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#
8
9# non-x86 reuses KBUILD_CFLAGS, x86 does not
10cflags-y			:= $(KBUILD_CFLAGS)
11
12cflags-$(CONFIG_X86_32)		:= -march=i386
13cflags-$(CONFIG_X86_64)		:= -mcmodel=small
14cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
15				   -fPIC -fno-strict-aliasing -mno-red-zone \
16				   -mno-mmx -mno-sse -fshort-wchar \
17				   -Wno-pointer-sign \
18				   $(call cc-disable-warning, address-of-packed-member) \
19				   $(call cc-disable-warning, gnu) \
20				   -fno-asynchronous-unwind-tables \
21				   $(CLANG_FLAGS)
22
23# arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
24# disable the stackleak plugin
25cflags-$(CONFIG_ARM64)		+= -fpie $(DISABLE_STACKLEAK_PLUGIN) \
26				   $(call cc-option,-mbranch-protection=none)
27cflags-$(CONFIG_ARM)		+= -DEFI_HAVE_STRLEN -DEFI_HAVE_STRNLEN \
28				   -fno-builtin -fpic \
29				   $(call cc-option,-mno-single-pic-base)
30cflags-$(CONFIG_RISCV)		+= -fpic
31cflags-$(CONFIG_LOONGARCH)	+= -fpie
32
33cflags-$(CONFIG_EFI_PARAMS_FROM_FDT)	+= -I$(srctree)/scripts/dtc/libfdt
34
35KBUILD_CFLAGS			:= $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
36				   -Os -DDISABLE_BRANCH_PROFILING \
37				   -include $(srctree)/include/linux/hidden.h \
38				   -D__NO_FORTIFY \
39				   -ffreestanding \
40				   -fno-stack-protector \
41				   $(call cc-option,-fno-addrsig) \
42				   -D__DISABLE_EXPORTS
43
44#
45# struct randomization only makes sense for Linux internal types, which the EFI
46# stub code never touches, so let's turn off struct randomization for the stub
47# altogether
48#
49KBUILD_CFLAGS := $(filter-out $(RANDSTRUCT_CFLAGS), $(KBUILD_CFLAGS))
50
51# remove SCS flags from all objects in this directory
52KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
53# disable CFI
54KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_CFI), $(KBUILD_CFLAGS))
55# disable LTO
56KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))
57
58GCOV_PROFILE			:= n
59# Sanitizer runtimes are unavailable and cannot be linked here.
60KASAN_SANITIZE			:= n
61KCSAN_SANITIZE			:= n
62KMSAN_SANITIZE			:= n
63UBSAN_SANITIZE			:= n
64OBJECT_FILES_NON_STANDARD	:= y
65
66# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
67KCOV_INSTRUMENT			:= n
68
69lib-y				:= efi-stub-helper.o gop.o secureboot.o tpm.o \
70				   file.o mem.o random.o randomalloc.o pci.o \
71				   skip_spaces.o lib-cmdline.o lib-ctype.o \
72				   alignedmem.o relocate.o printk.o vsprintf.o
73
74# include the stub's libfdt dependencies from lib/ when needed
75libfdt-deps			:= fdt_rw.c fdt_ro.c fdt_wip.c fdt.c \
76				   fdt_empty_tree.c fdt_sw.c
77
78lib-$(CONFIG_EFI_PARAMS_FROM_FDT) += fdt.o \
79				     $(patsubst %.c,lib-%.o,$(libfdt-deps))
80
81$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
82	$(call if_changed_rule,cc_o_c)
83
84lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o string.o intrinsics.o systable.o
85
86lib-$(CONFIG_ARM)		+= arm32-stub.o
87lib-$(CONFIG_ARM64)		+= arm64-stub.o arm64-entry.o
88lib-$(CONFIG_X86)		+= x86-stub.o
89lib-$(CONFIG_RISCV)		+= riscv-stub.o
90lib-$(CONFIG_LOONGARCH)		+= loongarch-stub.o
91
92CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
93
94zboot-obj-$(CONFIG_RISCV)	:= lib-clz_ctz.o lib-ashldi3.o
95lib-$(CONFIG_EFI_ZBOOT)		+= zboot.o $(zboot-obj-y)
96
97extra-y				:= $(lib-y)
98lib-y				:= $(patsubst %.o,%.stub.o,$(lib-y))
99
100# Even when -mbranch-protection=none is set, Clang will generate a
101# .note.gnu.property for code-less object files (like lib/ctype.c),
102# so work around this by explicitly removing the unwanted section.
