Fixes for address calculation

The calculation of function address in non-shared libraries was
incorrect. Fix it.

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>
diff --git a/src/cc/libbpf.c b/src/cc/libbpf.c
index 4165911..4a5c083 100644
--- a/src/cc/libbpf.c
+++ b/src/cc/libbpf.c
@@ -234,7 +234,7 @@
   attr.wakeup_events = 1;
   pfd = syscall(__NR_perf_event_open, &attr, pid, cpu, group_fd, PERF_FLAG_FD_CLOEXEC);
   if (pfd < 0) {
-    perror("perf_event_open");
+    fprintf(stderr, "perf_event_open(%s/id): %s\n", event_path, strerror(errno));
     goto error;
   }
   perf_reader_set_fd(reader, pfd);