[dpdk-dev] DPDK compilation on arm is failing in Travis

[Honnappa Nagarahalli]

> 
> Thomas Monjalon <thomas at monjalon.net> writes:
> 
> > 05/06/2019 21:40, Aaron Conole:
> >> Thomas Monjalon <thomas at monjalon.net> writes:
> >>
> >> > The compilation of the master branch is failing for aarch64:
> >> > 	https://travis-ci.com/DPDK/dpdk
> >> > The log is so much verbose that I am not able to understand what is
> >> > really wrong.
> >> > Please help to diagnose and fix, thanks.
> >>
> >> A discussion about this:
> >>
> >> http://mails.dpdk.org/archives/dev/2019-June/134012.html
> >
> > I see the error now.
> > It is printing the full log after the error, so I missed the error at
> > the top.
> >
> > I've read your comment about a possible error with the patch removing
> > weak functions but neither me nor Bruce were able to reproduce it.
> > What is the condition to see this compiler warning?
> 
> It is only on ARM, and only when the neon intrinsics are in use.
I am not able to reproduce it from the tip of master.

I am using:
gcc (Ubuntu 8.3.0-6ubuntu1~18.04) 8.3.0

>From the log on Travis, looks like the compiler is:
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.11) 5.4.0 20160609

Is this the issue?

Why are we seeing the error now?

> 
> The issue is the vector lane setting code looks like:
> 
>    lval = lane_set(scalar, rval, lane id)
> 
> In this case, 'rval' is being used before it is ever set, but it really could be just 0
> for the first lane setting code.  Thereafter, we use the old value of input as the
> rval, but each time a different lane is set.
> 
> It would be nice if there were an intrinsic that formatted correctly from the
> start (something we could call like lval = lane_set_from_array(scalar_array)).
> Then 'input' would never appear as an rval before it was set.
> 
> I thought Jerin Jacob (CC'd) would have some opinion on the right fix.
> There are three 'fixes' I know exist - one is to squelch the warning (but I don't
> like it because it could hide future code that introduces this), one is to create a
> static and use assignment, one is to replace the first call and pass in a 0'd lane
> for the first one.
> 
> Actually, I think I have a patch that could work to not introduce an assignment,
> but squelch the warning.  Something like the following (not tested).
> 
> ---
> 
> diff --git a/lib/librte_acl/acl_run_neon.h b/lib/librte_acl/acl_run_neon.h index
> 01b9766d8..37c984fef 100644
> --- a/lib/librte_acl/acl_run_neon.h
> +++ b/lib/librte_acl/acl_run_neon.h
> @@ -165,6 +165,7 @@ search_neon_8(const struct rte_acl_ctx *ctx, const
> uint8_t **data,
>  	uint64_t index_array[8];
>  	struct completion cmplt[8];
>  	struct parms parms[8];
> +	static int32x4_t ZEROVAL;
>  	int32x4_t input0, input1;
> 
>  	acl_set_flow(&flows, cmplt, RTE_DIM(cmplt), data, results, @@ -
> 181,8 +182,8 @@ search_neon_8(const struct rte_acl_ctx *ctx, const uint8_t
> **data,
> 
>  	while (flows.started > 0) {
>  		/* Gather 4 bytes of input data for each stream. */
> -		input0 = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 0), input0,
> 0);
> -		input1 = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 4), input1,
> 0);
> +		input0 = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 0),
> ZEROVAL, 0);
> +		input1 = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 4),
> ZEROVAL, 0);
> 
>  		input0 = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 1), input0,
> 1);
>  		input1 = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 5), input1,
> 1); @@ -227,6 +228,7 @@ search_neon_4(const struct rte_acl_ctx *ctx, const
> uint8_t **data,
>  	uint64_t index_array[4];
>  	struct completion cmplt[4];
>  	struct parms parms[4];
> +	static int32x4_t ZEROVAL;
>  	int32x4_t input;
> 
>  	acl_set_flow(&flows, cmplt, RTE_DIM(cmplt), data, results, @@ -
> 242,7 +244,7 @@ search_neon_4(const struct rte_acl_ctx *ctx, const uint8_t
> **data,
> 
>  	while (flows.started > 0) {
>  		/* Gather 4 bytes of input data for each stream. */
> -		input = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 0), input, 0);
> +		input = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 0),
> ZEROVAL, 0);
>  		input = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 1), input, 1);
>  		input = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 2), input, 2);
>  		input = vsetq_lane_s32(GET_NEXT_4BYTES(parms, 3), input, 3);
> --
> 2.21.0