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
29cflags-$(CONFIG_LOONGARCH)	:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
30				   -fpie
31
32cflags-$(CONFIG_EFI_PARAMS_FROM_FDT)	+= -I$(srctree)/scripts/dtc/libfdt
33
34KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
35				   -include $(srctree)/include/linux/hidden.h \
36				   -D__NO_FORTIFY \
37				   -ffreestanding \
38				   -fno-stack-protector \
39				   $(call cc-option,-fno-addrsig) \
40				   -D__DISABLE_EXPORTS
41
42#
43# struct randomization only makes sense for Linux internal types, which the EFI
44# stub code never touches, so let's turn off struct randomization for the stub
45# altogether
46#
47KBUILD_CFLAGS := $(filter-out $(RANDSTRUCT_CFLAGS), $(KBUILD_CFLAGS))
48
49# remove SCS flags from all objects in this directory
50KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
51# disable CFI
52KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_CFI), $(KBUILD_CFLAGS))
53# disable LTO
54KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))
55
56GCOV_PROFILE			:= n
57# Sanitizer runtimes are unavailable and cannot be linked here.
58KASAN_SANITIZE			:= n
59KCSAN_SANITIZE			:= n
60KMSAN_SANITIZE			:= n
61UBSAN_SANITIZE			:= n
62OBJECT_FILES_NON_STANDARD	:= y
63
64# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
65KCOV_INSTRUMENT			:= n
66
67lib-y				:= efi-stub-helper.o gop.o secureboot.o tpm.o \
68				   file.o mem.o random.o randomalloc.o pci.o \
69				   skip_spaces.o lib-cmdline.o lib-ctype.o \
70				   alignedmem.o relocate.o vsprintf.o
71
72# include the stub's libfdt dependencies from lib/ when needed
73libfdt-deps			:= fdt_rw.c fdt_ro.c fdt_wip.c fdt.c \
74				   fdt_empty_tree.c fdt_sw.c
75
76lib-$(CONFIG_EFI_PARAMS_FROM_FDT) += fdt.o \
77				     $(patsubst %.c,lib-%.o,$(libfdt-deps))
78
79$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
80	$(call if_changed_rule,cc_o_c)
81
82lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o string.o intrinsics.o systable.o
83
84lib-$(CONFIG_ARM)		+= arm32-stub.o
85lib-$(CONFIG_ARM64)		+= arm64-stub.o
86lib-$(CONFIG_X86)		+= x86-stub.o
87lib-$(CONFIG_RISCV)		+= riscv-stub.o
88lib-$(CONFIG_LOONGARCH)		+= loongarch-stub.o
89
90CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
91
92zboot-obj-$(CONFIG_RISCV)	:= lib-clz_ctz.o lib-ashldi3.o
93lib-$(CONFIG_EFI_ZBOOT)		+= zboot.o $(zboot-obj-y)
94
95extra-y				:= $(lib-y)
96lib-y				:= $(patsubst %.o,%.stub.o,$(lib-y))
97
98# Even when -mbranch-protection=none is set, Clang will generate a
99# .note.gnu.property for code-less object files (like lib/ctype.c),
100# so work around this by explicitly removing the unwanted section.
101# https://bugs.llvm.org/show_bug.cgi?id=46480
102STUBCOPY_FLAGS-y		+= --remove-section=.note.gnu.property
103
104#
105# For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
106# .bss section, so the .bss section of the EFI stub needs to be included in the
107# .data section of the compressed kernel to ensure initialization. Rename the
108# .bss section here so it's easy to pick out in the linker script.
109#
110STUBCOPY_FLAGS-$(CONFIG_X86)	+= --rename-section .bss=.bss.efistub,load,alloc
111STUBCOPY_RELOC-$(CONFIG_X86_32)	:= R_386_32
112STUBCOPY_RELOC-$(CONFIG_X86_64)	:= R_X86_64_64
113
114#
115# ARM discards the .data section because it disallows r/w data in the
116# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub,
117# which are preserved explicitly by the decompressor linker script.
118#
119STUBCOPY_FLAGS-$(CONFIG_ARM)	+= --rename-section .data=.data.efistub	\
120				   --rename-section .bss=.bss.efistub,load,alloc
121STUBCOPY_RELOC-$(CONFIG_ARM)	:= R_ARM_ABS
122
123#
124# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
125# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
126# So let's apply the __init annotations at the section level, by prefixing
127# the section names directly. This will ensure that even all the inline string
128# literals are covered.
129# The fact that the stub and the kernel proper are essentially the same binary
130# also means that we need to be extra careful to make sure that the stub does
131# not rely on any absolute symbol references, considering that the virtual
132# kernel mapping that the linker uses is not active yet when the stub is
133# executing. So build all C dependencies of the EFI stub into libstub, and do
134# a verification pass to see if any absolute relocations exist in any of the
135# object files.
136#
137STUBCOPY_FLAGS-$(CONFIG_ARM64)	+= --prefix-alloc-sections=.init \
138				   --prefix-symbols=__efistub_
139STUBCOPY_RELOC-$(CONFIG_ARM64)	:= R_AARCH64_ABS
140
141# For RISC-V, we don't need anything special other than arm64. Keep all the
142# symbols in .init section and make sure that no absolute symbols references
143# doesn't exist.
144STUBCOPY_FLAGS-$(CONFIG_RISCV)	+= --prefix-alloc-sections=.init \
145				   --prefix-symbols=__efistub_
146STUBCOPY_RELOC-$(CONFIG_RISCV)	:= R_RISCV_HI20
147
148# For LoongArch, keep all the symbols in .init section and make sure that no
149# absolute symbols references exist.
150STUBCOPY_FLAGS-$(CONFIG_LOONGARCH)	+= --prefix-alloc-sections=.init \
151					   --prefix-symbols=__efistub_
152STUBCOPY_RELOC-$(CONFIG_LOONGARCH)	:= R_LARCH_MARK_LA
153
154$(obj)/%.stub.o: $(obj)/%.o FORCE
155	$(call if_changed,stubcopy)
156
157#
158# Strip debug sections and some other sections that may legally contain
159# absolute relocations, so that we can inspect the remaining sections for
160# such relocations. If none are found, regenerate the output object, but
161# this time, use objcopy and leave all sections in place.
162#
163quiet_cmd_stubcopy = STUBCPY $@
164      cmd_stubcopy =							\
165	$(STRIP) --strip-debug -o $@ $<;				\
166	if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then		\
167		echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \
168		/bin/false;						\
169	fi;								\
170	$(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@
171