x86/EFI: suppress GNU ld 2.36'es creation of base relocs

All of the sudden ld creates base relocations itself, for PE
executables - as a result we now have two of them for every entity to
be relocated. While we will likely want to use this down the road, it
doesn't work quite right yet in corner cases, so rather than suppressing
our own way of creating the relocations we need to tell ld to avoid
doing so.

Probe whether --disable-reloc-section (which was introduced by the same
commit making relocation generation the default) is recognized by ld's PE
emulation, and use the option if so. (To limit redundancy, move the first
part of setting EFI_LDFLAGS earlier, and use it already while probing.)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 76cbb9c3f4
master date: 2021-02-25 15:11:58 +0100

xen/arch/x86/Makefile

@@ -173,8 +173,13 @@ EFI_LDFLAGS += --major-subsystem-version=2 --minor-subsystem-version=0
 # Check if the compiler supports the MS ABI.
 export XEN_BUILD_EFI := $(shell $(CC) $(filter-out $(CFLAGS-y) .%.d,$(CFLAGS)) -c efi/check.c -o efi/check.o 2>/dev/null && echo y)
 # Check if the linker supports PE.
-XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(shell $(LD) -mi386pep --subsystem=10 -S -o efi/check.efi efi/check.o 2>/dev/null && echo y))
+XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(shell $(LD) $(call EFI_LDFLAGS,0x100000000) -o efi/check.efi efi/check.o 2>/dev/null && echo y))
 CFLAGS-$(XEN_BUILD_EFI) += -DXEN_BUILD_EFI
+# Check if the linker produces fixups in PE by default (we need to disable it doing so for now).
+XEN_NO_PE_FIXUPS := $(if $(XEN_BUILD_EFI), \
+                         $(shell $(LD) $(call EFI_LDFLAGS,0x100000000) --disable-reloc-section -o efi/check.efi efi/check.o 2>/dev/null && \
+                                 echo --disable-reloc-section))
+EFI_LDFLAGS += $(XEN_NO_PE_FIXUPS)
 
 $(TARGET).efi: VIRT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A VIRT_START$$,,p')
 $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A ALT_START$$,,p')