On Wed, 6 Jan 2021 08:09:00 +0800 kernel test robot <lkp@intel.com> wrote:

> Hi Andrey,
>    In file included from arch/x86/boot/compressed/cmdline.c:2:
>    In file included from arch/x86/boot/compressed/misc.h:30:
>    In file included from include/linux/acpi.h:14:
>    In file included from include/linux/resource_ext.h:11:
>    In file included from include/linux/slab.h:136:
> >> include/linux/kasan.h:314:77: warning: non-void function does not return a value [-Wreturn-type]
>    static inline bool kasan_check_byte(const void *address, unsigned long ip) {}
>                                                                                ^
>    1 warning generated.
> 

This?

--- a/include/linux/kasan.h~kasan-fix-bug-detection-via-ksize-for-hw_tags-mode-fix
+++ a/include/linux/kasan.h
@@ -311,7 +311,10 @@ static inline void *kasan_krealloc(const
 	return (void *)object;
 }
 static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
-static inline bool kasan_check_byte(const void *address, unsigned long ip) {}
+static inline bool kasan_check_byte(const void *address, unsigned long ip)
+{
+	return true;
+}
 
 #endif /* CONFIG_KASAN */
 

btw, "kasan_check_byte" isn't a good function name.  Check for what? 
Does it return true for a check which passed, or for a check which
failed?  Something like "kasan_byte_valid" would be better - the name
explains the return value.