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

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Dec 22, 2023 at 09:55:09AM +0000, Alan Maguire wrote:
> 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.

would reading the /proc/kcore be an option? I'm under impression it's
default for distros but I might be wrong

jirka