On Thu, Jul 30, 2026 at 5:52 AM Mykyta Yatsenko
<[email protected]> wrote:
>
> From: Mykyta Yatsenko <[email protected]>
>
> 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, which are now file-local.
>
> Fixes: eadc0725ab8d3 ("tracing: Expose tracepoint BTF ids via tracefs")
> Reported-by: Mark Brown <[email protected]>
> Closes:
> https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Mykyta Yatsenko <[email protected]>
> ---
> include/trace/trace_events.h | 6 ++++--
> kernel/trace/trace_syscalls.c | 22 ++++++++++++++--------
> 2 files changed, 18 insertions(+), 10 deletions(-)
>
> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
> index 09ad57ac4b73..45ffbe04b580 100644
> --- a/include/trace/trace_events.h
> +++ b/include/trace/trace_events.h
> @@ -404,10 +404,12 @@ static inline notrace int
> trace_event_get_offsets_##call( \
> * [0] FUNC __bpf_trace_<call> (the BPF dispatcher)
> * [1] STRUCT trace_event_raw_<call> (the ring-buffer record)
> * Exposed via the events/<sys>/<name>/btf_ids tracefs file.
> + *
> + * File-local: the class name is not unique, so a global symbol would
> + * clash across translation units.
drop this comment? not super useful and file-local is default behavior
for BTF_ID_LIST anyways
> */
> #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)
>
This should go into Steven's tree, not bpf-next, right?
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 48ef1a93e576..9b5931f2f280 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -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"
> @@ -1305,13 +1306,18 @@ struct trace_event_functions exit_syscall_print_funcs
> = {
>
> #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.
> + * BTF id lists for the shared sys_enter/sys_exit dispatcher tracepoints,
> + * resolved by resolve_btfids. Defined locally rather than importing the
> + * DECLARE_EVENT_CLASS-generated lists, which are now file-local to the
> + * translation unit that instantiates the tracepoint.
drop "resolved by resolve_btfids", and drop the part about defined
locally because file-local, too much Claude style
> */
> -extern u32 __bpf_trace_btf_ids_sys_enter[];
> -extern u32 __bpf_trace_btf_ids_sys_exit[];
> +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 = {
> @@ -1321,7 +1327,7 @@ struct trace_event_class __refdata
> event_class_syscall_enter = {
> .get_fields = syscall_get_enter_fields,
> .raw_init = init_syscall_trace,
> #ifdef CONFIG_BPF_EVENTS
> - .btf_ids = __bpf_trace_btf_ids_sys_enter,
> + .btf_ids = syscall_enter_btf_ids,
> #endif
> };
>
> @@ -1336,7 +1342,7 @@ 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,
> + .btf_ids = syscall_exit_btf_ids,
> #endif
> };
>
>
> ---
> base-commit: eadc0725ab8d38c05148fce49f8d5c6a0e01f062
> change-id: 20260730-b4-fix_btf_tracefs-fdafda5fdb5b
>
> Best regards,
> --
> Mykyta Yatsenko <[email protected]>
>
