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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@arm.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20210119122237.2426878-2-qais.yousef@arm.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.