x86/EFI: avoid use of GNU ld's --disable-reloc-section when possible

As of commit 6fa7408d72b3 ("ld: don't generate base relocations in PE
output for absolute symbols") I'm feeling sufficiently confident in GNU
ld to use its logic for generating base relocations, which was enabled
for executables at some point last year (prior to that this would have
got done only for DLLs).

GNU ld, seeing the original relocations coming from the ELF object files,
generates different relocation types for our page tables (64-bit ones,
while mkreloc produces 32-bit ones). This requires also permitting and
handling that type in efi_arch_relocate_image().

Note that in the case that we leave base relocation generation to ld,
while efi/relocs-dummy.o then won't be linked into any executable
anymore, it still needs generating (and hence dependencies need to be
kept as they are) in order to have VIRT_BASE pulled out of it.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index b224b1cf89d2e18a912bae2b5ecdf4b02d7b1d71..5b47206ad181463241f0a0d6efcbf03f5e72bac8 100644 (file)
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -123,18 +123,37 @@ $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
        mv $(TMP) $(TARGET)
 
 ifneq ($(efi-y),)
+
 # Check if the compiler supports the MS ABI.
 export XEN_BUILD_EFI := $(shell $(CC) $(XEN_CFLAGS) -c efi/check.c -o efi/check.o 2>/dev/null && echo y)
+CFLAGS-$(XEN_BUILD_EFI) += -DXEN_BUILD_EFI
+
 # Check if the linker supports PE.
 EFI_LDFLAGS = $(patsubst -m%,-mi386pep,$(XEN_LDFLAGS)) --subsystem=10 --strip-debug
 XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(shell $(LD) $(EFI_LDFLAGS) -o efi/check.efi efi/check.o 2>/dev/null && echo y))
-CFLAGS-$(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) $(EFI_LDFLAGS) --disable-reloc-section -o efi/check.efi efi/check.o 2>/dev/null && \
-                                 echo --disable-reloc-section))
+
+ifeq ($(XEN_BUILD_PE),y)
+
+# Check if the linker produces fixups in PE by default
+nr-fixups := $(shell $(OBJDUMP) -p efi/check.efi | grep '^[[:blank:]]*reloc[[:blank:]]*[0-9][[:blank:]].*DIR64$$' | wc -l)
+ifeq ($(nr-fixups),2)
+MKRELOC := :
+relocs-dummy :=
+else
+MKRELOC := efi/mkreloc
+relocs-dummy := efi/relocs-dummy.o
+# If the linker produced fixups but not precisely two of them, we need to
+# disable it doing so.  But if it didn't produce any fixups, it also wouldn't
+# recognize the option.
+ifneq ($(nr-fixups),0)
+EFI_LDFLAGS += --disable-reloc-section
+endif
 endif
 
+endif # $(XEN_BUILD_PE)
+
+endif # $(efi-y)
+
 ALL_OBJS := $(BASEDIR)/arch/x86/boot/built_in.o $(BASEDIR)/arch/x86/efi/built_in.o $(ALL_OBJS)
 
 ifeq ($(CONFIG_LTO),y)
@@ -178,7 +197,7 @@ note.o: $(TARGET)-syms
                --rename-section=.data=.note.gnu.build-id -S $@.bin $@
        rm -f $@.bin
 
-EFI_LDFLAGS += --image-base=$(1) --stack=0,0 --heap=0,0 $(XEN_NO_PE_FIXUPS)
+EFI_LDFLAGS += --image-base=$(1) --stack=0,0 --heap=0,0
 EFI_LDFLAGS += --section-alignment=0x200000 --file-alignment=0x20
 EFI_LDFLAGS += --major-image-version=$(XEN_VERSION)
 EFI_LDFLAGS += --minor-image-version=$(XEN_SUBVERSION)
@@ -192,7 +211,11 @@ EFI_LDFLAGS += --no-insert-timestamp
 endif
 
 $(TARGET).efi: VIRT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A VIRT_START$$,,p')
+ifeq ($(MKRELOC),:)
+$(TARGET).efi: ALT_BASE :=
+else
 $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A ALT_START$$,,p')
+endif
 
 ifneq ($(build_id_linker),)
 ifeq ($(call ld-ver-build-id,$(LD) $(filter -m%,$(EFI_LDFLAGS))),y)
@@ -213,16 +236,16 @@ note_file_option ?= $(note_file)
 ifeq ($(XEN_BUILD_PE),y)
 $(TARGET).efi: prelink.o $(note_file) efi.lds efi/relocs-dummy.o efi/mkreloc
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
-                 $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< efi/relocs-dummy.o \
+                 $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< $(relocs-dummy) \
                        $(BASEDIR)/common/symbols-dummy.o $(note_file_option) -o $(@D)/.$(@F).$(base).0 &&) :
-       efi/mkreloc $(foreach base,$(VIRT_BASE) $(ALT_BASE),$(@D)/.$(@F).$(base).0) >$(@D)/.$(@F).0r.S
+       $(MKRELOC) $(foreach base,$(VIRT_BASE) $(ALT_BASE),$(@D)/.$(@F).$(base).0) >$(@D)/.$(@F).0r.S
        $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).0 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort >$(@D)/.$(@F).0s.S
        $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0r.o $(@D)/.$(@F).0s.o
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
                  $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< \
                        $(@D)/.$(@F).0r.o $(@D)/.$(@F).0s.o $(note_file_option) -o $(@D)/.$(@F).$(base).1 &&) :
-       efi/mkreloc $(foreach base,$(VIRT_BASE) $(ALT_BASE),$(@D)/.$(@F).$(base).1) >$(@D)/.$(@F).1r.S
+       $(MKRELOC) $(foreach base,$(VIRT_BASE) $(ALT_BASE),$(@D)/.$(@F).$(base).1) >$(@D)/.$(@F).1r.S
        $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).1 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort >$(@D)/.$(@F).1s.S
        $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o

diff --git a/xen/arch/x86/efi/check.c b/xen/arch/x86/efi/check.c
index 7fedd5a6105b891938c32c2befbecfda16b19ec0..9e473faad3c9904c3ca721df46a42a78c0116d4d 100644 (file)
--- a/xen/arch/x86/efi/check.c
+++ b/xen/arch/x86/efi/check.c
@@ -2,3 +2,17 @@ int __attribute__((__ms_abi__)) test(int i)
 {
     return i;
 }
+
+/*
+ * Populate an array with "addresses" of relocatable and absolute values.
+ * This is to probe ld for (a) emitting base relocations at all and (b) not
+ * emitting base relocations for absolute symbols.
+ */
+extern const unsigned char __image_base__[], __file_alignment__[],
+                           __section_alignment__[];
+const void *const data[] = {
+    __image_base__,
+    __file_alignment__,
+    __section_alignment__,
+    data,
+};

diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 2541ba1f320a0f1a7073cf6f0bffeb8fedf167d2..fb217031ff0e342efa6eecfbb3c2a06e19c1a2fa 100644 (file)
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -86,10 +86,12 @@ static void __init efi_arch_relocate_image(unsigned long delta)
                 }
                 break;
             case PE_BASE_RELOC_DIR64:
-                if ( in_page_tables(addr) )
-                    blexit(L"Unexpected relocation type");
                 if ( delta )
+                {
                     *(u64 *)addr += delta;
+                    if ( in_page_tables(addr) )
+                        *(u64 *)addr += xen_phys_start;
+                }
                 break;
             default:
                 blexit(L"Unsupported relocation type");