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Date: Sat, 16 Jan 2021 18:03:37 -0800 From: Yonghong Song <yhs@...com> To: Qais Yousef <qais.yousef@....com>, <netdev@...r.kernel.org>, <bpf@...r.kernel.org> CC: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Steven Rostedt <rostedt@...dmis.org>, "Peter Zijlstra (Intel)" <peterz@...radead.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 bpf-next 1/2] trace: bpf: Allow bpf to attach to bare tracepoints 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@....com> Acked-by: Yonghong Song <yhs@...com>
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