linux-kernel - Re: [PATCH bpf-next v2] bpf: remove set but not used variable 'dst

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Message-ID: <C7067847-8EDB-49B5-8DDF-C8504BB82962@fb.com>
Date:   Sat, 18 Apr 2020 06:13:48 +0000
From:   Song Liu <songliubraving@...com>
To:     Mao Wenan <maowenan@...wei.com>
CC:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Martin Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "kpsingh@...omium.org" <kpsingh@...omium.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2] bpf: remove set but not used variable
 'dst_known'



> On Apr 17, 2020, at 6:37 PM, Mao Wenan <maowenan@...wei.com> wrote:
> 
> Fixes gcc '-Wunused-but-set-variable' warning:
> 
> kernel/bpf/verifier.c:5603:18: warning: variable ‘dst_known’
> set but not used [-Wunused-but-set-variable], delete this
> variable.
> 
> Signed-off-by: Mao Wenan <maowenan@...wei.com>

Acked-by: Song Liu <songliubraving@...com>

With one nit below. 

> ---
> v2: remove fixes tag in commit log. 
> kernel/bpf/verifier.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 04c6630cc18f..c9f50969a689 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5600,7 +5600,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
> {
> 	struct bpf_reg_state *regs = cur_regs(env);
> 	u8 opcode = BPF_OP(insn->code);
> -	bool src_known, dst_known;
> +	bool src_known;

This is not a hard rule, but we prefer to keep variable definition in 
"reverse Christmas tree" order. Since we are on this function, let's 
reorder these definitions to something like:

        u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
        struct bpf_reg_state *regs = cur_regs(env);
        u8 opcode = BPF_OP(insn->code);
        u32 dst = insn->dst_reg;
        s64 smin_val, smax_val;
        u64 umin_val, umax_val;
        bool src_known;
        int ret;