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Fri, 15 May 2026 09:41:34 -0700 (PDT) Received: from localhost ([2a03:2880:30ff:1::]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45da15a6454sm15745826f8f.34.2026.05.15.09.41.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 May 2026 09:41:34 -0700 (PDT) From: Mykyta Yatsenko Subject: [PATCH bpf-next 0/3] tracing: Expose tracepoint BTF ids via tracefs Date: Fri, 15 May 2026 09:41:00 -0700 Message-Id: <20260515-generic_tracepoint-v1-0-aa619fa94132@meta.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-B4-Tracking: v=1; b=H4sIAJ1MB2oC/x3MQQqDMBAF0KsMf20gSq0hVymlxDjqbMYwCUUQ7 17oO8C7UNmEKyJdMP5KlUMRqe8IeU+6sZMFkTD44elHH9zGyib50yxlLodoc8sjhDSmKc19QEc oxquc//SFuaxO+Wx43/cPxrtSIm4AAAA= X-Change-ID: 20260508-generic_tracepoint-d488a5a7ab18 To: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, kafai@meta.com, kernel-team@meta.com, eddyz87@gmail.com, memxor@gmail.com, peterz@infradead.org, rostedt@goodmis.org Cc: Mykyta Yatsenko X-Mailer: b4 0.16-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1778863293; l=3677; i=yatsenko@meta.com; s=20260324; h=from:subject:message-id; bh=3hNAaiR4ZlfYXtpbG/PId2FkplkENPT7MqXDDOBnFn4=; b=BBzsVsC/zpQAmiqIbkn4dThyRxbKUTu50Vc6CuwvXJTr8mQ9c+6jIpoo16kerIWDws86OwJHT 0g+D9lItgN5Cq5EnygGLNawL2KbFQ4Qcbj76ofALA0u9baW+FawQRtc X-Developer-Key: i=yatsenko@meta.com; a=ed25519; pk=1zCUBXUa66KmzfjNsG8YNlMj2ckPdqBPvFq2ww3/YaA= BPF and other consumers that want to attach to or decode a generic tracepoint need three pieces of BTF information for it: - the BTF of the object that owns the tracepoint's types - the FUNC_PROTO describing the tracepoint arguments (with names), consumed by raw_tp / tp_btf BPF programs - the STRUCT id of trace_event_raw_, the ring-buffer record consumed by classic BPF_PROG_TYPE_TRACEPOINT programs Today none of this is easily discoverable from userspace. The kernel knows the ids - resolve_btfids fills them in at link time - but consumers have to search them by the naming convention ("__bpf_trace_", "trace_event_raw_"), walking BTF for every tracepoint. This series stores those ids in trace_event_class and exposes them via events///btf_ids, e.g. # cat /sys/kernel/tracing/events/sched/sched_switch/btf_ids btf_obj_id: 1 raw_btf_id: 28882 tp_btf_id: 106335 # bpftool btf dump id 1 root_id 28882 format raw [28882] FUNC_PROTO '(anon)' ret_type_id=0 vlen=5 '__data' type_id=9 'preempt' type_id=60674 'prev' type_id=219 'next' type_id=219 'prev_state' type_id=108689 # bpftool btf dump id 1 root_id 106335 format raw [106335] STRUCT 'trace_event_raw_sched_switch' size=64 vlen=9 'ent' type_id=104654 bits_offset=0 'prev_comm' type_id=580 bits_offset=64 'prev_pid' type_id=92875 bits_offset=192 'prev_prio' type_id=79365 bits_offset=224 'prev_state' type_id=83958 bits_offset=256 'next_comm' type_id=580 bits_offset=320 'next_pid' type_id=92875 bits_offset=448 'next_prio' type_id=79365 bits_offset=480 '__data' type_id=407 bits_offset=512 For per-syscall events (all sharing the same dispatcher), raw_btf_id is 0 — raw_tp / tp_btf programs attach to raw_syscalls/sys_{enter,exit}, not per-syscall events: # cat /sys/kernel/tracing/events/syscalls/sys_enter_write/btf_ids btf_obj_id: 1 raw_btf_id: 0 tp_btf_id: 106540 This unlocks few usecases for consumers: - Resolving tp_btf attach targets and argument types directly, instead of constructing "__bpf_trace_*" names and re-discovering them in vmlinux BTF. - Get a stable, machine-readable contract for tracepoint payloads, with field names preserved. Patch 1 exports the two BTF helpers the tracing core needs. Patch 2 wires DECLARE_EVENT_CLASS to publish the ids, adds the tracefs reader, and wires the syscall classes so per-syscall events carry tp_btf_id (raw_btf_id is 0 there — see above). Patch 3 adds a selftest covering the sched_switch tracepoint. Signed-off-by: Mykyta Yatsenko --- Mykyta Yatsenko (3): bpf: Export btf_get_module_btf() and btf_relocate_id() tracing: Expose tracepoint BTF ids via tracefs selftests/bpf: Add test for tracepoint btf_ids tracefs file include/linux/btf.h | 2 + include/linux/trace_events.h | 9 ++ include/trace/trace_events.h | 24 ++++ kernel/bpf/btf.c | 6 +- kernel/trace/trace_events.c | 81 +++++++++++++- kernel/trace/trace_syscalls.c | 17 +++ .../testing/selftests/bpf/prog_tests/tp_btf_ids.c | 124 +++++++++++++++++++++ 7 files changed, 260 insertions(+), 3 deletions(-) --- base-commit: 3fe213c040b3a175f6051ed3aaf823a430ac0b08 change-id: 20260508-generic_tracepoint-d488a5a7ab18 Best regards, -- Mykyta Yatsenko