Commit 79db4d22 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'clang-lto-v5.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux 

Pull clang LTO updates from Kees Cook:
 "Clang Link Time Optimization.

  This is built on the work done preparing for LTO by arm64 folks,
  tracing folks, etc. This includes the core changes as well as the
  remaining pieces for arm64 (LTO has been the default build method on
  Android for about 3 years now, as it is the prerequisite for the
  Control Flow Integrity protections).

  While x86 LTO enablement is done, it depends on some pending objtool
  clean-ups. It's possible that I'll send a "part 2" pull request for
  LTO that includes x86 support.

  For merge log posterity, and as detailed in commit dc5723b0
  ("kbuild: add support for Clang LTO"), here is the lt;dr to do an LTO
  build:

        make LLVM=1 LLVM_IAS=1 defconfig
        scripts/config -e LTO_CLANG_THIN
        make LLVM=1 LLVM_IAS=1

  (To do a cross-compile of arm64, add "CROSS_COMPILE=aarch64-linux-gnu-"
  and "ARCH=arm64" to the "make" command lines.)

  Summary:

   - Clang LTO build infrastructure and arm64-specific enablement (Sami
     Tolvanen)

   - Recursive build CC_FLAGS_LTO fix (Alexander Lobakin)"

* tag 'clang-lto-v5.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  kbuild: prevent CC_FLAGS_LTO self-bloating on recursive rebuilds
  arm64: allow LTO to be selected
  arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS
  arm64: vdso: disable LTO
  drivers/misc/lkdtm: disable LTO for rodata.o
  efi/libstub: disable LTO
  scripts/mod: disable LTO for empty.c
  modpost: lto: strip .lto from module names
  PCI: Fix PREL32 relocations for LTO
  init: lto: fix PREL32 relocations
  init: lto: ensure initcall ordering
  kbuild: lto: add a default list of used symbols
  kbuild: lto: merge module sections
  kbuild: lto: limit inlining
  kbuild: lto: fix module versioning
  kbuild: add support for Clang LTO
  tracing: move function tracer options to Kconfig
parents 3b9cdafb 2b868952

.gitignore

+1 −0
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ 
*.so.dbg

*.su

*.symtypes

*.symversions

*.tab.[ch]

*.tar

*.xz

Makefile

+30 −15
Original line number Diff line number Diff line
@@ -853,12 +853,8 @@ KBUILD_CFLAGS += $(DEBUG_CFLAGS) 
export DEBUG_CFLAGS



ifdef CONFIG_FUNCTION_TRACER

ifdef CONFIG_FTRACE_MCOUNT_RECORD

  # gcc 5 supports generating the mcount tables directly

  ifeq ($(call cc-option-yn,-mrecord-mcount),y)

ifdef CONFIG_FTRACE_MCOUNT_USE_CC

  CC_FLAGS_FTRACE	+= -mrecord-mcount

    export CC_USING_RECORD_MCOUNT := 1

  endif

  ifdef CONFIG_HAVE_NOP_MCOUNT

    ifeq ($(call cc-option-yn, -mnop-mcount),y)

      CC_FLAGS_FTRACE	+= -mnop-mcount
@@ -866,6 +862,12 @@ ifdef CONFIG_FTRACE_MCOUNT_RECORD 
    endif

  endif

endif

ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT

  ifdef CONFIG_HAVE_C_RECORDMCOUNT

    BUILD_C_RECORDMCOUNT := y

    export BUILD_C_RECORDMCOUNT

  endif

endif

ifdef CONFIG_HAVE_FENTRY

  ifeq ($(call cc-option-yn, -mfentry),y)

    CC_FLAGS_FTRACE	+= -mfentry
@@ -875,12 +877,6 @@ endif 
export CC_FLAGS_FTRACE

KBUILD_CFLAGS	+= $(CC_FLAGS_FTRACE) $(CC_FLAGS_USING)

KBUILD_AFLAGS	+= $(CC_FLAGS_USING)

ifdef CONFIG_DYNAMIC_FTRACE

	ifdef CONFIG_HAVE_C_RECORDMCOUNT

		BUILD_C_RECORDMCOUNT := y

		export BUILD_C_RECORDMCOUNT

	endif

endif

endif



# We trigger additional mismatches with less inlining
@@ -899,6 +895,24 @@ KBUILD_CFLAGS += $(CC_FLAGS_SCS) 
export CC_FLAGS_SCS

endif



ifdef CONFIG_LTO_CLANG

ifdef CONFIG_LTO_CLANG_THIN

CC_FLAGS_LTO	:= -flto=thin -fsplit-lto-unit

KBUILD_LDFLAGS	+= --thinlto-cache-dir=$(extmod-prefix).thinlto-cache

else

CC_FLAGS_LTO	:= -flto

endif

CC_FLAGS_LTO	+= -fvisibility=hidden



# Limit inlining across translation units to reduce binary size

KBUILD_LDFLAGS += -mllvm -import-instr-limit=5

endif



ifdef CONFIG_LTO

KBUILD_CFLAGS	+= $(CC_FLAGS_LTO)

export CC_FLAGS_LTO

endif



ifdef CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_32B

KBUILD_CFLAGS += -falign-functions=32

endif
@@ -1493,7 +1507,7 @@ MRPROPER_FILES += include/config include/generated \ 
		  *.spec



# Directories & files removed with 'make distclean'

DISTCLEAN_FILES += tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS

DISTCLEAN_FILES += tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS .thinlto-cache



