gcore: Fix the invalid struct size failure of pid_link on 4.19 and ne…

…wer kernel.

On 4.19 and newer kernel, gcore command fails as following:

===========================================================
    gcore: invalid structure size: pid_link
           FILE: libgcore/gcore_coredump_table.c  LINE: 423  FUNCTION: pid_alive()

    [./crash] error trace: 7f4a7a6762b8 => 7f4a7a676e0f => 53b391 => 53b316

      53b316: SIZE_verify.part.31+70
      53b391: SIZE_verify+49

    gcore: invalid structure size: pid_link
           FILE: libgcore/gcore_coredump_table.c  LINE: 423  FUNCTION: pid_alive()

    Failed.
===========================================================

That is because struct pid_link is removed and struct pid array is added to
struct signal_struct by commit 2c4704756cab ("pids: Move the pgrp and session
pid pointers from task_struct to signal_struct").

Get the pointer of struct pid from task_struct->thread_pid or
signal_struct->pids[] to fix the failure.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1722726

Signed-off-by: Masayoshi Mizuma <[email protected]>

src/gcore.c

@@ -505,6 +505,10 @@ static void gcore_offset_table_init(void)
 		GCORE_ANON_MEMBER_OFFSET_INIT(thread_struct_fpsimd_state, "thread_struct", "uw.fpsimd_state");
 		GCORE_ANON_MEMBER_OFFSET_INIT(thread_struct_tp_value, "thread_struct", "uw.tp_value");
 	}
+	if (MEMBER_EXISTS("task_struct", "thread_pid"))
+		GCORE_MEMBER_OFFSET_INIT(task_struct_thread_pid, "task_struct", "thread_pid");
+	if (MEMBER_EXISTS("signal_struct", "pids"))
+		GCORE_MEMBER_OFFSET_INIT(signal_struct_pids, "signal_struct", "pids");
 }
 
 static void gcore_size_table_init(void)

src/libgcore/gcore_coredump_table.c

@@ -224,7 +224,7 @@ __task_pid_nr_ns(ulong task, enum pid_type type)
 		sizeof(ns), "__task_pid_nr_ns: ns", gcore_verbose_error_handle());
 
 	if (pid_alive(task)) {
-		ulong pids_type_pid;
+		ulong pids_type_pid, signal;
 
                 if (type != PIDTYPE_PID)
 			readmem(task + MEMBER_OFFSET("task_struct",
@@ -233,10 +233,34 @@ __task_pid_nr_ns(ulong task, enum pid_type type)
 				"__task_pid_nr_ns: group_leader",
 				gcore_verbose_error_handle());
 
-		readmem(task + OFFSET(task_struct_pids) + type * SIZE(pid_link)
-			+ OFFSET(pid_link_pid), KVADDR, &pids_type_pid,
-			sizeof(pids_type_pid),
-			"__task_pid_nr_ns: pids_type_pid", gcore_verbose_error_handle());
+		if (VALID_MEMBER(task_struct_pids))
+			readmem(task + OFFSET(task_struct_pids) +
+				type * SIZE(pid_link) + OFFSET(pid_link_pid),
+				KVADDR, &pids_type_pid,
+				sizeof(pids_type_pid),
+				"__task_pid_nr_ns: pids_type_pid",
+				gcore_verbose_error_handle());
+		else
+			if (type == PIDTYPE_PID)
+				readmem(task + GCORE_OFFSET(task_struct_thread_pid),
+					KVADDR, &pids_type_pid,
+					sizeof(pids_type_pid),
+					"__task_pid_nr_ns: pids_type_pid",
+					gcore_verbose_error_handle());
+			else {
+				readmem(task + OFFSET(task_struct_signal),
+					KVADDR, &signal,
+					sizeof(signal),
+					"__task_pid_nr_ns: signal",
+					gcore_verbose_error_handle());
+
+				readmem(signal + GCORE_OFFSET(signal_struct_pids) +
+					type * sizeof(void *),
+					KVADDR, &pids_type_pid,
+					sizeof(pids_type_pid),
+					"__task_pid_nr_ns: pids_type_pid",
+					gcore_verbose_error_handle());
+			}
 
 		nr = pid_nr_ns(pids_type_pid, ns);
         }
@@ -420,9 +444,17 @@ pid_alive(ulong task)
 {
 	pid_t pid;
 
-	readmem(task + OFFSET(task_struct_pids) + PIDTYPE_PID * SIZE(pid_link)
-		+ OFFSET(pid_link_pid), KVADDR, &pid, sizeof(pid), "pid_alive",
-		gcore_verbose_error_handle());
+	if (VALID_MEMBER(task_struct_pids))
+		readmem(task + OFFSET(task_struct_pids) +
+			PIDTYPE_PID * SIZE(pid_link) + OFFSET(pid_link_pid),
+			KVADDR, &pid, sizeof(pid),
+			"pid_alive",
+			gcore_verbose_error_handle());
+	else
+		readmem(task + GCORE_OFFSET(task_struct_thread_pid),
+			KVADDR, &pid, sizeof(pid),
+			"task_struct.thread_pid",
+			gcore_verbose_error_handle());
 
         return !!pid;
 }

src/libgcore/gcore_defs.h

@@ -1077,6 +1077,7 @@ struct gcore_offset_table
 	long sched_entity_sum_exec_runtime;
 	long signal_struct_cutime;
 	long signal_struct_pgrp;
+	long signal_struct_pids;
 	long signal_struct_session;
 	long signal_struct_stime;
 	long signal_struct_sum_sched_runtime;
@@ -1090,6 +1091,7 @@ struct gcore_offset_table
 	long task_struct_static_prio;
 	long task_struct_uid;
 	long task_struct_used_math;
+	long task_struct_thread_pid;
 	long thread_info_status;
 	long thread_info_fpstate;
 	long thread_info_vfpstate;