diff -drupN a/Makefile b/Makefile
--- a/Makefile	2018-08-06 17:23:04.000000000 +0300
+++ b/Makefile	2022-06-12 05:28:14.000000000 +0300
@@ -303,7 +303,7 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH"
 
 HOSTCC       = gcc
 HOSTCXX      = g++
-HOSTCFLAGS   = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu89
+HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu89
 HOSTCXXFLAGS = -O2
 
 ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
@@ -348,6 +348,7 @@ include scripts/Kbuild.include
 # Make variables (CC, etc...)
 AS		= $(CROSS_COMPILE)as
 LD		= $(CROSS_COMPILE)ld
+LDGOLD		= $(CROSS_COMPILE)ld.gold
 CC		= $(CROSS_COMPILE)gcc
 CPP		= $(CC) -E
 AR		= $(CROSS_COMPILE)ar
@@ -623,6 +624,20 @@ CFLAGS_GCOV	:= -fprofile-arcs -ftest-cov
 CFLAGS_KCOV	:= $(call cc-option,-fsanitize-coverage=trace-pc,)
 export CFLAGS_GCOV CFLAGS_KCOV
 
+# Make toolchain changes before including arch/$(SRCARCH)/Makefile to ensure
+# ar/cc/ld-* macros return correct values.
+ifdef CONFIG_LTO_CLANG
+# use GNU gold with LLVMgold for LTO linking, and LD for vmlinux_link
+LDFINAL_vmlinux := $(LD)
+LD		:= $(LDGOLD)
+LDFLAGS		+= -plugin LLVMgold.so
+# use llvm-ar for building symbol tables from IR files, and llvm-dis instead
+# of objdump for processing symbol versions and exports
+LLVM_AR		:= llvm-ar
+LLVM_DIS	:= llvm-dis
+export LLVM_AR LLVM_DIS
+endif
+
 # The arch Makefile can set ARCH_{CPP,A,C}FLAGS to override the default
 # values of the respective KBUILD_* variables
 ARCH_CPPFLAGS :=
@@ -642,8 +657,56 @@ KBUILD_CFLAGS	+= $(call cc-option,-ffunc
 KBUILD_CFLAGS	+= $(call cc-option,-fdata-sections,)
 endif
 
+ifdef CONFIG_LTO_CLANG
+lto-clang-flags	:= -flto -fvisibility=hidden
+
+# allow disabling only clang LTO where needed
+DISABLE_LTO_CLANG := -fno-lto -fvisibility=default
+export DISABLE_LTO_CLANG
+endif
+
+ifdef CONFIG_LTO
+lto-flags	:= $(lto-clang-flags)
+KBUILD_CFLAGS	+= $(lto-flags)
+
+DISABLE_LTO	:= $(DISABLE_LTO_CLANG)
+export DISABLE_LTO
+
+# LDFINAL_vmlinux and LDFLAGS_FINAL_vmlinux can be set to override
+# the linker and flags for vmlinux_link.
+export LDFINAL_vmlinux LDFLAGS_FINAL_vmlinux
+endif
+
+ifdef CONFIG_CFI_CLANG
+cfi-clang-flags	+= -fsanitize=cfi
+DISABLE_CFI_CLANG := -fno-sanitize=cfi
+ifdef CONFIG_MODULES
+cfi-clang-flags	+= -fsanitize-cfi-cross-dso
+DISABLE_CFI_CLANG += -fno-sanitize-cfi-cross-dso
+endif
+ifdef CONFIG_CFI_PERMISSIVE
+cfi-clang-flags	+= -fsanitize-recover=cfi -fno-sanitize-trap=cfi
+endif
+
+# also disable CFI when LTO is disabled
+DISABLE_LTO_CLANG += $(DISABLE_CFI_CLANG)
+# allow disabling only clang CFI where needed
+export DISABLE_CFI_CLANG
+endif
+
+ifdef CONFIG_CFI
+# cfi-flags are re-tested in prepare-compiler-check
+cfi-flags	:= $(cfi-clang-flags)
+KBUILD_CFLAGS	+= $(cfi-flags)
+
+DISABLE_CFI	:= $(DISABLE_CFI_CLANG)
+DISABLE_LTO	+= $(DISABLE_CFI)
+export DISABLE_CFI
+endif
+
 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
-KBUILD_CFLAGS	+= -Os $(call cc-disable-warning,maybe-uninitialized,)
+KBUILD_CFLAGS	+= $(call cc-option,-Oz,-Os)
+KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
 else
 ifdef CONFIG_PROFILE_ALL_BRANCHES
 KBUILD_CFLAGS	+= -O2 $(call cc-disable-warning,maybe-uninitialized,)
@@ -703,11 +766,22 @@ endif
 KBUILD_CFLAGS += $(stackp-flag)
 
