Re: [PATCH v2 bpf-next] selftests/bpf: fix "alu with different scalars 1" on s390

[Daniel Borkmann <daniel@iogearbox.net>]

On 7/16/19 12:13 AM, Alexei Starovoitov wrote:
> On Thu, Jul 4, 2019 at 1:53 AM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>>
>> BPF_LDX_MEM is used to load the least significant byte of the retrieved
>> test_val.index, however, on big-endian machines it ends up retrieving
>> the most significant byte.
>>
>> Use the correct least significant byte offset on big-endian machines.
>>
>> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
>> ---
>>
>> v1->v2:
>> - use __BYTE_ORDER instead of __BYTE_ORDER__.
>>
>>  tools/testing/selftests/bpf/verifier/value_ptr_arith.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/tools/testing/selftests/bpf/verifier/value_ptr_arith.c b/tools/testing/selftests/bpf/verifier/value_ptr_arith.c
>> index c3de1a2c9dc5..e5940c4e8b8f 100644
>> --- a/tools/testing/selftests/bpf/verifier/value_ptr_arith.c
>> +++ b/tools/testing/selftests/bpf/verifier/value_ptr_arith.c
>> @@ -183,7 +183,11 @@
>>         BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
>>         BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
>>         BPF_EXIT_INSN(),
>> +#if __BYTE_ORDER == __LITTLE_ENDIAN
>>         BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),
>> +#else
>> +       BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, sizeof(int) - 1),
>> +#endif
> 
> I think tests should be arch and endian independent where possible.
> In this case test_val.index is 4 byte and 4 byte load should work just as well.

Yes, agree, this should be fixed with BPF_W as load.

Thanks,
Daniel