Fix for Linux 4.19-rc1 and later kernels that contain kernel commit

2c4704756cab7cfa031ada4dab361562f0e357c0, titled "pids: Move the pgrp
and session pid pointers from task_struct to signal_struct".  Without
the patch, the crash session fails during initialization with the
message "crash: invalid structure member offset: task_struct_pids".
(anderson@redhat.com)

defs.h

@@ -2036,6 +2036,7 @@ struct offset_table {                    /* stash of commonly-used offsets */
 	long memcg_cache_params___root_caches_node;
 	long memcg_cache_params_children;
 	long memcg_cache_params_children_node;
+	long task_struct_pid_links;
 };
 
 struct size_table {         /* stash of commonly-used sizes */

symbols.c

@@ -8606,6 +8606,8 @@ dump_offset_table(char *spec, ulong makestruct)
                 OFFSET(task_rss_stat_count));
         fprintf(fp, "              task_struct_pids: %ld\n",
                 OFFSET(task_struct_pids));
+        fprintf(fp, "         task_struct_pid_links: %ld\n",
+                OFFSET(task_struct_pid_links));
         fprintf(fp, "          task_struct_last_run: %ld\n",
                 OFFSET(task_struct_last_run));
         fprintf(fp, "         task_struct_timestamp: %ld\n",

task.c

@@ -314,6 +314,7 @@ task_init(void)
 	        strcpy(buf, "alias last ps -l");
         	alias_init(buf);
 	}
+	MEMBER_OFFSET_INIT(task_struct_pid_links, "task_struct", "pid_links");
 	MEMBER_OFFSET_INIT(pid_link_pid, "pid_link", "pid");
 	MEMBER_OFFSET_INIT(pid_hash_chain, "pid", "hash_chain");
 
@@ -2382,7 +2383,10 @@ refresh_radix_tree_task_table(void)
 		pid_tasks_0 = ULONG(pidbuf + OFFSET(pid_tasks));
 		if (!pid_tasks_0)
 			continue;
-		task = pid_tasks_0 - OFFSET(task_struct_pids);
+		if (VALID_MEMBER(task_struct_pids))
+			task = pid_tasks_0 - OFFSET(task_struct_pids);
+		else
+			task = pid_tasks_0 - OFFSET(task_struct_pid_links);
 
 		if (CRASHDEBUG(1))
 			console("pid: %lx  ns: %lx  tasks[0]: %lx task: %lx\n",