 ifeq ($(cc-name),clang)
+ifneq ($(CROSS_COMPILE),)
+CLANG_TRIPLE    ?= $(CROSS_COMPILE)
+CLANG_TARGET	:= --target=$(notdir $(CLANG_TRIPLE:%-=%))
+GCC_TOOLCHAIN	:= $(realpath $(dir $(shell which $(LD)))/..)
+endif
+ifneq ($(GCC_TOOLCHAIN),)
+CLANG_GCC_TC	:= --gcc-toolchain=$(GCC_TOOLCHAIN)
+endif
+KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
+KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
 KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
-KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable)
 KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
 KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
+KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
+KBUILD_CFLAGS += $(call cc-disable-warning, duplicate-decl-specifier)
 # Quiet clang warning: comparison of unsigned expression < 0 is always false
 KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
 # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
@@ -715,6 +789,8 @@ KBUILD_CFLAGS += $(call cc-disable-warni
 # See modpost pattern 2
 KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
 KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
+KBUILD_CFLAGS += $(call cc-option, -no-integrated-as)
+KBUILD_AFLAGS += $(call cc-option, -no-integrated-as)
 else
 
 # These warnings generated too much noise in a regular build.
@@ -1079,6 +1155,22 @@ prepare-objtool: $(objtool_target)
 # CC_STACKPROTECTOR_STRONG! Why did it build with _REGULAR?!")
 PHONY += prepare-compiler-check
 prepare-compiler-check: FORCE
+# Make sure we're using a supported toolchain with LTO_CLANG
+ifdef CONFIG_LTO_CLANG
+  ifneq ($(call clang-ifversion, -ge, 0500, y), y)
+	@echo Cannot use CONFIG_LTO_CLANG: requires clang 5.0 or later >&2 && exit 1
+  endif
+  ifneq ($(call gold-ifversion, -ge, 112000000, y), y)
+	@echo Cannot use CONFIG_LTO_CLANG: requires GNU gold 1.12 or later >&2 && exit 1
+  endif
+endif
+# Make sure compiler supports LTO flags
+ifdef lto-flags
+  ifeq ($(call cc-option, $(lto-flags)),)
+	@echo Cannot use CONFIG_LTO: $(lto-flags) not supported by compiler \
+		>&2 && exit 1
+  endif
+endif
 # Make sure compiler supports requested stack protector flag.
 ifdef stackp-name
   ifeq ($(call cc-option, $(stackp-flag)),)
@@ -1093,6 +1185,11 @@ ifdef stackp-check
                   $(stackp-flag) available but compiler is broken >&2 && exit 1
   endif
 endif
+ifdef cfi-flags
+  ifeq ($(call cc-option, $(cfi-flags)),)
+	@echo Cannot use CONFIG_CFI: $(cfi-flags) not supported by compiler >&2 && exit 1
+  endif
+endif
 	@:
 
 # Generate some files
@@ -1378,6 +1475,8 @@ help:
 	@echo  '                    (default: $$(INSTALL_MOD_PATH)/lib/firmware)'
 	@echo  '  dir/            - Build all files in dir and below'
 	@echo  '  dir/file.[ois]  - Build specified target only'
+	@echo  '  dir/file.ll     - Build the LLVM assembly file'
+	@echo  '                    (requires compiler support for LLVM assembly generation)'
 	@echo  '  dir/file.lst    - Build specified mixed source/assembly target only'
 	@echo  '                    (requires a recent binutils and recent build (System.map))'
 	@echo  '  dir/file.ko     - Build module including final link'
@@ -1562,7 +1661,9 @@ clean: $(clean-dirs)
 		-o -name '*.symtypes' -o -name 'modules.order' \
 		-o -name modules.builtin -o -name '.tmp_*.o.*' \
 		-o -name '*.c.[012]*.*' \
-		-o -name '*.gcno' \) -type f -print | xargs rm -f
+		-o -name '*.ll' \
+		-o -name '*.gcno' \
+		-o -name '*.*.symversions' \) -type f -print | xargs rm -f
 
 # Generate tags for editors
 # ---------------------------------------------------------------------------
@@ -1665,6 +1766,8 @@ endif
 	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
 %.symtypes: %.c prepare scripts FORCE
 	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
+%.ll: %.c prepare scripts FORCE
+	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
 
 # Modules
 /: prepare scripts FORCE