1# SPDX-License-Identifier: GPL-2.0 2# 3# The stub may be linked into the kernel proper or into a separate boot binary, 4# but in either case, it executes before the kernel does (with MMU disabled) so 5# things like ftrace and stack-protector are likely to cause trouble if left 6# enabled, even if doing so doesn't break the build. 7# 8cflags-$(CONFIG_X86_32) := -march=i386 9cflags-$(CONFIG_X86_64) := -mcmodel=small 10cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ \ 11 -fPIC -fno-strict-aliasing -mno-red-zone \ 12 -mno-mmx -mno-sse -fshort-wchar \ 13 -Wno-pointer-sign \ 14 $(call cc-disable-warning, address-of-packed-member) \ 15 $(call cc-disable-warning, gnu) \ 16 -fno-asynchronous-unwind-tables 17 18# arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly 19# disable the stackleak plugin 20cflags-$(CONFIG_ARM64) := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \ 21 -fpie $(DISABLE_STACKLEAK_PLUGIN) \ 22 $(call cc-option,-mbranch-protection=none) 23cflags-$(CONFIG_ARM) := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \ 24 -fno-builtin -fpic \ 25 $(call cc-option,-mno-single-pic-base) 26cflags-$(CONFIG_RISCV) := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \ 27 -fpic 28 29cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt 30 31KBUILD_CFLAGS := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \ 32 -include $(srctree)/include/linux/hidden.h \ 33 -D__NO_FORTIFY \ 34 -ffreestanding \ 35 -fno-stack-protector \ 36 $(call cc-option,-fno-addrsig) \ 37 -D__DISABLE_EXPORTS 38 39# remove SCS flags from all objects in this directory 40KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS)) 41# disable LTO 42KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS)) 43 44GCOV_PROFILE := n 45# Sanitizer runtimes are unavailable and cannot be linked here. 46KASAN_SANITIZE := n 47KCSAN_SANITIZE := n 48UBSAN_SANITIZE := n 49OBJECT_FILES_NON_STANDARD := y 50 51# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in. 52KCOV_INSTRUMENT := n 53 54lib-y := efi-stub-helper.o gop.o secureboot.o tpm.o \ 55 file.o mem.o random.o randomalloc.o pci.o \ 56 skip_spaces.o lib-cmdline.o lib-ctype.o \ 57 alignedmem.o relocate.o vsprintf.o 58 59# include the stub's generic dependencies from lib/ when building for ARM/arm64 60efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c 61 62$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE 63 $(call if_changed_rule,cc_o_c) 64 65lib-$(CONFIG_EFI_GENERIC_STUB) += efi-stub.o fdt.o string.o \ 66 $(patsubst %.c,lib-%.o,$(efi-deps-y)) 67 68lib-$(CONFIG_ARM) += arm32-stub.o 69lib-$(CONFIG_ARM64) += arm64-stub.o 70lib-$(CONFIG_X86) += x86-stub.o 71lib-$(CONFIG_RISCV) += riscv-stub.o 72CFLAGS_arm32-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET) 73 74# Even when -mbranch-protection=none is set, Clang will generate a 75# .note.gnu.property for code-less object files (like lib/ctype.c), 76# so work around this by explicitly removing the unwanted section. 77# https://bugs.llvm.org/show_bug.cgi?id=46480 78STUBCOPY_FLAGS-y += --remove-section=.note.gnu.property 79 80# 81# For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the 82# .bss section, so the .bss section of the EFI stub needs to be included in the 83# .data section of the compressed kernel to ensure initialization. Rename the 84# .bss section here so it's easy to pick out in the linker script. 85# 86STUBCOPY_FLAGS-$(CONFIG_X86) += --rename-section .bss=.bss.efistub,load,alloc 87STUBCOPY_RELOC-$(CONFIG_X86_32) := R_386_32 88STUBCOPY_RELOC-$(CONFIG_X86_64) := R_X86_64_64 89 90# 91# ARM discards the .data section because it disallows r/w data in the 92# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub, 93# which are preserved explicitly by the decompressor linker script. 94# 95STUBCOPY_FLAGS-$(CONFIG_ARM) += --rename-section .data=.data.efistub \ 96 --rename-section .bss=.bss.efistub,load,alloc 97STUBCOPY_RELOC-$(CONFIG_ARM) := R_ARM_ABS 98 99# 100# arm64 puts the stub in the kernel proper, which will unnecessarily retain all 101# code indefinitely unless it is annotated as __init/__initdata/__initconst etc. 102# So let's apply the __init annotations at the section level, by prefixing 103# the section names directly. This will ensure that even all the inline string 104# literals are covered. 105# The fact that the stub and the kernel proper are essentially the same binary 106# also means that we need to be extra careful to make sure that the stub does 107# not rely on any absolute symbol references, considering that the virtual 108# kernel mapping that the linker uses is not active yet when the stub is 109# executing. So build all C dependencies of the EFI stub into libstub, and do 110# a verification pass to see if any absolute relocations exist in any of the 111# object files. 112# 113extra-y := $(lib-y) 114lib-y := $(patsubst %.o,%.stub.o,$(lib-y)) 115 116STUBCOPY_FLAGS-$(CONFIG_ARM64) += --prefix-alloc-sections=.init \ 117 --prefix-symbols=__efistub_ 118STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS 119 120# For RISC-V, we don't need anything special other than arm64. Keep all the 121# symbols in .init section and make sure that no absolute symbols references 122# doesn't exist. 123STUBCOPY_FLAGS-$(CONFIG_RISCV) += --prefix-alloc-sections=.init \ 124 --prefix-symbols=__efistub_ 125STUBCOPY_RELOC-$(CONFIG_RISCV) := R_RISCV_HI20 126 127$(obj)/%.stub.o: $(obj)/%.o FORCE 128 $(call if_changed,stubcopy) 129 130# 131# Strip debug sections and some other sections that may legally contain 132# absolute relocations, so that we can inspect the remaining sections for 133# such relocations. If none are found, regenerate the output object, but 134# this time, use objcopy and leave all sections in place. 135# 136quiet_cmd_stubcopy = STUBCPY $@ 137 cmd_stubcopy = \ 138 $(STRIP) --strip-debug -o $@ $<; \ 139 if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then \ 140 echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \ 141 /bin/false; \ 142 fi; \ 143 $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@ 144