ACPICA: acpi_pci_routing_table: Replace fixed-size array with flex array member

ACPICA commit f4a3afd78c28dede0907f47951f0b73c9a776d4e

The "Source" array is actually a dynamically sized array, but it
is defined as a fixed-size 4 byte array. This results in tripping
both compile-time and run-time bounds checkers (e.g. via either
__builtin_object_size() or -fsanitize=bounds).

To retain the padding, create a union with an unused Pad variable of
size 4, and redefine Source as a proper flexible array member.

No binary changes appear in the .text nor .data sections.

Link: acpica/acpica@f4a3afd7
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: kees

include/acpi/acrestyp.h

@@ -693,7 +693,10 @@ struct acpi_pci_routing_table {
 	u32 pin;
 	u64 address;		/* here for 64-bit alignment */
 	u32 source_index;
-	char source[4];		/* pad to 64 bits so sizeof() works in all cases */
+	union {
+		char pad[4];	/* pad to 64 bits so sizeof() works in all cases */
+		 ACPI_FLEX_ARRAY(char, source);
+	};
 };
 
 #endif				/* __ACRESTYP_H__ */