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Subject: Re: [PATCH v1] selftests:bpf:Fix repeated initialization
To:     Wang Ming <machel@vivo.com>, Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
        bpf@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     opensource.kernel@vivo.com
References: <20230705123432.1655-1-machel@vivo.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <cfc5f09e-7af1-abb9-aee9-737e3fe09c77@iogearbox.net>
Date:   Wed, 5 Jul 2023 15:32:08 +0200
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On 7/5/23 2:33 PM, Wang Ming wrote:
> In use_missing_map function, value is
> initialized twice.There is no
> connection between the two assignment.
> This patch could fix this bug.

Please never submit patches where you are just speculating and did not even
bother to run BPF selftests !

Otherwise you would have seen that your change is breaking it :

Error: #126 log_fixup
Error: #126/5 log_fixup/missing_map
   Error: #126/5 log_fixup/missing_map
   missing_map:PASS:skel_open 0 nsec
   libbpf: prog 'use_missing_map': BPF program load failed: Invalid argument
   libbpf: prog 'use_missing_map': failed to load: -22
   libbpf: failed to load object 'test_log_fixup'
   libbpf: failed to load BPF skeleton 'test_log_fixup': -22
   missing_map:PASS:load_fail 0 nsec
   missing_map:PASS:existing_map_autocreate 0 nsec
   missing_map:PASS:missing_map_autocreate 0 nsec
   missing_map:FAIL:log_buf unexpected log_buf: '8: <invalid BPF map reference>
   BPF map 'missing_map' is referenced but wasn't created
   ' is not a substring of 'reg type unsupported for arg#0 function use_missing_map#20
   0: R1=ctx(off=0,imm=0) R10=fp0
   ; int use_missing_map(const void *ctx)
   0: (b4) w1 = 0                        ; R1_w=0
   ; int zero = 0;
   1: (63) *(u32 *)(r10 -4) = r1         ; R1_w=0 R10=fp0 fp-8=0000????
   2: (bf) r2 = r10                      ; R2_w=fp0 R10=fp0
   ;
   3: (07) r2 += -4                      ; R2_w=fp-4
   ; return bpf_map_lookup_elem(&missing_map, &zero) != NULL;
   4: <invalid BPF map reference>
   BPF map 'missing_map' is referenced but wasn't created
   processed 5 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0

> Signed-off-by: Wang Ming <machel@vivo.com>
> ---
>   tools/testing/selftests/bpf/progs/test_log_fixup.c | 8 ++------
>   1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/test_log_fixup.c b/tools/testing/selftests/bpf/progs/test_log_fixup.c
> index 1bd48feaaa42..1c49b2f9be6c 100644
> --- a/tools/testing/selftests/bpf/progs/test_log_fixup.c
> +++ b/tools/testing/selftests/bpf/progs/test_log_fixup.c
> @@ -52,13 +52,9 @@ struct {
>   SEC("?raw_tp/sys_enter")
>   int use_missing_map(const void *ctx)
>   {
> -	int zero = 0, *value;
> +	int zero = 0;
>   
> -	value = bpf_map_lookup_elem(&existing_map, &zero);
> -
> -	value = bpf_map_lookup_elem(&missing_map, &zero);
> -
> -	return value != NULL;
> +	return bpf_map_lookup_elem(&missing_map, &zero) != NULL;
>   }
>   
>   extern int bpf_nonexistent_kfunc(void) __ksym __weak;
>