This patch allows 'perf script' output messages from BPF program.  For
example, use test_bpf_output_3.c at the end of this commit message,

  # ./perf record -e bpf-output/no-inherit,name=evt/ \
                 -e ./test_bpf_output_3.c/map:channel.event=evt/ \
                 usleep 100000

  # ./perf script
          usleep  4882 21384.532523:                       evt:  ffffffff810e97d1 sys_nanosleep ([kernel.kallsyms])
      BPF output: 0000: 52 61 69 73 65 20 61 20  Raise a
                  0008: 42 50 46 20 65 76 65 6e  BPF even
                  0010: 74 21 00 00              t!..
      BPF string: "Raise a BPF event!"

          usleep  4882 21384.632606:                       evt:  ffffffff8105c609 kretprobe_trampoline_holder ([kernel.kallsyms
      BPF output: 0000: 52 61 69 73 65 20 61 20  Raise a
                  0008: 42 50 46 20 65 76 65 6e  BPF even
                  0010: 74 21 00 00              t!..
      BPF string: "Raise a BPF event!"

Two samples from BPF output are printed by both binary and string
format.

If BPF program output something unprintable, string format is
suppressed.

  /************************ BEGIN **************************/
  #include <uapi/linux/bpf.h>
  struct bpf_map_def {
         unsigned int type;
         unsigned int key_size;
         unsigned int value_size;
         unsigned int max_entries;
  };
  #define SEC(NAME) __attribute__((section(NAME), used))
  static u64 (*ktime_get_ns)(void) =
         (void *)BPF_FUNC_ktime_get_ns;
  static int (*trace_printk)(const char *fmt, int fmt_size, ...) =
         (void *)BPF_FUNC_trace_printk;
  static int (*get_smp_processor_id)(void) =
         (void *)BPF_FUNC_get_smp_processor_id;
  static int (*perf_event_output)(void *, struct bpf_map_def *, int, void *, unsigned long) =
         (void *)BPF_FUNC_perf_event_output;

  struct bpf_map_def SEC("maps") channel = {
         .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
         .key_size = sizeof(int),
         .value_size = sizeof(u32),
         .max_entries = __NR_CPUS__,
  };

  static inline int __attribute__((always_inline))
  func(void *ctx, int type)
  {
         char output_str[] = "Raise a BPF event!";

         perf_event_output(ctx, &channel, get_smp_processor_id(),
                           &output_str, sizeof(output_str));
         return 0;
  }
  SEC("func_begin=sys_nanosleep")
  int func_begin(void *ctx) {return func(ctx, 1);}
  SEC("func_end=sys_nanosleep%return")
  int func_end(void *ctx) { return func(ctx, 2);}
  char _license[] SEC("license") = "GPL";
  int _version SEC("version") = LINUX_VERSION_CODE;
  /************************* END ***************************/
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1456312845-111583-3-git-send-email-wangnan0@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>