xtensa: Disable interrupts on entry to _Cstart

Zephyr isn't ready to handle interrupts yet, until the
threading/scheduler are set up and we make our first context switch.
This was a semi-hidden bug: only the timer interrupt would actually
get unmasked before the system was ready, and obviously would never
have time to fire a tick before the system completed initialization.
But a combination of system load and a new version of Qemu (which
seems to be more sensitive to non-deterministic timing glitchery) has
made this visible.  About 2-3% of the time when run under a full
sanitycheck, the qemu process will get swapped away for long enough
that the tick timer expires before _Cstart() has reached
enable_multithreading().

It looks like the original code was cut and pasted from another
implementation, which was expected to call into an "application"
main() routine that wanted interrupts ready.

Fixes #11182

(Note also that this code is not used for ESP-32, which has its own
startup path)

Signed-off-by: Andy Ross <[email protected]>

Author: Andy Ross

arch/xtensa/core/crt1.S

@@ -56,8 +56,7 @@ _start:
 	 *
 	 *  Assumptions on entry to _start:
 	 *	- low (level-one) and medium priority interrupts are disabled
-	 *	  via PS.INTLEVEL and/or INTENABLE (PS.INTLEVEL is expected to
-	 *	  be zeroed, to potentially enable them, before calling main)
+	 *	  via PS.INTLEVEL and/or INTENABLE
 	 *	- C calling context not initialized:
 	 *	  - PS not initialized
 	 *	  - SP not initialized
@@ -88,16 +87,16 @@ _start:
 
 	/*
 	 *  Now that sp (a1) is set, we can set PS as per the application (user
-	 *  vector mode, enable interrupts, enable window exceptions if
+	 *  vector mode, disable interrupts, enable window exceptions if
 	 *  applicable).
 	 */
 #if XCHAL_HAVE_EXCEPTIONS
 # ifdef __XTENSA_CALL0_ABI__
-	/* PS.WOE = 0, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 0 */
-	movi	a3, PS_UM
+	/* PS.WOE = 0, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 15 */
+	movi	a3, PS_UM|PS_INTLEVEL(15)
 # else
-	/* PS.WOE = 1, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 0 */
-	movi	a3, PS_UM|PS_WOE
+	/* PS.WOE = 1, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 15 */
+	movi	a3, PS_UM|PS_WOE|PS_INTLEVEL(15)
 # endif
 	wsr	a3, PS
 	rsync