On Mon, Feb 24, 2025 at 11:35 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> On Tue, Feb 25, 2025 at 1:30 AM Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> >
> > On Mon, Feb 24, 2025 at 3:46 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> > >
> > > + } else if (prog->expected_attach_type == BPF_TRACE_FEXIT &&
> > > + btf_id_set_contains(&fexit_deny, btf_id)) {
> > > + verbose(env, "Attaching fexit to __noreturn functions is rejected.\n");
> > > + return -EINVAL;
> >
> > Just realized that this needs to include
> > prog->expected_attach_type == BPF_MODIFY_RETURN
> > since it's doing __bpf_tramp_enter() too.
>
> I will add it.
>
> >
> > Also the list must only contain existing functions.
> > Otherwise there are plenty of build warns:
> > BTFIDS vmlinux
> > WARN: resolve_btfids: unresolved symbol xen_start_kernel
> > WARN: resolve_btfids: unresolved symbol xen_cpu_bringup_again
> > WARN: resolve_btfids: unresolved symbol usercopy_abort
> > WARN: resolve_btfids: unresolved symbol snp_abort
> > WARN: resolve_btfids: unresolved symbol sev_es_terminate
> > WARN: resolve_btfids: unresolved symbol rust_helper_BUG
> > ...
>
> I missed these warnings.
> It looks like we need to add "#ifdef XXXX" to each function.
> Alternatively, could we just compare the function name with
> prog->aux->attach_func_name instead?
Strings are much less efficient than btf_ids.
Especially comparing across many strings.
To minimize ifdef-s lets remove all functions that bpf cannot
attach anyway (that are not in available_filter_functions).
Then drop all that call panic/BUG equivalent,
since refcnt on trampoline is irrelevant at that point.
That will remove even more functions.
At the end the list will be short with few ifdef-s.
This is a temporary workaround anyway, so let's not get too creative.
