Re: [PATCH dwarves] pahole: Inject kfunc decl tags into BTF

[Alan Maguire <alan.maguire@oracle.com>]

On 21/12/2023 18:07, Alexei Starovoitov wrote:
> On Thu, Dec 21, 2023 at 9:43 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>
>> On 21/12/2023 17:05, Alexei Starovoitov wrote:
>>> On Thu, Dec 21, 2023 at 12:35 AM Jiri Olsa <olsajiri@gmail.com> wrote:
>>>> you need to pick up only 'BTF_ID(func, ...)' IDs that belongs to SET8 lists,
>>>> which are bounded by __BTF_ID__set8__<name> symbols, which also provide size
>>>
>>> +1
>>>
>>>>>
>>>>> Maybe we need a codemod from:
>>>>>
>>>>>         BTF_ID(func, ...
>>>>>
>>>>> to:
>>>>>
>>>>>         BTF_ID(kfunc, ...
>>>>
>>>> I think it's better to keep just 'func' and not to do anything special for
>>>> kfuncs in resolve_btfids logic to keep it simple
>>>>
>>>> also it's going to be already in pahole so if we want to make a fix in future
>>>> you need to change pahole, resolve_btfids and possibly also kernel
>>>
>>> I still don't understand why you guys want to add it to vmlinux BTF.
>>> The kernel has no use in this additional data.
>>> It already knows about all kfuncs.
>>> This extra memory is a waste of space from kernel pov.
>>> Unless I am missing something.
>>>
>>> imo this logic belongs in bpftool only.
>>> It can dump vmlinux BTF and emit __ksym protos into vmlinux.h
>>>
>>
>> If the goal is to have bpftool detect all kfuncs, would having a BPF
>> kfunc iterator that bpftool could use to iterate over registered kfuncs
>> work perhaps?
> 
> The kernel code ? Why ?
> bpftool can do the same thing as this patch. Iterate over set8 in vmlinux elf.

Most distros don't have the vmlinux binary easily available; it needs to
be either downloaded as part of debuginfo packages or uncompressed from
vmlinuz.