On Thu, Feb 05, 2026 at 05:16:49PM +0800, Menglong Dong wrote:
> On 2026/2/3 17:38 Jiri Olsa <[email protected]> write:
> > Adding bpf_trampoline_multi_attach/detach functions that allows
> > to attach/detach multi tracing trampoline.
> >
> > The attachment is defined with bpf_program and array of BTF ids
> > of functions to attach the bpf program to.
> >
> [...]
> > @@ -367,7 +367,11 @@ static struct bpf_trampoline
> > *bpf_trampoline_lookup(u64 key, unsigned long ip)
> > head = &trampoline_ip_table[hash_64(tr->ip, TRAMPOLINE_HASH_BITS)];
> > hlist_add_head(&tr->hlist_ip, head);
> > refcount_set(&tr->refcnt, 1);
> > +#ifdef CONFIG_LOCKDEP
> > + mutex_init_with_key(&tr->mutex, &__lockdep_no_track__);
> > +#else
> > mutex_init(&tr->mutex);
> > +#endif
> > for (i = 0; i < BPF_TRAMP_MAX; i++)
> > INIT_HLIST_HEAD(&tr->progs_hlist[i]);
> > out:
> > @@ -1400,6 +1404,188 @@ int __weak arch_bpf_trampoline_size(const struct
> > btf_func_model *m, u32 flags,
> > return -ENOTSUPP;
> > }
> >
> > +#if defined(CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS) &&
> > defined(CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS)
>
> Hi, Jiri. It's great to see your tracing_multi link finally. It looks great ;)
heya, thanks ;-)
>
> After analyzing a little deeper on the SINGLE_FTRACE_DIRECT_OPS, I
> understand why it is only supported on x86_64 for now. It seems that
> it's a little hard to implement it in the other arch, as we need to
> restructure the implement of ftrace direct call.
>
> So do we need some more ftrace API here to make the tracing multi-link
> independent from SINGLE_FTRACE_DIRECT_OPS? Otherwise, we can only
> use it on x86_64.
I tried to describe it in commit [2] changelog:
At the moment we can enable this only on x86 arch, because arm relies
on ftrace_ops object representing just single trampoline image (stored
in ftrace_ops::direct_call). Archs that do not support this will continue
to use *_ftrace_direct api.
>
> Have you ever tried to implement the SINGLE_FTRACE_DIRECT_OPS on arm64?
> The direct call on arm64 is so complex, and I didn't work it out :/
yes, it seems to be difficult atm, Mark commented on that in [1],
I don't know arm that good to be of much help in here, cc-ing Mark
jirka
[1] https://lore.kernel.org/bpf/aIyNOd18TRLu8EpY@J2N7QTR9R3/
[2] 424f6a361096 ("bpf,x86: Use single ftrace_ops for direct calls")
>
> Thanks!
> Menglong Dong
>
> > +
> > +struct fentry_multi_data {
> > + struct ftrace_hash *unreg;
> > + struct ftrace_hash *modify;
> > + struct ftrace_hash *reg;
> > +};
> > +
> [...]
> >
> >
> >
>
>
>
>
