arm64/efi: move arm64 specific stub C code to libstub

Now that we added special handling to the C files in libstub, move
the one remaining arm64 specific EFI stub C file to libstub as
well, so that it gets the same treatment. This should prevent future
changes from resulting in binaries that may execute incorrectly in
UEFI context.

With efi-entry.S the only remaining EFI stub source file under
arch/arm64, we can also simplify the Makefile logic somewhat.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/Makefile

@@ -4,11 +4,8 @@
 
 CPPFLAGS_vmlinux.lds	:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 AFLAGS_head.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
-CFLAGS_efi-stub.o 	:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 CFLAGS_armv8_deprecated.o := -I$(src)
 
-KASAN_SANITIZE_efi-stub.o	:= n
-
 CFLAGS_REMOVE_ftrace.o = -pg
 CFLAGS_REMOVE_insn.o = -pg
 CFLAGS_REMOVE_return_address.o = -pg
@@ -22,9 +19,7 @@ arm64-obj-y		:= debug-monitors.o entry.o irq.o fpsimd.o		\
 			   cpufeature.o alternative.o cacheinfo.o		\
 			   smp.o smp_spin_table.o topology.o
 
-stub-obj				:= efi-stub.o efi-entry.o
-extra-y					:= $(stub-obj)
-stub-obj				:= $(patsubst %.o,%.stub.o,$(stub-obj))
+extra-$(CONFIG_EFI)			:= efi-entry.o
 
 OBJCOPYFLAGS := --prefix-symbols=__efistub_
 $(obj)/%.stub.o: $(obj)/%.o FORCE
@@ -42,7 +37,7 @@ arm64-obj-$(CONFIG_CPU_PM)		+= sleep.o suspend.o
 arm64-obj-$(CONFIG_CPU_IDLE)		+= cpuidle.o
 arm64-obj-$(CONFIG_JUMP_LABEL)		+= jump_label.o
 arm64-obj-$(CONFIG_KGDB)		+= kgdb.o
-arm64-obj-$(CONFIG_EFI)			+= efi.o $(stub-obj)
+arm64-obj-$(CONFIG_EFI)			+= efi.o efi-entry.stub.o
 arm64-obj-$(CONFIG_PCI)			+= pci.o
 arm64-obj-$(CONFIG_ARMV8_DEPRECATED)	+= armv8_deprecated.o
 arm64-obj-$(CONFIG_ACPI)		+= acpi.o

drivers/firmware/efi/libstub/Makefile

@@ -34,6 +34,9 @@ $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
 lib-$(CONFIG_EFI_ARMSTUB)	+= arm-stub.o fdt.o string.o \
 				   $(patsubst %.c,lib-%.o,$(arm-deps))
 
+lib-$(CONFIG_ARM64)		+= arm64-stub.o
+CFLAGS_arm64-stub.o 		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
+
 #
 # arm64 puts the stub in the kernel proper, which will unnecessarily retain all
 # code indefinitely unless it is annotated as __init/__initdata/__initconst etc.