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 \
10				   $(call cc-option,-maccumulate-outgoing-args)
11cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
12				   -fPIC -fno-strict-aliasing -mno-red-zone \
13				   -mno-mmx -mno-sse -fshort-wchar \
14				   -Wno-pointer-sign \
15				   $(call cc-disable-warning, address-of-packed-member) \
16				   $(call cc-disable-warning, gnu) \
17				   -fno-asynchronous-unwind-tables
18
19# arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
20# disable the stackleak plugin
21cflags-$(CONFIG_ARM64)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
22				   -fpie $(DISABLE_STACKLEAK_PLUGIN)
23cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
24				   -fno-builtin -fpic \
25				   $(call cc-option,-mno-single-pic-base)
26
27cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
28
29KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
30				   -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \
31				   -D__NO_FORTIFY \
32				   -ffreestanding \
33				   -fno-stack-protector \
34				   $(call cc-option,-fno-addrsig) \
35				   -D__DISABLE_EXPORTS
36
37# remove SCS flags from all objects in this directory
38KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
39
40GCOV_PROFILE			:= n
41# Sanitizer runtimes are unavailable and cannot be linked here.
42KASAN_SANITIZE			:= n
43KCSAN_SANITIZE			:= n
44UBSAN_SANITIZE			:= n
45OBJECT_FILES_NON_STANDARD	:= y
46
47# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
48KCOV_INSTRUMENT			:= n
49
50lib-y				:= efi-stub-helper.o gop.o secureboot.o tpm.o \
51				   file.o mem.o random.o randomalloc.o pci.o \
52				   skip_spaces.o lib-cmdline.o lib-ctype.o \
53				   alignedmem.o relocate.o vsprintf.o
54
55# include the stub's generic dependencies from lib/ when building for ARM/arm64
56efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
57
58$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
59	$(call if_changed_rule,cc_o_c)
60
61lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o fdt.o string.o \
62				   $(patsubst %.c,lib-%.o,$(efi-deps-y))
63
64lib-$(CONFIG_ARM)		+= arm32-stub.o
65lib-$(CONFIG_ARM64)		+= arm64-stub.o
66lib-$(CONFIG_X86)		+= x86-stub.o
67CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
68CFLAGS_arm64-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
69
70#
71# For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
72# .bss section, so the .bss section of the EFI stub needs to be included in the
73# .data section of the compressed kernel to ensure initialization. Rename the
74# .bss section here so it's easy to pick out in the linker script.
75#
76STUBCOPY_FLAGS-$(CONFIG_X86)	+= --rename-section .bss=.bss.efistub,load,alloc
77STUBCOPY_RELOC-$(CONFIG_X86_32)	:= R_386_32
78STUBCOPY_RELOC-$(CONFIG_X86_64)	:= R_X86_64_64
79
80#
81# ARM discards the .data section because it disallows r/w data in the
82# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub,
83# which are preserved explicitly by the decompressor linker script.
84#
85STUBCOPY_FLAGS-$(CONFIG_ARM)	+= --rename-section .data=.data.efistub	\
86				   --rename-section .bss=.bss.efistub,load,alloc
87STUBCOPY_RELOC-$(CONFIG_ARM)	:= R_ARM_ABS
88
89#
90# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
91# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
92# So let's apply the __init annotations at the section level, by prefixing
93# the section names directly. This will ensure that even all the inline string
94# literals are covered.
95# The fact that the stub and the kernel proper are essentially the same binary
96# also means that we need to be extra careful to make sure that the stub does
97# not rely on any absolute symbol references, considering that the virtual
98# kernel mapping that the linker uses is not active yet when the stub is
99# executing. So build all C dependencies of the EFI stub into libstub, and do
100# a verification pass to see if any absolute relocations exist in any of the
101# object files.
102#
103extra-y				:= $(lib-y)
104lib-y				:= $(patsubst %.o,%.stub.o,$(lib-y))
105
106STUBCOPY_FLAGS-$(CONFIG_ARM64)	+= --prefix-alloc-sections=.init \
107				   --prefix-symbols=__efistub_
108STUBCOPY_RELOC-$(CONFIG_ARM64)	:= R_AARCH64_ABS
109
110$(obj)/%.stub.o: $(obj)/%.o FORCE
111	$(call if_changed,stubcopy)
112
113#
114# Strip debug sections and some other sections that may legally contain
115# absolute relocations, so that we can inspect the remaining sections for
116# such relocations. If none are found, regenerate the output object, but
117# this time, use objcopy and leave all sections in place.
118#
119quiet_cmd_stubcopy = STUBCPY $@
120      cmd_stubcopy =							\
121	$(STRIP) --strip-debug -o $@ $<;				\
122	if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then		\
123		echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \
124		/bin/false;						\
125	fi;								\
126	$(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@
127