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From: Alexei Starovoitov <ast@fb.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Alexei Starovoitov <ast@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>,
	Daniel Borkmann <daniel@iogearbox.net>,
	"x86@kernel.org" <x86@kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf-next 10/12] bpf: check types of arguments passed into helpers
Date: Sat, 12 Oct 2019 01:39:13 +0000
Message-ID: <ba51c8c3-94fc-413a-0935-aaa307127666@fb.com> (raw)
In-Reply-To: <CAEf4BzbmE_ADjjhu-+mLkQN_5HD6Azhrb-VuprAaoqxP1bb3OQ@mail.gmail.com>

On 10/11/19 12:02 PM, Andrii Nakryiko wrote:
> On Wed, Oct 9, 2019 at 9:15 PM Alexei Starovoitov <ast@kernel.org> wrote:
>>
>>   /* type of values returned from helper functions */
>> @@ -235,11 +236,17 @@ struct bpf_func_proto {
>>          bool gpl_only;
>>          bool pkt_access;
>>          enum bpf_return_type ret_type;
>> -       enum bpf_arg_type arg1_type;
>> -       enum bpf_arg_type arg2_type;
>> -       enum bpf_arg_type arg3_type;
>> -       enum bpf_arg_type arg4_type;
>> -       enum bpf_arg_type arg5_type;
>> +       union {
>> +               struct {
>> +                       enum bpf_arg_type arg1_type;
>> +                       enum bpf_arg_type arg2_type;
>> +                       enum bpf_arg_type arg3_type;
>> +                       enum bpf_arg_type arg4_type;
>> +                       enum bpf_arg_type arg5_type;
>> +               };
>> +               enum bpf_arg_type arg_type[5];
>> +       };
>> +       u32 *btf_id; /* BTF ids of arguments */
> 
> are you trying to save memory with this? otherwise not sure why it's
> not just `u32 btf_id[5]`? Even in that case it will save at most 12
> bytes (and I haven't even check alignment padding and stuff). So
> doesn't seem worth it?

Glad you asked :)
It cannot be "u32 btf_id[5];".
Guess why?
I think it's a cool trick.
I was happy when I finally figured out to solve it this way
after analyzing a bunch of ugly solutions.

>> + *
>> + *             The value to write, of *size*, is passed through eBPF stack and
>> + *             pointed by *data*.
> 
> typo? pointed __to__ by *data*?

I'm not an grammar expert. That was a copy paste from existing comment.

>> + *
>> + *             *ctx* is a pointer to in-kernel sutrct sk_buff.
>> + *
>> + *             This helper is similar to **bpf_perf_event_output**\ () but
>> + *             restricted to raw_tracepoint bpf programs.
> 
> nit: with BTF type tracking enabled?

sure.

>> +       for (i = 0; i < 5; i++) {
>> +               if (fn->arg_type[i] == ARG_PTR_TO_BTF_ID) {
>> +                       if (!fn->btf_id[i])
>> +                               fn->btf_id[i] = btf_resolve_helper_id(&env->log, fn->func, 0);
> 
> bug: 0 -> i  :)

Nice catch.
Clearly I don't have a use case yet for 2nd arg being ptr_to_btf.

  reply index

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-10  4:14 [PATCH v2 bpf-next 00/12] bpf: revolutionize bpf tracing Alexei Starovoitov
2019-10-10  4:14 ` [PATCH v2 bpf-next 01/12] bpf: add typecast to raw_tracepoints to help BTF generation Alexei Starovoitov
2019-10-10  4:14 ` [PATCH v2 bpf-next 02/12] bpf: add typecast to bpf helpers " Alexei Starovoitov
2019-10-10  4:14 ` [PATCH v2 bpf-next 03/12] bpf: process in-kernel BTF Alexei Starovoitov
2019-10-11 17:56   ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 04/12] bpf: add attach_btf_id attribute to program load Alexei Starovoitov
2019-10-11 17:58   ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 05/12] libbpf: auto-detect btf_id of raw_tracepoint Alexei Starovoitov
2019-10-11 18:02   ` Andrii Nakryiko
2019-10-11 18:07   ` Andrii Nakryiko
2019-10-12  0:40     ` Alexei Starovoitov
2019-10-12  1:29       ` Alexei Starovoitov
2019-10-12  4:38         ` Andrii Nakryiko
2019-10-12  4:53           ` Alexei Starovoitov
2019-10-12  4:39       ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 06/12] bpf: implement accurate raw_tp context access via BTF Alexei Starovoitov
2019-10-11 18:31   ` Andrii Nakryiko
2019-10-11 23:13     ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 07/12] bpf: attach raw_tp program with BTF via type name Alexei Starovoitov
2019-10-11 18:44   ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 08/12] bpf: add support for BTF pointers to interpreter Alexei Starovoitov
2019-10-10  4:15 ` [PATCH v2 bpf-next 09/12] bpf: add support for BTF pointers to x86 JIT Alexei Starovoitov
2019-10-11 18:48   ` Andrii Nakryiko
2019-10-10  4:15 ` [PATCH v2 bpf-next 10/12] bpf: check types of arguments passed into helpers Alexei Starovoitov
2019-10-11 19:02   ` Andrii Nakryiko
2019-10-12  1:39     ` Alexei Starovoitov [this message]
2019-10-12  4:25       ` Andrii Nakryiko
2019-10-10  4:15 ` [PATCH v2 bpf-next 11/12] bpf: disallow bpf_probe_read[_str] helpers Alexei Starovoitov
2019-10-11 19:03   ` Andrii Nakryiko
2019-10-10  4:15 ` [PATCH v2 bpf-next 12/12] selftests/bpf: add kfree_skb raw_tp test Alexei Starovoitov
2019-10-10 11:07   ` Ido Schimmel
2019-10-10 19:07     ` Alexei Starovoitov
2019-10-11 19:05   ` Andrii Nakryiko

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