y2038: arm64: Extend sysvipc compat data structures

Both 32-bit amd 64-bit ARM use the asm-generic header files for their
sysvipc data structures, so no special care is needed to make those
work beyond y2038, with the one exception of compat mode: Since there
is no asm-generic definition of the compat mode IPC structures, ARM64
provides its own copy, and we make those match the changes in the native
asm-generic header files.

There is sufficient padding in these data structures to extend all
timestamps to 64 bit, but on big-endian ARM kernels, the padding
is in the wrong place, so the C library has to ensure it reassembles
a 64-bit time_t correctly.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm64/include/asm/compat.h

@@ -181,10 +181,10 @@ struct compat_ipc64_perm {
 
 struct compat_semid64_ds {
 	struct compat_ipc64_perm sem_perm;
-	compat_time_t  sem_otime;
-	compat_ulong_t __unused1;
-	compat_time_t  sem_ctime;
-	compat_ulong_t __unused2;
+	compat_ulong_t sem_otime;
+	compat_ulong_t sem_otime_high;
+	compat_ulong_t sem_ctime;
+	compat_ulong_t sem_ctime_high;
 	compat_ulong_t sem_nsems;
 	compat_ulong_t __unused3;
 	compat_ulong_t __unused4;
@@ -192,12 +192,12 @@ struct compat_semid64_ds {
 
 struct compat_msqid64_ds {
 	struct compat_ipc64_perm msg_perm;
-	compat_time_t  msg_stime;
-	compat_ulong_t __unused1;
-	compat_time_t  msg_rtime;
-	compat_ulong_t __unused2;
-	compat_time_t  msg_ctime;
-	compat_ulong_t __unused3;
+	compat_ulong_t msg_stime;
+	compat_ulong_t msg_stime_high;
+	compat_ulong_t msg_rtime;
+	compat_ulong_t msg_rtime_high;
+	compat_ulong_t msg_ctime;
+	compat_ulong_t msg_ctime_high;
 	compat_ulong_t msg_cbytes;
 	compat_ulong_t msg_qnum;
 	compat_ulong_t msg_qbytes;
@@ -210,12 +210,12 @@ struct compat_msqid64_ds {
 struct compat_shmid64_ds {
 	struct compat_ipc64_perm shm_perm;
 	compat_size_t  shm_segsz;
-	compat_time_t  shm_atime;
-	compat_ulong_t __unused1;
-	compat_time_t  shm_dtime;
-	compat_ulong_t __unused2;
-	compat_time_t  shm_ctime;
-	compat_ulong_t __unused3;
+	compat_ulong_t shm_atime;
+	compat_ulong_t shm_atime_high;
+	compat_ulong_t shm_dtime;
+	compat_ulong_t shm_dtime_high;
+	compat_ulong_t shm_ctime;
+	compat_ulong_t shm_ctime_high;
 	compat_pid_t   shm_cpid;
 	compat_pid_t   shm_lpid;
 	compat_ulong_t shm_nattch;