linux-kernel - Re: [PATCH] neighbor: tracing: Move pin6 inside CONFIG

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Date:   Tue, 17 Oct 2023 11:59:47 +0200
From:   Simon Horman <horms@...nel.org>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>,
        linux-trace-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] neighbor: tracing: Move pin6 inside CONFIG_IPV6=y section

On Mon, Oct 16, 2023 at 02:49:04PM +0200, Geert Uytterhoeven wrote:
> When CONFIG_IPV6=n, and building with W=1:
> 
>     In file included from include/trace/define_trace.h:102,
> 		     from include/trace/events/neigh.h:255,
> 		     from net/core/net-traces.c:51:
>     include/trace/events/neigh.h: In function ‘trace_event_raw_event_neigh_create’:
>     include/trace/events/neigh.h:42:34: error: variable ‘pin6’ set but not used [-Werror=unused-but-set-variable]
>        42 |                 struct in6_addr *pin6;
> 	  |                                  ^~~~
>     include/trace/trace_events.h:402:11: note: in definition of macro ‘DECLARE_EVENT_CLASS’
>       402 |         { assign; }                                                     \
> 	  |           ^~~~~~
>     include/trace/trace_events.h:44:30: note: in expansion of macro ‘PARAMS’
>        44 |                              PARAMS(assign),                   \
> 	  |                              ^~~~~~
>     include/trace/events/neigh.h:23:1: note: in expansion of macro ‘TRACE_EVENT’
>        23 | TRACE_EVENT(neigh_create,
> 	  | ^~~~~~~~~~~
>     include/trace/events/neigh.h:41:9: note: in expansion of macro ‘TP_fast_assign’
>        41 |         TP_fast_assign(
> 	  |         ^~~~~~~~~~~~~~
>     In file included from include/trace/define_trace.h:103,
> 		     from include/trace/events/neigh.h:255,
> 		     from net/core/net-traces.c:51:
>     include/trace/events/neigh.h: In function ‘perf_trace_neigh_create’:
>     include/trace/events/neigh.h:42:34: error: variable ‘pin6’ set but not used [-Werror=unused-but-set-variable]
>        42 |                 struct in6_addr *pin6;
> 	  |                                  ^~~~
>     include/trace/perf.h:51:11: note: in definition of macro ‘DECLARE_EVENT_CLASS’
>        51 |         { assign; }                                                     \
> 	  |           ^~~~~~
>     include/trace/trace_events.h:44:30: note: in expansion of macro ‘PARAMS’
>        44 |                              PARAMS(assign),                   \
> 	  |                              ^~~~~~
>     include/trace/events/neigh.h:23:1: note: in expansion of macro ‘TRACE_EVENT’
>        23 | TRACE_EVENT(neigh_create,
> 	  | ^~~~~~~~~~~
>     include/trace/events/neigh.h:41:9: note: in expansion of macro ‘TP_fast_assign’
>        41 |         TP_fast_assign(
> 	  |         ^~~~~~~~~~~~~~
> 
> Indeed, the variable pin6 is declared and initialized unconditionally,
> while it is only used and needlessly re-initialized when support for
> IPv6 is enabled.
> 
> Fix this by dropping the unused variable initialization, and moving the
> variable declaration inside the existing section protected by a check
> for CONFIG_IPV6.
> 
> Fixes: fc651001d2c5ca4f ("neighbor: Add tracepoint to __neigh_create")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Reviewed-by: Simon Horman <horms@...nel.org>
Tested-by: Simon Horman <horms@...nel.org> # build-tested