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# SPDX-License-Identifier: GPL-2.0
#
# The stub may be linked into the kernel proper or into a separate boot binary,
# but in either case, it executes before the kernel does (with MMU disabled) so
# things like ftrace and stack-protector are likely to cause trouble if left
# enabled, even if doing so doesn't break the build.
#
cflags-$(CONFIG_X86_32) := -march=i386
cflags-$(CONFIG_X86_64) := -mcmodel=small
cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ \
-fPIC -fno-strict-aliasing -mno-red-zone \
-mno-mmx -mno-sse -fshort-wchar \
-Wno-pointer-sign \
$(call cc-disable-warning, address-of-packed-member) \
$(call cc-disable-warning, gnu) \
-fno-asynchronous-unwind-tables \
$(CLANG_FLAGS)
# arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
# disable the stackleak plugin
cflags-$(CONFIG_ARM64) := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-fpie $(DISABLE_STACKLEAK_PLUGIN) \
$(call cc-option,-mbranch-protection=none)
cflags-$(CONFIG_ARM) := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-fno-builtin -fpic \
$(call cc-option,-mno-single-pic-base)
cflags-$(CONFIG_RISCV) := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-fpic
cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
KBUILD_CFLAGS := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
-include $(srctree)/include/linux/hidden.h \
-D__NO_FORTIFY \
-ffreestanding \
-fno-stack-protector \
$(call cc-option,-fno-addrsig) \
-D__DISABLE_EXPORTS
#
# struct randomization only makes sense for Linux internal types, which the EFI
# stub code never touches, so let's turn off struct randomization for the stub
# altogether
#
KBUILD_CFLAGS := $(filter-out $(RANDSTRUCT_CFLAGS), $(KBUILD_CFLAGS))
# remove SCS flags from all objects in this directory
KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
# disable LTO
KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))
GCOV_PROFILE := n
# Sanitizer runtimes are unavailable and cannot be linked here.
KASAN_SANITIZE := n
KCSAN_SANITIZE := n
UBSAN_SANITIZE := n
OBJECT_FILES_NON_STANDARD := y
# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
KCOV_INSTRUMENT := n
lib-y := efi-stub-helper.o gop.o secureboot.o tpm.o \
file.o mem.o random.o randomalloc.o pci.o \
skip_spaces.o lib-cmdline.o lib-ctype.o \
alignedmem.o relocate.o vsprintf.o
# include the stub's generic dependencies from lib/ when building for ARM/arm64
efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
$(call if_changed_rule,cc_o_c)
lib-$(CONFIG_EFI_GENERIC_STUB) += efi-stub.o fdt.o string.o \
$(patsubst %.c,lib-%.o,$(efi-deps-y))
lib-$(CONFIG_ARM) += arm32-stub.o
lib-$(CONFIG_ARM64) += arm64-stub.o
lib-$(CONFIG_X86) += x86-stub.o
lib-$(CONFIG_RISCV) += riscv-stub.o
CFLAGS_arm32-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
# Even when -mbranch-protection=none is set, Clang will generate a
# .note.gnu.property for code-less object files (like lib/ctype.c),
# so work around this by explicitly removing the unwanted section.
# https://bugs.llvm.org/show_bug.cgi?id=46480
STUBCOPY_FLAGS-y += --remove-section=.note.gnu.property
#
# For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
# .bss section, so the .bss section of the EFI stub needs to be included in the
# .data section of the compressed kernel to ensure initialization. Rename the
# .bss section here so it's easy to pick out in the linker script.
#
STUBCOPY_FLAGS-$(CONFIG_X86) += --rename-section .bss=.bss.efistub,load,alloc
STUBCOPY_RELOC-$(CONFIG_X86_32) := R_386_32
STUBCOPY_RELOC-$(CONFIG_X86_64) := R_X86_64_64
#
# ARM discards the .data section because it disallows r/w data in the
# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub,
# which are preserved explicitly by the decompressor linker script.
#
STUBCOPY_FLAGS-$(CONFIG_ARM) += --rename-section .data=.data.efistub \
--rename-section .bss=.bss.efistub,load,alloc
STUBCOPY_RELOC-$(CONFIG_ARM) := R_ARM_ABS
#
# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
# So let's apply the __init annotations at the section level, by prefixing
# the section names directly. This will ensure that even all the inline string
# literals are covered.
# The fact that the stub and the kernel proper are essentially the same binary
# also means that we need to be extra careful to make sure that the stub does
# not rely on any absolute symbol references, considering that the virtual
# kernel mapping that the linker uses is not active yet when the stub is
# executing. So build all C dependencies of the EFI stub into libstub, and do
# a verification pass to see if any absolute relocations exist in any of the
# object files.
#
extra-y := $(lib-y)
lib-y := $(patsubst %.o,%.stub.o,$(lib-y))
STUBCOPY_FLAGS-$(CONFIG_ARM64) += --prefix-alloc-sections=.init \
--prefix-symbols=__efistub_
STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS
# For RISC-V, we don't need anything special other than arm64. Keep all the
# symbols in .init section and make sure that no absolute symbols references
# doesn't exist.
STUBCOPY_FLAGS-$(CONFIG_RISCV) += --prefix-alloc-sections=.init \
--prefix-symbols=__efistub_
STUBCOPY_RELOC-$(CONFIG_RISCV) := R_RISCV_HI20
$(obj)/%.stub.o: $(obj)/%.o FORCE
$(call if_changed,stubcopy)
#
# Strip debug sections and some other sections that may legally contain
# absolute relocations, so that we can inspect the remaining sections for
# such relocations. If none are found, regenerate the output object, but
# this time, use objcopy and leave all sections in place.
#
quiet_cmd_stubcopy = STUBCPY $@
cmd_stubcopy = \
$(STRIP) --strip-debug -o $@ $<; \
if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then \
echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \
/bin/false; \
fi; \
$(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@
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