linux-kernel - Re: [PATCH] selftests/bpf: Remove unneeded variable "ret"

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Message-ID: <53510828-ee5b-1d91-0f85-b79da4422741@meta.com>
Date:   Tue, 13 Jun 2023 06:42:40 -0700
From:   Yonghong Song <yhs@...a.com>
To:     baomingtong001@...suo.com, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
        mykolal@...com, shuah@...nel.org, jakub@...udflare.com,
        Jakub Kicinski <kuba@...nel.org>
Cc:     bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/bpf: Remove unneeded variable "ret"



On 6/13/23 1:50 AM, baomingtong001@...suo.com wrote:
> Fix the following coccicheck warning:
> 
> tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c:28:14-17: Unneeded 
> variable: "ret".
> 
> Return "1".
> 
> Signed-off-by: Mingtong Bao <baomingtong001@...suo.com>
> ---
>   tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c 
> b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c
> index 4a9f63bea66c..7f0146682577 100644
> --- a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c
> +++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf6.c
> @@ -25,10 +25,9 @@ static __noinline
>   int subprog_tail(struct __sk_buff *skb)
>   {
>       /* Don't propagate the constant to the caller */
> -    volatile int ret = 1;
> 
>       bpf_tail_call_static(skb, &jmp_table, 0);
> -    return ret;
> +    return 1;

Please pay attention to the comment:
    /* Don't propagate the constant to the caller */
which clearly says 'constant' is not preferred.

The patch introduced this change is:
     5e0b0a4c52d30   selftests/bpf: Test tail call counting with bpf2bpf 
and data on stack

The test intentionally want to:
   'Specifically when the size 

     of data allocated on BPF stack is not a multiple on 8.'

Note that with volatile and without volatile, the generated
code will be different and it will result in different
verification path.

cc Jakub for further clarification.

>   }
> 
>   SEC("tc")