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