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

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

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.


-- 
David Marchand