arch: arm: bpf: Converting cBPF to eBPF for arm 32 bit

[Shubham Bansal]

Okay. My mistake. I just checked the verify function.

Apologies.
Best,
Shubham Bansal


On Sun, May 7, 2017 at 1:57 AM, Shubham Bansal
<illusionist.neo at gmail.com> wrote:
> Thanks David.
>
> Hi all,
>
> I have two questions about the code at arch/arm64/net/bpf_jit_comp.c.
>
> 1. At line 708, " const u8 r1 = bpf2a64[BPF_REG_1]; /* r1: struct
> sk_buff *skb */ ".
>     Why is this code using BPF_REG_1 before saving it? As far as I
> know, BPF_REG_1 has pointer to bpf program context and this code
> clearly is overwriting that pointer which makes that pointer useless
> for future usage. It clearly looks like a bug.
>
> 2. At line 256, " emit(A64_LDR64(prg, tmp, r3), ctx); ".
>     This line of code is used to load an array( of pointers ) element,
> where r3 is used as an index of that array. Shouldn't it be be
> arithmetic left shifted by 3 or multiplied by 8 to get the right
> address in that array of pointers ?
>
> Apologies if any of the above question is stupid to ask.
>
> Best,
> Shubham
> Best,
> Shubham Bansal
>
>
> On Sun, May 7, 2017 at 12:08 AM, David Miller <davem at davemloft.net> wrote:
>> From: Shubham Bansal <illusionist.neo at gmail.com>
>> Date: Sat, 6 May 2017 22:18:16 +0530
>>
>>> Hi Daniel,
>>>
>>> Thanks for the last reply about the testing of eBPF JIT.
>>>
>>> I have one issue though, I am not able to find what BPF_ABS and
>>> BPF_IND instruction does exactly.
>>
>> They are not instructions, they are modifiers for the BPF_LD
>> instruction which indicate an SKB load is to be performed.
>>
>> You never need to ask what a BPF instruction does, it is clear
>> defined in the BPF interperter found in kernel/bpf/core.c
>>
>> Look for the case statement LD_ABS_W and friends in __bpf_prog_run().