] += gptbl[v].lpv;
> +	rte_compiler_barrier();
>  
>  	/* if dest port value has changed. */
>  	if (v != GRPMSK) {
> -- 
> 2.14.1
> 

Re: [dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping

[Jianbo Liu]

The 11/06/2017 09:59, Jerin Jacob wrote:
> -----Original Message-----
> > Date: Fri,  3 Nov 2017 16:13:51 +0530
> > From: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
> > To: tomasz.kantecki@intel.com
> > CC: Jianbo.Liu@arm.com, guduriprathyusha@gmail.com,
> >  konstantin.ananyev@intel.com, dev@dpdk.org, Guduri Prathyusha
> >  <gprathyusha@caviumnetworks.com>
> > Subject: [dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping
> > X-Mailer: git-send-email 2.14.1
> >
> > With -f-strict-aliasing enabled by default from -O2, gcc > 5.x gives
> > undefined behavior in port_groupx4 in ARM. 'pn' and 'pnum' are
> > two different pointers pointing to same chunk of memory and
> > with -f-strict-aliasing the pointers are assumed to be pointing to
> > different memory and compiler reorders instructions that depend on
> > pnum and pn. This breaks port grouping algorithm.
> >
> > This patch eliminates the above problem by introducing a compiler
> > barrier between the instructions that depend on pnum, pn and lp.
> >
> > Fixes: 569b290cdb36 ("examples/l3fwd: add NEON implementation")
> >
> > Signed-off-by: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
>
> Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
>

Acked-by: Jianbo Liu <jianbo.liu@arm.com>
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Re: [dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping

[Ferruh Yigit]

On 11/6/2017 12:18 AM, Jianbo Liu wrote:
> The 11/06/2017 09:59, Jerin Jacob wrote:
>> -----Original Message-----
>>> Date: Fri,  3 Nov 2017 16:13:51 +0530
>>> From: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
>>> To: tomasz.kantecki@intel.com
>>> CC: Jianbo.Liu@arm.com, guduriprathyusha@gmail.com,
>>>  konstantin.ananyev@intel.com, dev@dpdk.org, Guduri Prathyusha
>>>  <gprathyusha@caviumnetworks.com>
>>> Subject: [dpdk-dev] [PATCH v2] examples/l3fwd: fix aliasing in port grouping
>>> X-Mailer: git-send-email 2.14.1
>>>
>>> With -f-strict-aliasing enabled by default from -O2, gcc > 5.x gives
>>> undefined behavior in port_groupx4 in ARM. 'pn' and 'pnum' are
>>> two different pointers pointing to same chunk of memory and
>>> with -f-strict-aliasing the pointers are assumed to be pointing to
>>> different memory and compiler reorders instructions that depend on
>>> pnum and pn. This breaks port grouping algorithm.
>>>
>>> This patch eliminates the above problem by introducing a compiler
>>> barrier between the instructions that depend on pnum, pn and lp.
>>>
>>> Fixes: 569b290cdb36 ("examples/l3fwd: add NEON implementation")
>>>
>>> Signed-off-by: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
>>
>> Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> 
> Acked-by: Jianbo Liu <jianbo.liu@arm.com>

Applied to dpdk/master, thanks.