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There 2 problems when reading symbols files: * It doesn't report any errors even if when users specify symbol files which don't exist with --kallsyms or --vmlinux. The result just shows the address without symbols, which is not what is expected. So it's better to report errors and exit the program. * When using command perf report --kallsyms=/proc/kallsyms with a non-root user, symbols are resolved. Then select one symbol and annotate it, it reports the error as the following: Can't annotate __clear_user: No vmlinux file with build id xxx was found. The problem is caused by reading /proc/kcore without access permission. /proc/kcore requires CAP_SYS_RAWIO capability to access, so it needs to change access permission to allow a specific user to read /proc/kcore or use root to execute the perf command. This patch is to report errors when symbol files specified by users don't exist. And check access permission of /proc/kcore when reading it. Signed-off-by: Li Zhang <zhlcindy@linux.vnet.ibm.com> Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1434704253-2632-1-git-send-email-zhlcindy@linux.vnet.ibm.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>