Print thread name when dumping backtrace

Keeping proc interactions isoltated: added function in proc.h/.c
that prints thread name to stdout. It is then used by backtrace.c
directly to keep from having to store the string in memory in
snapshot or any other struct

Author: nslowell

src/backtrace.c

@@ -108,8 +108,10 @@ int backtrace_snapshot(int pid, int *tids, int *index, int nr_tids)
         return -1;
 
     for (i = 0; i < snap->num_threads; ++i) {
-        printf("--------------------  thread %d (%d)  --------------------\n",
+        printf("--------------------  thread %d (%d) (",
                (index != NULL ? index[i] : i+1), snap->tids[i]);
+        print_proc_comm(snap->tids[i]);
+        printf(")  --------------------\n");
 
         snap->cur_thr = i;
         if (backtrace_thread(&snapshot_addr_space_accessors, snap) < 0)
@@ -145,8 +147,10 @@ int backtrace_ptrace(int pid, int *tids, int *index, int nr_tids)
     for (i = 0; i < count; ++i) {
         void *upt_info;
 
-        printf("--------------------  thread %d (%d)  --------------------\n",
+        printf("--------------------  thread %d (%d) (",
                (index != NULL ? index[i] : i+1), threads[i]);
+        print_proc_comm(threads[i]);
+        printf(")  --------------------\n");
 
         if (threads[i] != pid && attach_thread(threads[i]) < 0) {
             rc = -1;

src/proc.c

@@ -191,6 +191,30 @@ int print_proc_maps(int pid)
     return system(cmd);
 }
 
+int print_proc_comm(int pid)
+{
+    FILE *f;
+    char buf[32] = "";
+    int i;
+    int rc = -1;
+
+    snprintf(buf, sizeof(buf), "/proc/%d/comm", pid);
+    if ((f = fopen(buf, "r")) == NULL) {
+        fprintf(stderr, "cannot open %s: %s\n", buf, strerror(errno));
+        return -1;
+    }
+
+    if (fgets(buf, sizeof(buf), f)) {
+        i = strcspn(buf, "\n");
+        buf[i] = '\0';
+        printf("%s", buf);
+        rc = 0;
+    }
+
+    fclose(f);
+    return rc;
+}
+
 /*
  * filter for scandir(). choose only thread identifiers
  */

src/proc.h

@@ -27,6 +27,12 @@ struct mem_map *create_maps(int pid);
  */
 int print_proc_maps(int pid);
 
+/*
+ * simple routine to print process comm for
+ * debugging or advanced error reporting
+ */
+int print_proc_comm(int pid);
+
 /*
  * get thread identifiers of the process
  */