netdev - Re: [PATCH] bpftool: Fix generated code in codegen

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Date:   Mon, 28 Mar 2022 08:41:18 -0700
From:   Yonghong Song <yhs@...com>
To:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Delyan Kratunov <delyank@...com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH] bpftool: Fix generated code in codegen_asserts



On 3/28/22 1:37 AM, Jiri Olsa wrote:
> Arnaldo reported perf compilation fail with:
> 
>    $ make -k BUILD_BPF_SKEL=1 CORESIGHT=1 PYTHON=python3
>    ...
>    In file included from util/bpf_counter.c:28:
>    /tmp/build/perf//util/bpf_skel/bperf_leader.skel.h: In function ‘bperf_leader_bpf__assert’:
>    /tmp/build/perf//util/bpf_skel/bperf_leader.skel.h:351:51: error: unused parameter ‘s’ [-Werror=unused-parameter]
>      351 | bperf_leader_bpf__assert(struct bperf_leader_bpf *s)
>          |                          ~~~~~~~~~~~~~~~~~~~~~~~~~^
>    cc1: all warnings being treated as errors
> 
> If there's nothing to generate in the new assert function,
> we will get unused 's' warn/error, adding 'unused' attribute to it.

If there is nothing to generate, should we avoid generating
the assert function itself?

> 
> Cc: Delyan Kratunov <delyank@...com>
> Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Fixes: 08d4dba6ae77 ("bpftool: Bpf skeletons assert type sizes")
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>   tools/bpf/bpftool/gen.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 7ba7ff55d2ea..91af2850b505 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -477,7 +477,7 @@ static void codegen_asserts(struct bpf_object *obj, const char *obj_name)
>   	codegen("\
>   		\n\
>   		__attribute__((unused)) static void			    \n\
> -		%1$s__assert(struct %1$s *s)				    \n\
> +		%1$s__assert(struct %1$s *s __attribute__((unused)))	    \n\
>   		{							    \n\
>   		#ifdef __cplusplus					    \n\
>   		#define _Static_assert static_assert			    \n\