103# https://bugs.llvm.org/show_bug.cgi?id=46480
104STUBCOPY_FLAGS-y		+= --remove-section=.note.gnu.property
105
106#
107# For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
108# .bss section, so the .bss section of the EFI stub needs to be included in the
109# .data section of the compressed kernel to ensure initialization. Rename the
110# .bss section here so it's easy to pick out in the linker script.
111#
112STUBCOPY_FLAGS-$(CONFIG_X86)	+= --rename-section .bss=.bss.efistub,load,alloc
113STUBCOPY_RELOC-$(CONFIG_X86_32)	:= R_386_32
114STUBCOPY_RELOC-$(CONFIG_X86_64)	:= R_X86_64_64
115
116#
117# ARM discards the .data section because it disallows r/w data in the
118# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub,
119# which are preserved explicitly by the decompressor linker script.
120#
121STUBCOPY_FLAGS-$(CONFIG_ARM)	+= --rename-section .data=.data.efistub	\
122				   --rename-section .bss=.bss.efistub,load,alloc
123STUBCOPY_RELOC-$(CONFIG_ARM)	:= R_ARM_ABS
124
125#
126# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
127# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
128# So let's apply the __init annotations at the section level, by prefixing
129# the section names directly. This will ensure that even all the inline string
130# literals are covered.
131# The fact that the stub and the kernel proper are essentially the same binary
132# also means that we need to be extra careful to make sure that the stub does
133# not rely on any absolute symbol references, considering that the virtual
134# kernel mapping that the linker uses is not active yet when the stub is
135# executing. So build all C dependencies of the EFI stub into libstub, and do
136# a verification pass to see if any absolute relocations exist in any of the
137# object files.
138#
139STUBCOPY_FLAGS-$(CONFIG_ARM64)	+= --prefix-alloc-sections=.init \
140				   --prefix-symbols=__efistub_
141STUBCOPY_RELOC-$(CONFIG_ARM64)	:= R_AARCH64_ABS64
142
143# For RISC-V, we don't need anything special other than arm64. Keep all the
144# symbols in .init section and make sure that no absolute symbols references
145# doesn't exist.
146STUBCOPY_FLAGS-$(CONFIG_RISCV)	+= --prefix-alloc-sections=.init \
147				   --prefix-symbols=__efistub_
148STUBCOPY_RELOC-$(CONFIG_RISCV)	:= R_RISCV_HI20
149
150# For LoongArch, keep all the symbols in .init section and make sure that no
151# absolute symbols references exist.
152STUBCOPY_FLAGS-$(CONFIG_LOONGARCH)	+= --prefix-alloc-sections=.init \
153					   --prefix-symbols=__efistub_
154STUBCOPY_RELOC-$(CONFIG_LOONGARCH)	:= R_LARCH_MARK_LA
155
156$(obj)/%.stub.o: $(obj)/%.o FORCE
157	$(call if_changed,stubcopy)
158
159#
160# Strip debug sections and some other sections that may legally contain
161# absolute relocations, so that we can inspect the remaining sections for
162# such relocations. If none are found, regenerate the output object, but
163# this time, use objcopy and leave all sections in place.
164#
165quiet_cmd_stubcopy = STUBCPY $@
166      cmd_stubcopy =							\
167	$(STRIP) --strip-debug -o $@ $<;				\
168	if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then		\
169		echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \
170		/bin/false;						\
171	fi;								\
172	$(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@
173