Re: [PATCH v1] selftests:bpf:Fix repeated initialization

[Daniel Borkmann]

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@xxxxxxxx>
> ---
>   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;