# clean - Delete most, but leave enough to build external modules

#
@@ -1739,7 +1753,7 @@ PHONY += compile_commands.json 


clean-dirs := $(KBUILD_EXTMOD)

clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers $(KBUILD_EXTMOD)/modules.nsdeps \

	$(KBUILD_EXTMOD)/compile_commands.json

	$(KBUILD_EXTMOD)/compile_commands.json $(KBUILD_EXTMOD)/.thinlto-cache



PHONY += help

help:
@@ -1836,7 +1850,8 @@ clean: $(clean-dirs) 
		-o -name '.tmp_*.o.*' \

		-o -name '*.c.[012]*.*' \

		-o -name '*.ll' \

		-o -name '*.gcno' \) -type f -print | xargs rm -f

		-o -name '*.gcno' \

		-o -name '*.*.symversions' \) -type f -print | xargs rm -f



# Generate tags for editors

# ---------------------------------------------------------------------------

arch/Kconfig

+90 −0
Original line number Diff line number Diff line
@@ -603,6 +603,96 @@ config SHADOW_CALL_STACK 
	  reading and writing arbitrary memory may be able to locate them

	  and hijack control flow by modifying the stacks.



config LTO

	bool

	help

	  Selected if the kernel will be built using the compiler's LTO feature.



config LTO_CLANG

	bool

	select LTO

	help

	  Selected if the kernel will be built using Clang's LTO feature.



config ARCH_SUPPORTS_LTO_CLANG

	bool

	help

	  An architecture should select this option if it supports:

	  - compiling with Clang,

	  - compiling inline assembly with Clang's integrated assembler,

	  - and linking with LLD.



config ARCH_SUPPORTS_LTO_CLANG_THIN

	bool

	help

	  An architecture should select this option if it can support Clang's

	  ThinLTO mode.



config HAS_LTO_CLANG

	def_bool y

	# Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510

	depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD

	depends on $(success,test $(LLVM) -eq 1)

	depends on $(success,test $(LLVM_IAS) -eq 1)

	depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)

	depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)

	depends on ARCH_SUPPORTS_LTO_CLANG

	depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT

	depends on !KASAN

	depends on !GCOV_KERNEL

	help

	  The compiler and Kconfig options support building with Clang's

	  LTO.



choice

	prompt "Link Time Optimization (LTO)"

	default LTO_NONE

	help

	  This option enables Link Time Optimization (LTO), which allows the

	  compiler to optimize binaries globally.



	  If unsure, select LTO_NONE. Note that LTO is very resource-intensive

	  so it's disabled by default.



config LTO_NONE

	bool "None"

	help

	  Build the kernel normally, without Link Time Optimization (LTO).



config LTO_CLANG_FULL

	bool "Clang Full LTO (EXPERIMENTAL)"

	depends on HAS_LTO_CLANG

	depends on !COMPILE_TEST

	select LTO_CLANG

	help

          This option enables Clang's full Link Time Optimization (LTO), which

          allows the compiler to optimize the kernel globally. If you enable

          this option, the compiler generates LLVM bitcode instead of ELF

          object files, and the actual compilation from bitcode happens at

          the LTO link step, which may take several minutes depending on the

          kernel configuration. More information can be found from LLVM's

          documentation:



	    https://llvm.org/docs/LinkTimeOptimization.html



	  During link time, this option can use a large amount of RAM, and

	  may take much longer than the ThinLTO option.



config LTO_CLANG_THIN

	bool "Clang ThinLTO (EXPERIMENTAL)"

	depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN

	select LTO_CLANG

	help

	  This option enables Clang's ThinLTO, which allows for parallel

	  optimization and faster incremental compiles compared to the

	  CONFIG_LTO_CLANG_FULL option. More information can be found

	  from Clang's documentation:



	    https://clang.llvm.org/docs/ThinLTO.html



	  If unsure, say Y.

endchoice



config HAVE_ARCH_WITHIN_STACK_FRAMES

	bool

	help

arch/arm64/Kconfig

+4 −0
Original line number Diff line number Diff line
@@ -73,6 +73,8 @@ config ARM64 
	select ARCH_SUPPORTS_DEBUG_PAGEALLOC

	select ARCH_SUPPORTS_MEMORY_FAILURE

	select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK

	select ARCH_SUPPORTS_LTO_CLANG if CPU_LITTLE_ENDIAN

	select ARCH_SUPPORTS_LTO_CLANG_THIN

	select ARCH_SUPPORTS_ATOMIC_RMW

	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && (GCC_VERSION >= 50000 || CC_IS_CLANG)

	select ARCH_SUPPORTS_NUMA_BALANCING
@@ -162,6 +164,8 @@ config ARM64 
	select HAVE_DYNAMIC_FTRACE

	select HAVE_DYNAMIC_FTRACE_WITH_REGS \

		if $(cc-option,-fpatchable-function-entry=2)

	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \

		if DYNAMIC_FTRACE_WITH_REGS

	select HAVE_EFFICIENT_UNALIGNED_ACCESS

	select HAVE_FAST_GUP

	select HAVE_FTRACE_MCOUNT_RECORD

arch/arm64/kernel/vdso/Makefile

+2 −1
Original line number Diff line number Diff line
@@ -29,7 +29,8 @@ ldflags-y := -shared -nostdlib -soname=linux-vdso.so.1 --hash-style=sysv \ 
ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18

ccflags-y += -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO



CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) $(GCC_PLUGINS_CFLAGS)

CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) $(GCC_PLUGINS_CFLAGS) \

				$(CC_FLAGS_LTO)

KASAN_SANITIZE			:= n

UBSAN_SANITIZE			:= n

OBJECT_FILES_NON_STANDARD	:= y