s390/traps: add struct to access transactional diagnostic block

gcc-11 warns:

arch/s390/kernel/traps.c: In function __do_pgm_check:
arch/s390/kernel/traps.c:319:17: warning: memcpy reading 256 bytes from a region of size 0 [-Wstringop-overread]
  319 |                 memcpy(&current->thread.trap_tdb, &S390_lowcore.pgm_tdb, 256);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this by adding a struct pgm_tdb to struct lowcore and copy that.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/lowcore.h

@@ -17,6 +17,10 @@
 #define LC_ORDER 1
 #define LC_PAGES 2
 
+struct pgm_tdb {
+	u64 data[32];
+};
+
 struct lowcore {
 	__u8	pad_0x0000[0x0014-0x0000];	/* 0x0000 */
 	__u32	ipl_parmblock_ptr;		/* 0x0014 */
@@ -184,7 +188,7 @@ struct lowcore {
 	__u8	pad_0x1400[0x1800-0x1400];	/* 0x1400 */
 
 	/* Transaction abort diagnostic block */
-	__u8	pgm_tdb[256];			/* 0x1800 */
+	struct pgm_tdb pgm_tdb;			/* 0x1800 */
 	__u8	pad_0x1900[0x2000-0x1900];	/* 0x1900 */
 } __packed __aligned(8192);
 

arch/s390/include/asm/processor.h

@@ -129,7 +129,7 @@ struct thread_struct {
 	struct runtime_instr_cb *ri_cb;
 	struct gs_cb *gs_cb;			/* Current guarded storage cb */
 	struct gs_cb *gs_bc_cb;			/* Broadcast guarded storage cb */
-	unsigned char trap_tdb[256];		/* Transaction abort diagnose block */
+	struct pgm_tdb trap_tdb;		/* Transaction abort diagnose block */
 	/*
 	 * Warning: 'fpu' is dynamically-sized. It *MUST* be at
 	 * the end.

arch/s390/kernel/ptrace.c

@@ -975,10 +975,12 @@ static int s390_tdb_get(struct task_struct *target,
 			struct membuf to)
 {
 	struct pt_regs *regs = task_pt_regs(target);
+	size_t size;
 
 	if (!(regs->int_code & 0x200))
 		return -ENODATA;
-	return membuf_write(&to, target->thread.trap_tdb, 256);
+	size = sizeof(target->thread.trap_tdb.data);
+	return membuf_write(&to, target->thread.trap_tdb.data, size);
 }
 
 static int s390_tdb_set(struct task_struct *target,

arch/s390/kernel/traps.c

@@ -36,7 +36,7 @@ static inline void __user *get_trap_ip(struct pt_regs *regs)
 	unsigned long address;
 
 	if (regs->int_code & 0x200)
-		address = *(unsigned long *)(current->thread.trap_tdb + 24);
+		address = current->thread.trap_tdb.data[3];
 	else
 		address = regs->psw.addr;
 	return (void __user *) (address - (regs->int_code >> 16));
@@ -318,7 +318,7 @@ void noinstr __do_pgm_check(struct pt_regs *regs)
 
 	if (S390_lowcore.pgm_code & 0x0200) {
 		/* transaction abort */
-		memcpy(&current->thread.trap_tdb, &S390_lowcore.pgm_tdb, 256);
+		current->thread.trap_tdb = S390_lowcore.pgm_tdb;
 	}
 
 	if (S390_lowcore.pgm_code & PGM_INT_CODE_PER) {