watchdog: diag288_wdt: get rid of register asm

Using register asm statements has been proven to be very error prone,
especially when using code instrumentation where gcc may add function
calls, which clobbers register contents in an unexpected way.

Therefore, get rid of register asm statements in watchdog code, and make
sure this bug class cannot happen.

Moreover, remove the register r1 from the clobber list because this
register is not changed by DIAG 288.
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230203073958.1585738-2-egorenar@linux.ibm.comSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

drivers/watchdog/diag288_wdt.c

@@ -73,20 +73,19 @@ MODULE_ALIAS("vmwatchdog");
 static int __diag288(unsigned int func, unsigned int timeout,
 		     unsigned long action, unsigned int len)
 {
-	register unsigned long __func asm("2") = func;
-	register unsigned long __timeout asm("3") = timeout;
-	register unsigned long __action asm("4") = action;
-	register unsigned long __len asm("5") = len;
+	union register_pair r1 = { .even = func, .odd = timeout, };
+	union register_pair r3 = { .even = action, .odd = len, };
 	int err;
 
 	err = -EINVAL;
 	asm volatile(
-		"	diag	%1, %3, 0x288\n"
-		"0:	la	%0, 0\n"
+		"	diag	%[r1],%[r3],0x288\n"
+		"0:	la	%[err],0\n"
 		"1:\n"
 		EX_TABLE(0b, 1b)
-		: "+d" (err) : "d"(__func), "d"(__timeout),
-		  "d"(__action), "d"(__len) : "1", "cc", "memory");
+		: [err] "+d" (err)
+		: [r1] "d" (r1.pair), [r3] "d" (r3.pair)
+		: "cc", "memory");
 	return err;
 }