Support loading elf notes from memfd backed map (iovisor#2314)

* Support loading elf notes from file backed on memfd

* Use const for arguments to _procutils_memfd_path

* Cleanups for procuptils_memfd_path

src/cc/bcc_proc.c

@@ -14,10 +14,8 @@
  * limitations under the License.
  */
 
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/mman.h>
 #include <ctype.h>
+#include <dirent.h>
 #include <fcntl.h>
 #include <limits.h>
 #include <math.h>
@@ -26,6 +24,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 #include <unistd.h>
 
 #include "bcc_perf_map.h"
@@ -82,6 +83,42 @@ int bcc_mapping_is_file_backed(const char *mapname) {
  STARTS_WITH(mapname, "[vsyscall]"));
 }
 
+/*
+Finds a file descriptor for a given inode if it's a memory-backed fd.
+*/
+static char *_procutils_memfd_path(const int pid, const uint64_t inum) {
+ char path_buffer[PATH_MAX + 1];
+ char *path = NULL;
+ char *dirstr;
+ DIR *dirstream;
+ struct stat sb;
+ struct dirent *dent;
+
+ snprintf(path_buffer, (PATH_MAX + 1), "/proc/%d/fd", pid);
+ dirstr = malloc(strlen(path_buffer) + 1);
+ strcpy(dirstr, path_buffer);
+ dirstream = opendir(dirstr);
+
+ if (dirstream == NULL)
+ return NULL;
+
+ while (path == NULL && (dent = readdir(dirstream)) != NULL) {
+ snprintf(path_buffer, (PATH_MAX + 1), "%s/%s", dirstr, dent->d_name);
+ if (stat(path_buffer, &sb) == -1)
+ continue;
+
+ if (sb.st_ino == inum) {
+ char *pid_fd_path = malloc(strlen(path_buffer) + 1);
+ strcpy(pid_fd_path, path_buffer);
+ path = pid_fd_path;
+ }
+ }
+ closedir(dirstream);
+ free(dirstr);
+
+ return path;
+}
+
 int bcc_procutils_each_module(int pid, bcc_procutils_modulecb callback,
  void *payload) {
  char procmap_filename[128];
@@ -112,6 +149,15 @@ int bcc_procutils_each_module(int pid, bcc_procutils_modulecb callback,
  if (!bcc_mapping_is_file_backed(name))
  continue;
 
+ if (strstr(name, "/memfd:")) {
+ char *memfd_name = _procutils_memfd_path(pid, inode);
+ if (memfd_name != NULL) {
+ strcpy(buf, memfd_name);
+ free(memfd_name);
+ name = buf;
+ }
+ }
+
  if (callback(name, begin, end, (uint64_t)offset, true, payload) < 0)
  break;
  }