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Libbpf supports single virtual __kconfig extern currently: LINUX_KERNEL_VERSION. LINUX_KERNEL_VERSION isn't coming from /proc/kconfig.gz and is intead customly filled out by libbpf. This patch generalizes this approach to support more such virtual __kconfig externs. One such extern added in this patch is LINUX_HAS_BPF_COOKIE which is used for BPF-side USDT supporting code in usdt.bpf.h instead of using CO-RE-based enum detection approach for detecting bpf_get_attach_cookie() BPF helper. This allows to remove otherwise not needed CO-RE dependency and keeps user-space and BPF-side parts of libbpf's USDT support strictly in sync in terms of their feature detection. We'll use similar approach for syscall wrapper detection for BPF_KSYSCALL() BPF-side macro in follow up patch. Generally, currently libbpf reserves CONFIG_ prefix for Kconfig values and LINUX_ for virtual libbpf-backed externs. In the future we might extend the set of prefixes that are supported. This can be done without any breaking changes, as currently any __kconfig extern with unrecognized name is rejected. For LINUX_xxx externs we support the normal "weak rule": if libbpf doesn't recognize given LINUX_xxx extern but such extern is marked as __weak, it is not rejected and defaults to zero. This follows CONFIG_xxx handling logic and will allow BPF applications to opportunistically use newer libbpf virtual externs without breaking on older libbpf versions unnecessarily. Tested-by: Alan Maguire <alan.maguire@oracle.com> Reviewed-by: Alan Maguire <alan.maguire@oracle.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/r/20220714070755.3235561-2-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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.