xtensa: only use BREAK if explicitly enabled

Introduce CONFIG_XTENSA_BREAK_ON_UNRECOVERABLE_EXCEPTIONS to
use BREAK instruction for unrecoverable exceptions. This
definitely requires debugger to be attached to the hardware
or simulator to catch that.

Also move the infinite loop to NOT result in an infinite
interrupt storm as the debug interrupt will be triggered over
and over again. Same for the simcall exit as it does not
need to be called repetitively.

Signed-off-by: Daniel Leung <[email protected]>

arch/xtensa/Kconfig

@@ -103,6 +103,13 @@ config XTENSA_NUM_SPIN_RELAX_NOPS
 	  Specify the number of NOPs in Xtensa specific
 	  arch_spin_relax().
 
+config XTENSA_BREAK_ON_UNRECOVERABLE_EXCEPTIONS
+	bool "Use BREAK instruction on unrecoverable exceptions"
+	help
+	  Use BREAK instruction when unrecoverable exceptions are
+	  encountered. This requires a debugger attached to catch
+	  the BREAK.
+
 menu "Xtensa HiFi Options"
 
 config XTENSA_CPU_HAS_HIFI

arch/xtensa/core/xtensa_asm2_util.S

@@ -503,8 +503,13 @@ _DoubleExceptionVector:
 	j _Level1Vector
 #else
 
-#if defined(CONFIG_SIMULATOR_XTENSA) || defined(XT_SIMULATOR)
-1:
+#if XCHAL_HAVE_DEBUG && defined(CONFIG_XTENSA_BREAK_ON_UNRECOVERABLE_EXCEPTIONS)
+	/* Signals an unhandled double exception, and unrecoverable exceptions.
+	 * Definitely needs debugger to be attached to the hardware or simulator
+	 * to catch this.
+	 */
+	break	1, 4
+#elif defined(CONFIG_SIMULATOR_XTENSA) || defined(XT_SIMULATOR)
 /* Tell simulator to stop executing here, instead of trying to do
  * an infinite loop (see below). Greatly help with using tracing in
  * simulator so that traces will not have infinite iterations of
@@ -513,12 +518,8 @@ _DoubleExceptionVector:
 	movi a3, 1
 	movi a2, SYS_exit
 	simcall
-#elif XCHAL_HAVE_DEBUG
-/* Signals an unhandled double exception */
-1:	break	1, 4
-#else
-1:
 #endif
+1:
 	j	1b
 #endif /* CONFIG_XTENSA_MMU */