perf buildid: Fix cpumode of buildid event

There is a nasty confusion that, for kernel module, dso->kernel is not
necessary to be DSO_TYPE_KERNEL or DSO_TYPE_GUEST_KERNEL.  These two
enums are for vmlinux. See thread [1]. We tried to fix this part but it
is costy.

Code machine__write_buildid_table() is another unfortunate function fall
into this trap that, when issuing buildid event for a kernel module,
cpumode it gives to the event is PERF_RECORD_MISC_USER, not
PERF_RECORD_MISC_KERNEL.

However, even with this bug, most of the time it doesn't causes real
problem. I find this issue when trying to use a perf before commit
3d39ac5 ("perf machine: No need to have two DSOs lists") to parse a
perf.data generated by newest perf.

[1] https://lkml.org/lkml/2015/9/21/908

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@redhat.com>
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/1454089251-203152-1-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/build-id.c

@@ -211,6 +211,7 @@ static int machine__write_buildid_table(struct machine *machine, int fd)
  dsos__for_each_with_build_id(pos, &machine->dsos.head) {
  const char *name;
  size_t name_len;
+ bool in_kernel = false;
 
  if (!pos->hit)
  continue;
@@ -227,8 +228,11 @@ static int machine__write_buildid_table(struct machine *machine, int fd)
  name_len = pos->long_name_len + 1;
  }
 
+ in_kernel = pos->kernel ||
+ is_kernel_module(name,
+ PERF_RECORD_MISC_CPUMODE_UNKNOWN);
  err = write_buildid(name, name_len, pos->build_id, machine->pid,
- pos->kernel ? kmisc : umisc, fd);
+ in_kernel ? kmisc : umisc, fd);
  if (err)
  break;
  }