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 $(DISABLE_STACKLEAK_PLUGIN)
22cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
23				   -fno-builtin -fpic \
24				   $(call cc-option,-mno-single-pic-base)
25
26cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
27
28KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
29				   -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \
30				   -D__NO_FORTIFY \
31				   -ffreestanding \
32				   -fno-stack-protector \
33				   $(call cc-option,-fno-addrsig) \
34				   -D__DISABLE_EXPORTS
35
36# remove SCS flags from all objects in this directory
37KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
38
39GCOV_PROFILE			:= n
40# Sanitizer runtimes are unavailable and cannot be linked here.
41KASAN_SANITIZE			:= n
42KCSAN_SANITIZE			:= n
43UBSAN_SANITIZE			:= n
44OBJECT_FILES_NON_STANDARD	:= y
45
46# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
47KCOV_INSTRUMENT			:= n
48
49lib-y				:= efi-stub-helper.o gop.o secureboot.o tpm.o \
50				   file.o mem.o random.o randomalloc.o pci.o \
51				   skip_spaces.o lib-cmdline.o lib-ctype.o \
52				   alignedmem.o relocate.o vsprintf.o
53
54# include the stub's generic dependencies from lib/ when building for ARM/arm64
55efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
56
57$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
58	$(call if_changed_rule,cc_o_c)
59
60lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o fdt.o string.o \
61				   $(patsubst %.c,lib-%.o,$(efi-deps-y))
62
63lib-$(CONFIG_ARM)		+= arm32-stub.o
64lib-$(CONFIG_ARM64)		+= arm64-stub.o
65lib-$(CONFIG_X86)		+= x86-stub.o
66CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
67CFLAGS_arm64-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
68
69#
70# For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
71# .bss section, so the .bss section of the EFI stub needs to be included in the
72# .data section of the compressed kernel to ensure initialization. Rename the
73# .bss section here so it's easy to pick out in the linker script.
74#
75STUBCOPY_FLAGS-$(CONFIG_X86)	+= --rename-section .bss=.bss.efistub,load,alloc
76STUBCOPY_RELOC-$(CONFIG_X86_32)	:= R_386_32
77STUBCOPY_RELOC-$(CONFIG_X86_64)	:= R_X86_64_64
78
79#
80# ARM discards the .data section because it disallows r/w data in the
81# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub,
82# which are preserved explicitly by the decompressor linker script.
83#
84STUBCOPY_FLAGS-$(CONFIG_ARM)	+= --rename-section .data=.data.efistub	\
85				   --rename-section .bss=.bss.efistub,load,alloc
86STUBCOPY_RELOC-$(CONFIG_ARM)	:= R_ARM_ABS
87
88#
89# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
90# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
91# So let's apply the __init annotations at the section level, by prefixing
92# the section names directly. This will ensure that even all the inline string
93# literals are covered.
94# The fact that the stub and the kernel proper are essentially the same binary
95# also means that we need to be extra careful to make sure that the stub does
96# not rely on any absolute symbol references, considering that the virtual
97# kernel mapping that the linker uses is not active yet when the stub is
98# executing. So build all C dependencies of the EFI stub into libstub, and do
99# a verification pass to see if any absolute relocations exist in any of the
100# object files.
101#
102extra-y				:= $(lib-y)
103lib-y				:= $(patsubst %.o,%.stub.o,$(lib-y))
104
105STUBCOPY_FLAGS-$(CONFIG_ARM64)	+= --prefix-alloc-sections=.init \
106				   --prefix-symbols=__efistub_
107STUBCOPY_RELOC-$(CONFIG_ARM64)	:= R_AARCH64_ABS
108
109$(obj)/%.stub.o: $(obj)/%.o FORCE
110	$(call if_changed,stubcopy)
111
112#
113# Strip debug sections and some other sections that may legally contain
114# absolute relocations, so that we can inspect the remaining sections for
115# such relocations. If none are found, regenerate the output object, but
116# this time, use objcopy and leave all sections in place.
117#
118quiet_cmd_stubcopy = STUBCPY $@
119      cmd_stubcopy =							\
120	$(STRIP) --strip-debug -o $@ $<;				\
121	if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then		\
122		echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \
123		/bin/false;						\
124	fi;								\
125	$(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@
126