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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>
41ca1d1e88