Re: [PATCH bpf-next v3 1/2] bpf: Do not include stack ptr register in precision backtracking bookkeeping

[Eduard Zingerman <eddyz87@gmail.com>]

Eduard Zingerman <eddyz87@gmail.com> writes:

> Yonghong Song <yonghong.song@linux.dev> writes:
>
> [...]
>
>> Let us say that we remove the code
>>
>> +    if (!src_reg) {
>> +        if (linked_regs)
>> +            return push_insn_history(env, state, 0, linked_regs);
>> +        return 0;
>> +    }
>>
>> The code should still work. But we might end up with more unnecessary
>> jump history entries. For example,
>>    dreg->type == PTR_TO_STACK, sreg is faked (i.e., BPF_SRC(insn->code) == BPF_K)
>>    and linked_regs = 0
>>
>> In this particular, we will still generate a jump table entry which
>> is not used in backtrack_insn().
>
> If linked_regs set is not empty the push_insn_history() is necessary
> even if src_reg is fake. Linked registers are handled at entry and at
> exit from backtrack_insn() outside of instruction pattern match if-else
> block.

Nah, you already handle this in the !src_reg check, sorry for the noise.
Thank you for explaining, makes sense.