xtensa: selectively init interrupt stack at boot

During arch_kernel_init(), the interrupt stack is being
initialized. However, if the current in-use stack is
the interrupt stack, it would wipe all the data up to
that point in stack, and might result in crash. So skip
initializing the interrupt stack if the current stack
pointer is within the boundary of interrupt stack.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

arch/xtensa/include/kernel_arch_func.h

@@ -53,8 +53,22 @@ static ALWAYS_INLINE void arch_kernel_init(void)
 	XTENSA_WSR(ZSR_CPU_STR, cpu0);
 
 #ifdef CONFIG_INIT_STACKS
-	memset(Z_KERNEL_STACK_BUFFER(z_interrupt_stacks[0]), 0xAA,
-	       K_KERNEL_STACK_SIZEOF(z_interrupt_stacks[0]));
+	char *stack_start = Z_KERNEL_STACK_BUFFER(z_interrupt_stacks[0]);
+	size_t stack_sz = K_KERNEL_STACK_SIZEOF(z_interrupt_stacks[0]);
+	char *stack_end = stack_start + stack_sz;
+
+	uint32_t sp;
+
+	__asm__ volatile("mov %0, sp" : "=a"(sp));
+
+	/* Only clear the interrupt stack if the current stack pointer
+	 * is not within the interrupt stack. Or else we would be
+	 * wiping the in-use stack.
+	 */
+	if (((uintptr_t)sp < (uintptr_t)stack_start) ||
+	    ((uintptr_t)sp >= (uintptr_t)stack_end)) {
+		memset(stack_start, 0xAA, stack_sz);
+	}
 #endif
 
 #ifdef CONFIG_XTENSA_MMU