Useful for getting stack traces for hardware breakpoint events.

Test result:

Before this patch:
 # ~/perf record -g -e mem:0x600980 ./sample
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 0.011 MB perf.data (12 samples) ]

 # ~/perf script

 # ~/perf script -F comm,tid,pid,time,event,ip,sym,dso
 sample 22520/22520 97457.836294: mem:0x600980:
          5a4ad8 __clear_user (/lib/modules/4.3.0-rc4+/build/vmlinux)
 ...
          3f41ba sys_execve (/lib/modules/4.3.0-rc4+/build/vmlinux)
          979395 return_from_execve (/lib/modules/4.3.0-rc4+/build/vmlinux)
    7f1b59719cf7 [unknown] ([unknown])

 sample 22520/22520 97457.836648: mem:0x600980:
             532 main (/home/w00229757/DataBreakpoints/sample)
           21bd5 __libc_start_main (/tmp/oxygen_root-root/lib64/libc-2.18.so)
 ...

After this patch:
 # ~/perf script
 sample 22520 97457.836294: mem:0x600980:
                   5a4ad8 __clear_user (/lib/modules/4.3.0-rc4+/build/vmlinux)
 ...
                   3f41ba sys_execve (/lib/modules/4.3.0-rc4+/build/vmlinux)
                   979395 return_from_execve (/lib/modules/4.3.0-rc4+/build/vmlinux)
             7f1b59719cf7 [unknown] ([unknown])

 sample 22520 97457.836648: mem:0x600980:
                      532 main (/home/w00229757/DataBreakpoints/sample)
                    21bd5 __libc_start_main (/tmp/oxygen_root-root/lib64/libc-2.18.so)

Committer note:

So, further testing, lets do it for a kernel global variable,
tcp_hashinfo:

  # grep -w tcp_hashinfo /proc/kallsyms
  ffffffff8202fc00 B tcp_hashinfo
  #

Note: allow specifying mem:tcp_hashinfo:

  # perf record -g -e mem:0xffffffff81c65ac0 -a
  ^C[ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.790 MB perf.data ]
  #
  # perf evlist
  mem:0xffffffff8202fc00
  # perf evlist -v
  mem:0xffffffff8202fc00: type: 5, size: 112, { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|CALLCHAIN|CPU, disabled: 1, inherit: 1, mmap: 1, comm: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, bp_type: 3, { bp_addr, config1 }: 0xffffffff8202fc00, { bp_len, config2 }: 0x4
  #

Then, after this patch:

  # perf script
  swapper 0 [000] 171036.986988: mem:0xffffffff8202fc00:
    8a0fb5 __inet_lookup_established (/lib/modules/4.3.0+/build/vmlinux)
    8bc09d tcp_v4_early_demux (/lib/modules/4.3.0+/build/vmlinux)
    896def ip_rcv_finish (/lib/modules/4.3.0+/build/vmlinux)
    8976c2 ip_rcv (/lib/modules/4.3.0+/build/vmlinux)
    855eba __netif_receive_skb_core (/lib/modules/4.3.0+/build/vmlinux)
    8565d8 __netif_receive_skb (/lib/modules/4.3.0+/build/vmlinux)
    8572a8 process_backlog (/lib/modules/4.3.0+/build/vmlinux)
    856b11 net_rx_action (/lib/modules/4.3.0+/build/vmlinux)
    2a284b __do_softirq (/lib/modules/4.3.0+/build/vmlinux)
    2a2ba3 irq_exit (/lib/modules/4.3.0+/build/vmlinux)
    96b7a4 do_IRQ (/lib/modules/4.3.0+/build/vmlinux)
    969807 ret_from_intr (/lib/modules/4.3.0+/build/vmlinux)
    804c27 cpuidle_enter (/lib/modules/4.3.0+/build/vmlinux)
    2ded22 call_cpuidle (/lib/modules/4.3.0+/build/vmlinux)
    2defb6 cpu_startup_entry (/lib/modules/4.3.0+/build/vmlinux)
    95d5bc rest_init (/lib/modules/4.3.0+/build/vmlinux)
   1163ffa start_kernel ([kernel.vmlinux].init.text)
   11634d7 x86_64_start_reservations ([kernel.vmlinux].init.text)
   1163623 x86_64_start_kernel ([kernel.vmlinux].init.text)
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1449541544-67621-16-git-send-email-wangnan0@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>