RFC bpf: Add tracing multi link

hi,
this is another attempt to add batch attachment support for trampolines.

The patchset adds support to create 'multi' trampoline that is attached to set of functions represented by BTF IDs.

Previous post [0] tried to implement multi trampolines overlapping, but it turned out too complex, so I got back to simpler rules:
(we can discuss possible overlapping changes on top this change)

- multi trampoline can attach on top of existing single trampolines, which creates 2 types of function IDs:

1) single-IDs - functions that are attached within existing single trampolines
2) multi-IDs - functions that were 'not used' and are now taken by new 'multi' trampoline

- we allow overlapping of 2 'multi' trampolines if they are attached to same IDs
- we do now allow any other overlapping of 2 'multi' trampolines
- any new 'single' trampoline cannot attach to existing multi-IDs IDs

Maybe better explained on following example:

- you want to attach program P to functions A,B,C,D,E,F via bpf_trampoline_multi_attach

- D,E,F already have standard trampoline attached

- the bpf_trampoline_multi_attach will create new 'multi' trampoline which spans over A,B,C functions and attach program P to single trampolines D,E,F

- another program can be attached to A,B,C,D,E,F multi trampoline

- A,B,C functions are now 'not attachable' by any trampoline until the above 'multi' trampoline is released

- D,E,F functions are still attachable by any new trampoline

Also now that we have trampoline helpers for function arguments, we can just simply use function declaration with maximum arguments for any multi trampoline or related single trampoline.

There are couple of things missing in this post (that I know of), which I'll add when we agree that this is the way to go:

- attaching by functions names
- cookies support
- find out better way of locking trampolines in bpf_trampoline_multi_attach and bpf_trampoline_multi_detach
- bpf_tramp_update_set logic of calling multiple times register_ftrace_direct_multi function can be replaced by calling single update ftrace function that I have prototype for, but I will send it out separately to ftrace for review
- arm trampoline code changes (won't compile now)
- tests for error paths

thanks,
jirka

[0] - https://lore.kernel.org/bpf/[email protected]/
---
Jiri Olsa (17):
bpf: Link shimlink directly in trampoline
bpf: Replace bpf_tramp_links with bpf_tramp_progs
bpf: Store trampoline progs in arrays
bpf: Add multi tracing attach types
bpf: Add bpf_tramp_id object
bpf: Pass image struct to reg/unreg/modify fentry functions
bpf: Add support to postpone trampoline update
bpf: Factor bpf_trampoline_lookup function
bpf: Factor bpf_trampoline_put function
bpf: Add support to attach program to multiple trampolines
bpf: Add support to create tracing multi link
libbpf: Add btf__find_by_glob_kind function
libbpf: Add support to create tracing multi link selftests/bpf: Add fentry tracing multi func test selftests/bpf: Add fexit tracing multi func test selftests/bpf: Add fentry/fexit tracing multi func test selftests/bpf: Add mixed tracing multi func test

 arch/x86/net/bpf_jit_comp.c                                    |  38 ++---
 include/linux/bpf.h                                            |  98 ++++++++----
 include/linux/trace_events.h                                   |   5 +
 include/uapi/linux/bpf.h                                       |   7 +
 kernel/bpf/bpf_struct_ops.c                                    |  30 ++--
 kernel/bpf/syscall.c                                           |  56 +++++--
 kernel/bpf/trampoline.c                                        | 723 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--------------
 kernel/bpf/verifier.c                                          |   8 +-
 kernel/trace/bpf_trace.c                                       | 240 +++++++++++++++++++++++++++++
 net/bpf/bpf_dummy_struct_ops.c                                 |  16 +-
 net/bpf/test_run.c                                             |   2 +
 tools/include/uapi/linux/bpf.h                                 |   7 +
 tools/lib/bpf/bpf.c                                            |   7 +
 tools/lib/bpf/bpf.h                                            |   4 +
 tools/lib/bpf/btf.c                                            |  41 +++++
 tools/lib/bpf/btf.h                                            |   3 +
 tools/lib/bpf/libbpf.c                                         |  91 ++++++++++-
 tools/lib/bpf/libbpf.h                                         |  14 ++
 tools/lib/bpf/libbpf.map                                       |   1 +
 tools/lib/bpf/libbpf_internal.h                                |   1 +
 tools/testing/selftests/bpf/Makefile                           |   9 +-
 tools/testing/selftests/bpf/prog_tests/tracing_multi.c         | 158 ++++++++++++++++++++
 tools/testing/selftests/bpf/progs/tracing_multi_check.c        | 158 ++++++++++++++++++++
 tools/testing/selftests/bpf/progs/tracing_multi_fentry.c       |  17 +++
 tools/testing/selftests/bpf/progs/tracing_multi_fentry_fexit.c |  28 ++++
 tools/testing/selftests/bpf/progs/tracing_multi_fexit.c        |  20 +++
 tools/testing/selftests/bpf/progs/tracing_multi_mixed.c        |  43 ++++++
 27 files changed, 1624 insertions(+), 201 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/tracing_multi.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_check.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_fentry.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_fentry_fexit.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_fexit.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_mixed.c