Re: [PATCH v2] tracing: Make per-template BTF id lists file-local

On Thu, Jul 30, 2026 at 5:18=E2=80=AFPM 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.
>
> Fixes: eadc0725ab8d3 ("tracing: Expose tracepoint BTF ids via tracefs")
> Reported-by: Mark Brown <[email protected]>
> Closes: https://lore.kernel.org/all/ff58b01c-3f5e-4d55-be82-609d2faaf12e@=
sirena.org.uk/
> Signed-off-by: Mykyta Yatsenko <[email protected]>
> ---
> Changes in v2:
> - Emit the per-class BTF id list only under CONFIG_DEBUG_INFO_BTF;
>   without BTF the ids are unresolved and BTF_ID_LIST falls back to a
>   128-entry (512-byte) per-class stub, adding hundreds of KB of BSS
>   across the ~1000 event classes (reported in review of v1).
> - Link to v1: https://patch.msgid.link/20260730-b4-fix_btf_tracefs-v1-1-5=
[email protected]
> ---
> Changes in v2:
> - Emit the per-class BTF id list only under CONFIG_DEBUG_INFO_BTF;
> without BTF the ids are unresolved and BTF_ID_LIST falls back to a
> 128-entry stub.
> - Remove verbose comments (Andrii)
> - Link to v1: https://patch.msgid.link/20260730-b4-fix_btf_tracefs-v1-1-5=
[email protected]
> ---
>  include/trace/trace_events.h  |  7 +++----
>  kernel/trace/trace_syscalls.c | 27 ++++++++++++++-------------
>  2 files changed, 17 insertions(+), 17 deletions(-)
>

LGTM

Acked-by: Andrii Nakryiko <[email protected]>


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