kernel: thread: fix warning of always false

K_KERNEL_STACK_RESERVED can be 0 which can give a warning with
-Wtype-limits. Only perform the check if ARCH_KERNEL_STACK_RESERVED
is set. Also remove the the unncessary sets in arch.h where it's
manually set to 0, it defaults to 0 anyways.

Signed-off-by: Ryan McClelland <ryanmcclelland@meta.com>

include/zephyr/arch/x86/thread_stack.h

@@ -107,7 +107,6 @@ struct z_x86_thread_stack_header {
 #define ARCH_KERNEL_STACK_RESERVED	CONFIG_MMU_PAGE_SIZE
 #define ARCH_KERNEL_STACK_OBJ_ALIGN	CONFIG_MMU_PAGE_SIZE
 #else
-#define ARCH_KERNEL_STACK_RESERVED	0
 #define ARCH_KERNEL_STACK_OBJ_ALIGN	ARCH_STACK_PTR_ALIGN
 #endif
 

include/zephyr/arch/xtensa/thread_stack.h

@@ -68,7 +68,6 @@ struct xtensa_thread_stack_header {
 	ROUND_UP((size), XTENSA_STACK_SIZE_ALIGN)
 
 /* kernel stack */
-#define ARCH_KERNEL_STACK_RESERVED		0
 #define ARCH_KERNEL_STACK_OBJ_ALIGN		ARCH_STACK_PTR_ALIGN
 
 #endif /* _ASMLANGUAGE */

kernel/thread.c

@@ -400,6 +400,7 @@ static char *setup_thread_stack(struct k_thread *new_thread,
 		stack_buf_start = K_KERNEL_STACK_BUFFER(stack);
 		stack_buf_size = stack_obj_size - K_KERNEL_STACK_RESERVED;
 
+#if defined(ARCH_KERNEL_STACK_RESERVED)
 		/* Zephyr treats stack overflow as an app bug.  But
 		 * this particular overflow can be seen by static
 		 * analysis so needs to be handled somehow.
@@ -407,7 +408,7 @@ static char *setup_thread_stack(struct k_thread *new_thread,
 		if (K_KERNEL_STACK_RESERVED > stack_obj_size) {
 			k_panic();
 		}
-
+#endif
 	}
 
 #ifdef CONFIG_THREAD_STACK_MEM_MAPPED