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

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Date:   Mon, 28 Mar 2022 15:53:38 -0700
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Jiri Olsa <olsajiri@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Delyan Kratunov <delyank@...com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Networking <netdev@...r.kernel.org>, bpf <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 2:31 PM, Andrii Nakryiko wrote:
> On Mon, Mar 28, 2022 at 11:50 AM Jiri Olsa <olsajiri@...il.com> wrote:
>>
>> On Mon, Mar 28, 2022 at 08:41:18AM -0700, Yonghong Song wrote:
>>>
>>>
>>> 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?
>>
>> good point, will check
> 
> we can use this function for some more assertions in the future, so
> instead of trying to be smart about generating or not of this
> function, I think unused attribute is a more robust solution.

Okay, if there are possibly more assertions down the road,
I am fine to keep the function even if it is empty to avoid
more and more conditions to decide whether the functions
should be generated at all.

> 
>>
>> jirka
>>
>>>
>>>>
>>>> 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\