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