Re: [RFC bpf-next 04/12] bpf: Add struct bpf_tramp_node object

On Tue, Feb 3, 2026 at 1:39 AM Jiri Olsa [off-list ref] wrote:

Adding struct bpf_tramp_node to decouple the link out of the trampoline
attachment info.

At the moment the object for attaching bpf program to the trampoline is
'struct bpf_tramp_link':

  struct bpf_tramp_link {
       struct bpf_link link;
       struct hlist_node tramp_hlist;
       u64 cookie;
  }

The link holds the bpf_prog pointer and forces one link - one program
binding logic. In following changes we want to attach program to multiple
trampolines but have just one bpf_link object.

Splitting struct bpf_tramp_link into:

  struct bpf_tramp_link {
       struct bpf_link link;
       struct bpf_tramp_node node;
  };

  struct bpf_tramp_node {
       struct hlist_node tramp_hlist;
       struct bpf_prog *prog;
       u64 cookie;
  };

I'm a bit confused here. For singular fentry/fexit attachment we have
one trampoline and one program, right? For multi-fentry, we have
multiple trampoline, but still one program pointer, no? So why put a
prog pointer into tramp_node?.. You do want cookie in tramp_node, yes,
but not the program. Because then there is also a question what is
bpf_link's prog pointing to?...

where 'struct bpf_tramp_link' defines standard single trampoline link,
and 'struct bpf_tramp_node' is the attachment trampoline object. This
will allow us to define link for multiple trampolines, like:

  struct bpf_tracing_multi_link {
       struct bpf_link link;
       ...
       int nodes_cnt;
       struct bpf_tracing_multi_node nodes[] __counted_by(nodes_cnt);
  };

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/arm64/net/bpf_jit_comp.c  |  58 +++++++++----------
 arch/s390/net/bpf_jit_comp.c   |  42 +++++++-------
 arch/x86/net/bpf_jit_comp.c    |  54 ++++++++---------
 include/linux/bpf.h            |  47 ++++++++-------
 kernel/bpf/bpf_struct_ops.c    |  24 ++++----
 kernel/bpf/syscall.c           |  25 ++++----
 kernel/bpf/trampoline.c        | 102 ++++++++++++++++-----------------
 net/bpf/bpf_dummy_struct_ops.c |  11 ++--
 8 files changed, 185 insertions(+), 178 deletions(-)

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