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[Xen-devel] [PATCH] x86/efi: move the logic to detect PE build support

So that it can be used by other components apart from the efi specific

This is required so that the conditional used to define the efi symbol
in the linker script can be removed and instead the definition of the
efi symbol can be guarded using the preprocessor.

The motivation behind this change is to be able to build Xen using lld
(the LLVM linker), that at least on version 6.0.0 doesn't work
properly with a DEFINED being used in a conditional expression:

ld    -melf_x86_64_fbsd  -T xen.lds -N prelink.o --build-id=sha1 \
    /root/src/xen/xen/common/symbols-dummy.o -o /root/src/xen/xen/.xen-syms.0
ld: error: xen.lds:233: symbol not found: efi

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
 xen/arch/x86/Makefile     | 10 ++++++++++
 xen/arch/x86/efi/Makefile | 11 +++--------
 xen/arch/x86/xen.lds.S    |  4 +++-
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 5563c813dd..59f96626aa 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -168,6 +168,16 @@ $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) 
efi/relocs-dummy.o | sed -n 's, A ALT_
 # Don't use $(wildcard ...) here - at least make 3.80 expands this too early!
 $(TARGET).efi: guard = $(if $(shell echo efi/dis* | grep disabled),:)
+# Check if the build system supports PE.
+efi := y$(shell rm -f efi/disabled)
+efi := $(if $(efi),$(shell $(CC) $(filter-out $(CFLAGS-y) .%.d,$(CFLAGS)) -c 
efi/check.c -o efi/check.o 2>efi/disabled && echo y))
+efi := $(if $(efi),$(shell $(LD) -mi386pep --subsystem=10 -o efi/check.efi 
efi/check.o 2>efi/disabled && echo y))
+efi := $(if $(efi),$(shell rm efi/disabled)y)
+export BUILD_PE := $(efi)
+ifeq ($(efi),y)
 ifneq ($(build_id_linker),)
 ifeq ($(call ld-ver-build-id,$(LD) $(filter -m%,$(EFI_LDFLAGS))),y)
diff --git a/xen/arch/x86/efi/Makefile b/xen/arch/x86/efi/Makefile
index 3be9661108..ff5e33fb25 100644
--- a/xen/arch/x86/efi/Makefile
+++ b/xen/arch/x86/efi/Makefile
@@ -1,16 +1,11 @@
 CFLAGS += -fshort-wchar
-efi := y$(shell rm -f disabled)
-efi := $(if $(efi),$(shell $(CC) $(filter-out $(CFLAGS-y) .%.d,$(CFLAGS)) -c 
check.c 2>disabled && echo y))
-efi := $(if $(efi),$(shell $(LD) -mi386pep --subsystem=10 -o check.efi check.o 
2>disabled && echo y))
-efi := $(if $(efi),$(shell rm disabled)y)
 %.o: %.ihex
        $(OBJCOPY) -I ihex -O binary $< $@
 boot.init.o: buildid.o
 obj-y := stub.o
-obj-$(efi) := boot.init.o compat.o relocs-dummy.o runtime.o
-extra-$(efi) += buildid.o
-nocov-$(efi) += stub.o
+obj-$(BUILD_PE) := boot.init.o compat.o relocs-dummy.o runtime.o
+extra-$(BUILD_PE) += buildid.o
+nocov-$(BUILD_PE) += stub.o
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 326e885402..f93d5d7e16 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -304,7 +304,9 @@ SECTIONS
   } :text
-  efi = DEFINED(efi) ? efi : .;
+#ifndef BUILD_PE
+  efi = .;
   /* Sections to be discarded */
   /DISCARD/ : {

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