[PATCH] ACPI: avoid NULL pointer arithmetic

[Arnd Bergmann <arnd@kernel.org>]

From: Arnd Bergmann <arnd@arndb.de>

There are some very old macros for doing an open-coded offsetof() and
cast between pointer and integer in ACPI headers. clang-14 now complains
about these:

drivers/acpi/acpica/tbfadt.c:86:3: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
         ACPI_FADT_OFFSET(pm_timer_block),
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/acpi/actbl.h:376:47: note: expanded from macro 'ACPI_FADT_OFFSET'
 #define ACPI_FADT_OFFSET(f)             (u16) ACPI_OFFSET (struct acpi_table_fadt, f)
                                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/acpi/actypes.h:511:41: note: expanded from macro 'ACPI_OFFSET'
 #define ACPI_OFFSET(d, f)               ACPI_PTR_DIFF (&(((d *) 0)->f), (void *) 0)
                                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/acpi/actypes.h:505:79: note: expanded from macro 'ACPI_PTR_DIFF'
 #define ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8, (a)) - ACPI_CAST_PTR (u8, (b))))
                                                                              ^ ~~~~~~~~~~~~~~~~~~~~~~~
Convert them to the modern equivalents.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/acpi/actypes.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
index 92c71dfce0d5..285bc7b73de3 100644
--- a/include/acpi/actypes.h
+++ b/include/acpi/actypes.h
@@ -507,8 +507,8 @@ typedef u64 acpi_integer;
 /* Pointer/Integer type conversions */
 
 #define ACPI_TO_POINTER(i)              ACPI_CAST_PTR (void, (acpi_size) (i))
-#define ACPI_TO_INTEGER(p)              ACPI_PTR_DIFF (p, (void *) 0)
-#define ACPI_OFFSET(d, f)               ACPI_PTR_DIFF (&(((d *) 0)->f), (void *) 0)
+#define ACPI_TO_INTEGER(p)              ((uintptr_t)(p))
+#define ACPI_OFFSET(d, f)               offsetof(d, f)
 #define ACPI_PHYSADDR_TO_PTR(i)         ACPI_TO_POINTER(i)
 #define ACPI_PTR_TO_PHYSADDR(i)         ACPI_TO_INTEGER(i)
 
-- 
2.29.2