xen: reuse x86 EFI stub functions for Arm

x86 is using compiler feature testing to decide EFI build
enable or not. When EFI build is disabled, x86 will use an
efi/stub.c file to replace efi/runtime.c for build objects.
Following this idea, we introduce a stub file for Arm, but
use CONFIG_ARM_EFI to decide EFI build enable or not.

And the most functions in x86 EFI stub.c can be reused for
other architectures, like Arm. So we move them to common
and keep the x86 specific function in x86/efi/stub.c.

To avoid the symbol link conflict error when linking common
stub files to x86/efi. We add a regular file check in efi
stub files' link script. Depends on this check we can bypass
the link behaviors for existed stub files in x86/efi.

As there is no Arm specific EFI stub function for Arm in
current stage, Arm still can use the existed symbol link
method for EFI stub files.

Signed-off-by: Wei Chen <wei.chen@arm.com>
Tested-by: Jiamei Xie <jiamei.xie@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/arm/Kconfig

@@ -6,6 +6,7 @@ config ARM_64
 	def_bool y
 	depends on !ARM_32
 	select 64BIT
+	select ARM_EFI
 	select HAS_FAST_MULTIPLY
 
 config ARM
@@ -34,6 +35,9 @@ config ACPI
 	  Advanced Configuration and Power Interface (ACPI) support for Xen is
 	  an alternative to device tree on ARM64.
 
+config ARM_EFI
+	bool
+
 config GICV3
 	bool "GICv3 driver"
 	depends on ARM_64 && !NEW_VGIC

xen/arch/arm/Makefile

@@ -1,6 +1,5 @@
 obj-$(CONFIG_ARM_32) += arm32/
 obj-$(CONFIG_ARM_64) += arm64/
-obj-$(CONFIG_ARM_64) += efi/
 obj-$(CONFIG_ACPI) += acpi/
 obj-$(CONFIG_HAS_PCI) += pci/
 ifneq ($(CONFIG_NO_PLAT),y)
@@ -20,6 +19,7 @@ obj-y += domain.o
 obj-y += domain_build.init.o
 obj-y += domctl.o
 obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
+obj-y += efi/
 obj-y += gic.o
 obj-y += gic-v2.o
 obj-$(CONFIG_GICV3) += gic-v3.o

xen/arch/arm/efi/Makefile

@@ -1,4 +1,12 @@
 include $(srctree)/common/efi/efi-common.mk
 
+ifeq ($(CONFIG_ARM_EFI),y)
 obj-y += $(EFIOBJ-y)
 obj-$(CONFIG_ACPI) +=  efi-dom0.init.o
+else
+# Add stub.o to EFIOBJ-y to re-use the clean-files in
+# efi-common.mk. Otherwise the link of stub.c in arm/efi
+# will not be cleaned in "make clean".
+EFIOBJ-y += stub.o
+obj-y += stub.o
+endif

xen/arch/x86/efi/stub.c

@@ -1,7 +1,5 @@
 #include <xen/efi.h>
-#include <xen/errno.h>
 #include <xen/init.h>
-#include <xen/lib.h>
 #include <asm/asm_defns.h>
 #include <asm/efibind.h>
 #include <asm/page.h>
@@ -10,6 +8,7 @@
 #include <efi/eficon.h>
 #include <efi/efidevp.h>
 #include <efi/efiapi.h>
+#include "../../../common/efi/stub.c"
 
 /*
  * Here we are in EFI stub. EFI calls are not supported due to lack
@@ -45,11 +44,6 @@ void __init noreturn efi_multiboot2(EFI_HANDLE ImageHandle,
     unreachable();
 }
 
-bool efi_enabled(unsigned int feature)
-{
-    return false;
-}
-
 void __init efi_init_memory(void) { }
 
 bool efi_boot_mem_unused(unsigned long *start, unsigned long *end)
@@ -62,32 +56,8 @@ bool efi_boot_mem_unused(unsigned long *start, unsigned long *end)
 
 void efi_update_l4_pgtable(unsigned int l4idx, l4_pgentry_t l4e) { }
 
-bool efi_rs_using_pgtables(void)
-{
-    return false;
-}
-
-unsigned long efi_get_time(void)
-{
-    BUG();
-    return 0;
-}
-
-void efi_halt_system(void) { }
-void efi_reset_system(bool warm) { }
-
-int efi_get_info(uint32_t idx, union xenpf_efi_info *info)
-{
-    return -ENOSYS;
-}
-
 int efi_compat_get_info(uint32_t idx, union compat_pf_efi_info *)
     __attribute__((__alias__("efi_get_info")));
 
-int efi_runtime_call(struct xenpf_efi_runtime_call *op)
-{
-    return -ENOSYS;
-}
-
 int efi_compat_runtime_call(struct compat_pf_efi_runtime_call *)
     __attribute__((__alias__("efi_runtime_call")));

xen/common/efi/efi-common.mk

@@ -9,7 +9,8 @@ CFLAGS-y += -iquote $(srcdir)
 # e.g.: It transforms "dir/foo/bar" into successively
 #       "dir foo bar", ".. .. ..", "../../.."
 $(obj)/%.c: $(srctree)/common/efi/%.c FORCE
-	$(Q)ln -nfs $(subst $(space),/,$(patsubst %,..,$(subst /, ,$(obj))))/source/common/efi/$(<F) $@
+	$(Q)test -f $@ || \
+	    ln -nfs $(subst $(space),/,$(patsubst %,..,$(subst /, ,$(obj))))/source/common/efi/$(<F) $@
 
 clean-files += $(patsubst %.o, %.c, $(EFIOBJ-y:.init.o=.o) $(EFIOBJ-))
 

xen/common/efi/stub.c

@@ -0,0 +1,32 @@
+#include <xen/efi.h>
+#include <xen/errno.h>
+#include <xen/lib.h>
+
+bool efi_enabled(unsigned int feature)
+{
+    return false;
+}
+
+bool efi_rs_using_pgtables(void)
+{
+    return false;
+}
+
+unsigned long efi_get_time(void)
+{
+    BUG();
+    return 0;
+}
+
+void efi_halt_system(void) { }
+void efi_reset_system(bool warm) { }
+
+int efi_get_info(uint32_t idx, union xenpf_efi_info *info)
+{
+    return -ENOSYS;
+}
+
+int efi_runtime_call(struct xenpf_efi_runtime_call *op)
+{
+    return -ENOSYS;
+}