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Andrii Nakryiko says:
====================
Add SEC("ksyscall")/SEC("kretsyscall") sections and corresponding
bpf_program__attach_ksyscall() API that simplifies tracing kernel syscalls
through kprobe mechanism. Kprobing syscalls isn't trivial due to varying
syscall handler names in the kernel and various ways syscall argument are
passed, depending on kernel architecture and configuration. SEC("ksyscall")
allows user to not care about such details and just get access to syscall
input arguments, while libbpf takes care of necessary feature detection logic.
There are still more quirks that are not straightforward to hide completely
(see comments about mmap(), clone() and compat syscalls), so in such more
advanced scenarios user might need to fall back to plain SEC("kprobe")
approach, but for absolute majority of users SEC("ksyscall") is a big
improvement.
As part of this patch set libbpf adds two more virtual __kconfig externs, in
addition to existing LINUX_KERNEL_VERSION: LINUX_HAS_BPF_COOKIE and
LINUX_HAS_SYSCALL_WRAPPER, which let's libbpf-provided BPF-side code minimize
external dependencies and assumptions and let's user-space part of libbpf to
perform all the feature detection logic. This benefits USDT support code,
which now doesn't depend on BPF CO-RE for its functionality.
v1->v2:
- normalize extern variable-related warn and debug message formats (Alan);
rfc->v1:
- drop dependency on kallsyms and speed up SYSCALL_WRAPPER detection (Alexei);
- drop dependency on /proc/config.gz in bpf_tracing.h (Yaniv);
- add doc comment and ephasize mmap(), clone() and compat quirks that are
not supported (Ilya);
- use mechanism similar to LINUX_KERNEL_VERSION to also improve USDT code.
====================
Reviewed-by: Stanislav Fomichev <sdf@google.com>
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.