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When debugging a crash that appears to be related to ftrace, but not for sure, it is useful to know if a function was ever enabled by ftrace or not. It could be that a BPF program was attached to it, or possibly a live patch. We are having crashes in the field where this information is not always known. But having ftrace set a flag if a function has ever been attached since boot up helps tremendously in trying to know if a crash had to do with something using ftrace. For analyzing crashes, the use of a kdump image can have access to the flags. When looking at issues where the kernel did not panic, the touched_functions file can simply be used. Link: https://lore.kernel.org/linux-trace-kernel/20230124095653.6fd1640e@gandalf.local.home Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Tested-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Chris Li <chriscli@google.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.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.