netdev - Re: [PATCH v2 bpf-next 05/12] libbpf: auto-detect btf_id of raw

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Date:   Sat, 12 Oct 2019 04:53:16 +0000
From:   Alexei Starovoitov <ast@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        "x86@...nel.org" <x86@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 05/12] libbpf: auto-detect btf_id of
 raw_tracepoint

On 10/11/19 9:38 PM, Andrii Nakryiko wrote:
> On Fri, Oct 11, 2019 at 6:29 PM Alexei Starovoitov <ast@...com> wrote:
>>
>> On 10/11/19 5:40 PM, Alexei Starovoitov wrote:
>>>> But even if kernel supports attach_btf_id, I think users still need to
>>>> opt in into specifying attach_btf_id by libbpf. Think about existing
>>>> raw_tp programs that are using bpf_probe_read() because they were not
>>>> created with this kernel feature in mind. They will suddenly stop
>>>> working without any of user's fault.
>>>
>>> This one is excellent catch.
>>> loop1.c should have caught it, since it has
>>> SEC("raw_tracepoint/kfree_skb")
>>> {
>>>     int nested_loops(volatile struct pt_regs* ctx)
>>>      .. = PT_REGS_RC(ctx);
>>>
>>> and verifier would have rejected it.
>>> But the way the test is written it's not using libbpf's autodetect
>>> of program type, so everything is passing.
>>
>> With:
>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
>> b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
>> index 1c01ee2600a9..e27156dce10d 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
>> @@ -67,7 +67,7 @@ void test_bpf_verif_scale(void)
>>                    */
>>                   { "pyperf600_nounroll.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
>>
>> -               { "loop1.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
>> +               { "loop1.o", BPF_PROG_TYPE_UNSPEC},
>>                   { "loop2.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
>>
>> libbpf prog auto-detection kicks in and ...
>> # ./test_progs -n 3/10
>> libbpf: load bpf program failed: Permission denied
>> libbpf: -- BEGIN DUMP LOG ---
>> libbpf:
>> raw_tp 'kfree_skb' doesn't have 10-th argument
>> invalid bpf_context access off=80 size=8
>>
>> Good :) The verifier is doing its job.
> 
> oh, another super intuitive error from verifier ;) 10th argument, what?..

I know, but there is no env->linfo and no insn_idx to call
verbose_linfo() from there. That's even bigger refactoring
that I'd rather to later.