Re: [PATCH bpf-next v2 1/6] bpf: Introduce 64-bit bitops kfuncs

[Leon Hwang <leon.hwang@linux.dev>]

On 2026/2/20 01:50, Alexei Starovoitov wrote:
> On Thu, Feb 19, 2026 at 6:30 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>>
>>
>> +static bool bpf_kfunc_is_fastcall(struct bpf_verifier_env *env, u32 func_id, u32 flags)
>> +{
>> +       if (!(flags & KF_FASTCALL))
>> +               return false;
>> +
>> +       if (!env->prog->jit_requested)
>> +               return true;
>> +
>> +       if (func_id == special_kfunc_list[KF_bpf_clz64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_clz64);
>> +       if (func_id == special_kfunc_list[KF_bpf_ctz64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_ctz64);
>> +       if (func_id == special_kfunc_list[KF_bpf_ffs64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_ffs64);
>> +       if (func_id == special_kfunc_list[KF_bpf_fls64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_fls64);
>> +       if (func_id == special_kfunc_list[KF_bpf_bitrev64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_bitrev64);
>> +       if (func_id == special_kfunc_list[KF_bpf_popcnt64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_popcnt64);
>> +       if (func_id == special_kfunc_list[KF_bpf_rol64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_rol64);
>> +       if (func_id == special_kfunc_list[KF_bpf_ror64])
>> +               return bpf_jit_inlines_kfunc_call(bpf_ror64);
> 
> This is too ugly. Find a way to do it differently.

Agreed.

I'd like to introduce a new flag KF_JIT_MAY_INLINE to indicate the kfunc
will be inlined by JIT backends if possible. As for those kfuncs w/
KF_FASTCALL w/o KF_JIT_MAY_INLINE, they are fastcall always.

Thanks,
Leon