Re: [PATCH v2 bpf-next 1/2] trace: bpf: Allow bpf to attach to bare tracepoints

[Yonghong Song]

On 1/16/21 10:21 AM, Qais Yousef wrote:
> Some subsystems only have bare tracepoints (a tracepoint with no
> associated trace event) to avoid the problem of trace events being an
> ABI that can't be changed.
>
>  From bpf presepective, bare tracepoints are what it calls
> RAW_TRACEPOINT().
>
> Since bpf assumed there's 1:1 mapping, it relied on hooking to
> DEFINE_EVENT() macro to create bpf mapping of the tracepoints. Since
> bare tracepoints use DECLARE_TRACE() to create the tracepoint, bpf had
> no knowledge about their existence.
>
> By teaching bpf_probe.h to parse DECLARE_TRACE() in a similar fashion to
> DEFINE_EVENT(), bpf can find and attach to the new raw tracepoints.
>
> Enabling that comes with the contract that changes to raw tracepoints
> don't constitute a regression if they break existing bpf programs.
> We need the ability to continue to morph and modify these raw
> tracepoints without worrying about any ABI.
>
> Update Documentation/bpf/bpf_design_QA.rst to document this contract.
>
> Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx>

Acked-by: Yonghong Song <yhs@xxxxxx>