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When run as normal user with default sysctl kernel.kptr_restrict=0 and kernel.perf_event_paranoid=2, perf probe fails with: $ ./perf probe move_page_tables Relocated base symbol is not found! The warning message is not much informative. The reason perf fails is because /proc/kallsyms is restricted by perf_event_paranoid=2 for normal user and thus perf fails to read relocated address of the base symbol. Tweaking kptr_restrict and perf_event_paranoid can change the behavior of perf probe. Also, running as root or privileged user works too. Add these details in the warning message. Plus, kmap->ref_reloc_sym might not be always set even if host_machine is initialized. Above is the example of the same. Remove that comment. Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com> Acked-by: Masami Hiramatsu <mhiramat@kernel.org> Cc: Jiri Olsa <jolsa@redhat.com> Link: http://lore.kernel.org/lkml/20210525043744.193297-1-ravi.bangoria@linux.ibm.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.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.