From d5b201ed4feb7a11da242a97669424efeb724031 Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Thu, 30 Jul 2026 17:17:39 -0700 Subject: [PATCH] tracing: Make per-template BTF id lists file-local DECLARE_EVENT_CLASS emitted __bpf_trace_btf_ids_ through BTF_ID_LIST_GLOBAL, i.e. a global symbol named after the event class. The class name is not unique across the kernel, so the symbol multiply-defines whenever two translation units instantiate the same class. Switch to the file-local BTF_ID_LIST: the list is reached only through the event_class_.btf_ids pointer, initialised in the same unit, so tracefs readers never reference the symbol by name and resolve_btfids still fills the now-local .BTF_ids entries. The handcrafted syscall classes are the one cross-unit consumer: give them their own local BTF_ID_LIST rather than importing the generated sys_{enter,exit} lists. Link: https://patch.msgid.link/20260730-b4-fix_btf_tracefs-v2-1-6b66da8dc103@meta.com Fixes: eadc0725ab8d3 ("tracing: Expose tracepoint BTF ids via tracefs") Reported-by: Mark Brown Closes: https://lore.kernel.org/all/ff58b01c-3f5e-4d55-be82-609d2faaf12e@sirena.org.uk/ Signed-off-by: Mykyta Yatsenko Acked-by: Andrii Nakryiko Signed-off-by: Steven Rostedt --- include/trace/trace_events.h | 7 +++---- kernel/trace/trace_syscalls.c | 27 ++++++++++++++------------- 2 files changed, 17 insertions(+), 17 deletions(-) diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h index 09ad57ac4b73..93011f800d0f 100644 --- a/include/trace/trace_events.h +++ b/include/trace/trace_events.h @@ -398,7 +398,7 @@ static inline notrace int trace_event_get_offsets_##call( \ #define _TRACE_PERF_INIT(call) #endif /* CONFIG_PERF_EVENTS */ -#ifdef CONFIG_BPF_EVENTS +#if defined(CONFIG_BPF_EVENTS) && defined(CONFIG_DEBUG_INFO_BTF) /* * Per-template BTF id list, populated at link time by resolve_btfids: * [0] FUNC __bpf_trace_ (the BPF dispatcher) @@ -406,8 +406,7 @@ static inline notrace int trace_event_get_offsets_##call( \ * Exposed via the events///btf_ids tracefs file. */ #define _TRACE_BTF_IDS_DECLARE(call) \ - extern u32 __bpf_trace_btf_ids_##call[]; \ - BTF_ID_LIST_GLOBAL(__bpf_trace_btf_ids_##call, 2) \ + BTF_ID_LIST(__bpf_trace_btf_ids_##call) \ BTF_ID(func, __bpf_trace_##call) \ BTF_ID(struct, trace_event_raw_##call) @@ -417,7 +416,7 @@ static inline notrace int trace_event_get_offsets_##call( \ #else #define _TRACE_BTF_IDS_DECLARE(call) #define _TRACE_BTF_IDS_INIT(call) -#endif /* CONFIG_BPF_EVENTS */ +#endif /* CONFIG_BPF_EVENTS && CONFIG_DEBUG_INFO_BTF */ #include "stages/stage6_event_callback.h" diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c index 48ef1a93e576..e35744049e3f 100644 --- a/kernel/trace/trace_syscalls.c +++ b/kernel/trace/trace_syscalls.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include "trace_output.h" @@ -1303,15 +1304,15 @@ struct trace_event_functions exit_syscall_print_funcs = { .trace = print_syscall_exit, }; -#ifdef CONFIG_BPF_EVENTS -/* - * BTF id lists generated by DECLARE_EVENT_CLASS for the sys_enter and - * sys_exit tracepoints. The auto-generated event_class_sys_{enter,exit} - * is unused (per-syscall events share the handcrafted classes below), - * but the id lists themselves are global and reusable. - */ -extern u32 __bpf_trace_btf_ids_sys_enter[]; -extern u32 __bpf_trace_btf_ids_sys_exit[]; +#if defined(CONFIG_BPF_EVENTS) && defined(CONFIG_DEBUG_INFO_BTF) +/* BTF id lists for the shared sys_enter/sys_exit dispatcher tracepoints. */ +BTF_ID_LIST(syscall_enter_btf_ids) +BTF_ID(func, __bpf_trace_sys_enter) +BTF_ID(struct, trace_event_raw_sys_enter) + +BTF_ID_LIST(syscall_exit_btf_ids) +BTF_ID(func, __bpf_trace_sys_exit) +BTF_ID(struct, trace_event_raw_sys_exit) #endif struct trace_event_class __refdata event_class_syscall_enter = { @@ -1320,8 +1321,8 @@ struct trace_event_class __refdata event_class_syscall_enter = { .fields_array = syscall_enter_fields_array, .get_fields = syscall_get_enter_fields, .raw_init = init_syscall_trace, -#ifdef CONFIG_BPF_EVENTS - .btf_ids = __bpf_trace_btf_ids_sys_enter, +#if defined(CONFIG_BPF_EVENTS) && defined(CONFIG_DEBUG_INFO_BTF) + .btf_ids = syscall_enter_btf_ids, #endif }; @@ -1335,8 +1336,8 @@ struct trace_event_class __refdata event_class_syscall_exit = { }, .fields = LIST_HEAD_INIT(event_class_syscall_exit.fields), .raw_init = init_syscall_trace, -#ifdef CONFIG_BPF_EVENTS - .btf_ids = __bpf_trace_btf_ids_sys_exit, +#if defined(CONFIG_BPF_EVENTS) && defined(CONFIG_DEBUG_INFO_BTF) + .btf_ids = syscall_exit_btf_ids, #endif };