Re: [PATCH] eventdev: fix symbol export for port maintenance

[David Marchand <david.marchand@redhat.com>]

Jerin,

On Wed, Oct 11, 2023 at 9:03 AM David Marchand
<david.marchand@redhat.com> wrote:
>
> On Wed, Oct 11, 2023 at 8:47 AM Mattias Rönnblom <hofors@lysator.liu.se> wrote:
> >
> > On 2023-10-10 16:00, David Marchand wrote:
> > > Trying to call rte_event_maintain out of the eventdev library triggers
> > > a link failure, as the tracepoint symbol associated to this inline
> > > helper was not exported.
> > >
> > > Fixes: 54f17843a887 ("eventdev: add port maintenance API")
> > > Cc: stable@dpdk.org
> > >
> > > Signed-off-by: David Marchand <david.marchand@redhat.com>
> > > ---
> > > Caught by the CI when testing the dispatcher library.
> > > See for example:
> > > https://github.com/ovsrobot/dpdk/actions/runs/6460514355/job/17538348529#step:19:5506
> > >
> > > ---
> > >   lib/eventdev/version.map | 1 +
> > >   1 file changed, 1 insertion(+)
> > >
> > > diff --git a/lib/eventdev/version.map b/lib/eventdev/version.map
> > > index b03c10d99f..249eb115b1 100644
> > > --- a/lib/eventdev/version.map
> > > +++ b/lib/eventdev/version.map
> > > @@ -5,6 +5,7 @@ DPDK_24 {
> > >       __rte_eventdev_trace_deq_burst;
> > >       __rte_eventdev_trace_enq_burst;
> > >       __rte_eventdev_trace_eth_tx_adapter_enqueue;
> > > +     __rte_eventdev_trace_maintain;
> > >       __rte_eventdev_trace_timer_arm_burst;
> > >       __rte_eventdev_trace_timer_arm_tmo_tick_burst;
> > >       __rte_eventdev_trace_timer_cancel_burst;
> >
> > I can't say I know why it's needed, but the change seems consistent with
> > other Eventdev trace points.
>
> The trace point framework in DPDK relies on a per trace point global
> variable (whose name is __<trace point name>):
>
> #define __RTE_TRACE_POINT(_mode, _tp, _args, ...) \
> extern rte_trace_point_t __##_tp; \
> static __rte_always_inline void \
> _tp _args \
> { \
>         __rte_trace_point_emit_header_##_mode(&__##_tp); \
>         __VA_ARGS__ \
> }
>
> When tracepoints are called from within a shared library code, and
> because all symbols of a group of objects are visible, the tracepoint
> symbols are resolved by the linker.
> But when this tracepoint is called via an inline helper from some code
> out of the shared library, this symbol must be exported in the shared
> library map or it won't be visible to "external" users.

Could we describe / mention this in the trace point library doc?
Or maybe I read too quickly and there is already something but it was
not obvious to me.


-- 
David Marchand