• Arnaldo Carvalho de Melo's avatar
    perf tests bpf: Use SyS_epoll_wait alias · c369e0a1
    Arnaldo Carvalho de Melo authored
    Something made the sys_epoll_wait() function alias not to be found in
    the vmlinux DWARF info, being found only in /proc/kallsyms, which made
    the BPF perf tests to fail:
      [root@jouet ~]# perf test BPF
      37: Test BPF filter                                          :
      37.1: Test basic BPF filtering                               : FAILED!
      37.2: Test BPF prologue generation                           : Skip
      37.3: Test BPF relocation checker                            : Skip
      [root@jouet ~]#
    Using -v we can see it is failing to find DWARF info for the probed function,
    sys_epoll_wait, which we can find in /proc/kallsyms but not in vmlinux with
      [root@jouet ~]# grep -w sys_epoll_wait /proc/kallsyms
      ffffffffbd295b50 T sys_epoll_wait
      [root@jouet ~]#
      [root@jouet ~]# readelf -wi /lib/modules/4.7.0+/build/vmlinux | grep -w sys_epoll_wait
      [root@jouet ~]#
    If we try to use perf probe:
    [root@jouet ~]# perf probe sys_epoll_wait
    Failed to find debug information for address ffffffffbd295b50
    Probe point 'sys_epoll_wait' not found.
      Error: Failed to add events.
    [root@jouet ~]#
    It all works if we use SyS_epoll_wait, that is just an alias to the probed
      [root@jouet ~]# grep -i sys_epoll_wait /proc/kallsyms
      ffffffffbd295b50 T SyS_epoll_wait
      ffffffffbd295b50 T sys_epoll_wait
      [root@jouet ~]#
    So use it:
      [root@jouet ~]# perf test BPF
      37: Test BPF filter                                          :
      37.1: Test basic BPF filtering                               : Ok
      37.2: Test BPF prologue generation                           : Ok
      37.3: Test BPF relocation checker                            : Ok
      [root@jouet ~]#
    Further info:
      [root@jouet ~]# gcc --version
      gcc (GCC) 6.1.1 20160621 (Red Hat 6.1.1-3)
      [acme@jouet linux]$ cat /etc/fedora-release
      Fedora release 24 (Twenty Four)
    Investigation as to why it fails is still underway, but it was always
    going from sys_epoll_wait to SyS_epoll_wait when looking up the DWARF
    info in vmlinux, and this is what is breaking now.
    Switching to use SyS_epoll_wait allows this test to proceed and test the
    BPF code it was designed for, so lets have this in to allow passing this
    test while we fix the root cause.
    Cc: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
    Cc: David Ahern <dsahern@gmail.com>
    Cc: Jiri Olsa <jolsa@kernel.org>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Wang Nan <wangnan0@huawei.com>
    Link: http://lkml.kernel.org/n/tip-7hekjp0bodwjbb419sl2b55h@git.kernel.orgSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
bpf-script-example.c 1.27 KB