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tracing: Make per-template BTF id lists file-local

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DECLARE_EVENT_CLASS emitted __bpf_trace_btf_ids_<call> 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_<call>.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: eadc0725ab ("tracing: Expose tracepoint BTF ids via tracefs")
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/all/ff58b01c-3f5e-4d55-be82-609d2faaf12e@sirena.org.uk/
Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Mykyta Yatsenko
2026-07-30 17:17:39 -07:00
committed by Steven Rostedt
parent efdcfd9b4f
commit d5b201ed4f
2 changed files with 17 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
include/trace/trace_events.h
View File

@@ -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_<call> (the BPF dispatcher)
@@ -406,8 +406,7 @@ static inline notrace int trace_event_get_offsets_##call( \
* Exposed via the events/<sys>/<name>/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"

27
kernel/trace/trace_syscalls.c
View File

@@ -9,6 +9,7 @@
#include <linux/ftrace.h>
#include <linux/perf_event.h>
#include <linux/xarray.h>
#include <linux/btf_ids.h>
#include <asm/syscall.h>
#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
};