Commit b1a1a1a0 authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Kees Cook
Browse files

kbuild: lto: postpone objtool 



With LTO, LLVM bitcode won't be compiled into native code until
modpost_link, or modfinal for modules. This change postpones calls
to objtool until after these steps, and moves objtool_args to
Makefile.lib, so the arguments can be reused in Makefile.modfinal.

As we didn't have objects to process earlier, we use --duplicate
when processing vmlinux.o. This change also disables unreachable
instruction warnings with LTO to avoid warnings about the int3
padding between functions.

Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
parent 41425ebe

scripts/Makefile.build

+2 −20
Original line number Diff line number Diff line
@@ -218,30 +218,11 @@ cmd_record_mcount = $(if $(findstring $(strip $(CC_FLAGS_FTRACE)),$(_c_flags)), 
endif # CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT



ifdef CONFIG_STACK_VALIDATION

ifndef CONFIG_LTO_CLANG

ifneq ($(SKIP_STACK_VALIDATION),1)



__objtool_obj := $(objtree)/tools/objtool/objtool



objtool_args = $(if $(CONFIG_UNWINDER_ORC),orc generate,check)



objtool_args += $(if $(part-of-module), --module,)



ifndef CONFIG_FRAME_POINTER

objtool_args += --no-fp

endif

ifdef CONFIG_GCOV_KERNEL

objtool_args += --no-unreachable

endif

ifdef CONFIG_RETPOLINE

  objtool_args += --retpoline

endif

ifdef CONFIG_X86_SMAP

  objtool_args += --uaccess

endif

ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL

  objtool_args += --mcount

endif



# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory

# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file

# 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
@@ -253,6 +234,7 @@ objtool_obj = $(if $(patsubst y%,, \ 
	$(__objtool_obj))



endif # SKIP_STACK_VALIDATION

endif # CONFIG_LTO_CLANG

endif # CONFIG_STACK_VALIDATION



# Rebuild all objects when objtool changes, or is enabled/disabled.

scripts/Makefile.lib

+12 −0
Original line number Diff line number Diff line
@@ -220,6 +220,18 @@ dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc \ 
		 $(addprefix -I,$(DTC_INCLUDE))                          \

		 -undef -D__DTS__



# Objtool arguments are also needed for modfinal with LTO, so we define

# then here to avoid duplication.

objtool_args =								\

	$(if $(CONFIG_UNWINDER_ORC),orc generate,check)			\

	$(if $(part-of-module), --module,)				\

	$(if $(CONFIG_FRAME_POINTER),, --no-fp)				\

	$(if $(or $(CONFIG_GCOV_KERNEL),$(CONFIG_LTO_CLANG)), 		\

		--no-unreachable,)					\

	$(if $(CONFIG_RETPOLINE), --retpoline,)				\

	$(if $(CONFIG_X86_SMAP), --uaccess,)				\

	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount,)



# Useful for describing the dependency of composite objects

# Usage:

#   $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)

scripts/Makefile.modfinal

+16 −3
Original line number Diff line number Diff line
@@ -9,7 +9,7 @@ __modfinal: 
include include/config/auto.conf

include $(srctree)/scripts/Kbuild.include



# for c_flags

# for c_flags and objtool_args

include $(srctree)/scripts/Makefile.lib



# find all modules listed in modules.order
@@ -34,10 +34,23 @@ ifdef CONFIG_LTO_CLANG 
# With CONFIG_LTO_CLANG, reuse the object file we compiled for modpost to

# avoid a second slow LTO link

prelink-ext := .lto

endif



# ELF processing was skipped earlier because we didn't have native code,

# so let's now process the prelinked binary before we link the module.



ifdef CONFIG_STACK_VALIDATION

ifneq ($(SKIP_STACK_VALIDATION),1)

cmd_ld_ko_o +=								\

	$(objtree)/tools/objtool/objtool $(objtool_args)		\

		$(@:.ko=$(prelink-ext).o);



endif # SKIP_STACK_VALIDATION

endif # CONFIG_STACK_VALIDATION



endif # CONFIG_LTO_CLANG



quiet_cmd_ld_ko_o = LD [M]  $@

      cmd_ld_ko_o =                                                     \

      cmd_ld_ko_o +=							\

	$(LD) -r $(KBUILD_LDFLAGS)					\

		$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)		\

		-T scripts/module.lds -o $@ $(filter %.o, $^);		\

scripts/link-vmlinux.sh

+25 −3
Original line number Diff line number Diff line
@@ -103,14 +103,36 @@ modpost_link() 


objtool_link()

{

	local objtoolcmd;

	local objtoolopt;



	if [ "${CONFIG_LTO_CLANG} ${CONFIG_STACK_VALIDATION}" = "y y" ]; then

		# Don't perform vmlinux validation unless explicitly requested,

		# but run objtool on vmlinux.o now that we have an object file.

		if [ -n "${CONFIG_UNWINDER_ORC}" ]; then

			objtoolcmd="orc generate"

		fi



		objtoolopt="${objtoolopt} --duplicate"



		if [ -n "${CONFIG_FTRACE_MCOUNT_USE_OBJTOOL}" ]; then

			objtoolopt="${objtoolopt} --mcount"

		fi

	fi



	if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then

		objtoolopt="check --vmlinux --noinstr"

		objtoolopt="${objtoolopt} --noinstr"

	fi



	if [ -n "${objtoolopt}" ]; then

		if [ -z "${objtoolcmd}" ]; then

			objtoolcmd="check"

		fi

		objtoolopt="${objtoolopt} --vmlinux"

		if [ -z "${CONFIG_FRAME_POINTER}" ]; then

			objtoolopt="${objtoolopt} --no-fp"

		fi

		if [ -n "${CONFIG_GCOV_KERNEL}" ]; then

		if [ -n "${CONFIG_GCOV_KERNEL}" ] || [ -n "${CONFIG_LTO_CLANG}" ]; then

			objtoolopt="${objtoolopt} --no-unreachable"

		fi

		if [ -n "${CONFIG_RETPOLINE}" ]; then
@@ -120,7 +142,7 @@ objtool_link() 
			objtoolopt="${objtoolopt} --uaccess"

		fi

		info OBJTOOL ${1}

		tools/objtool/objtool ${objtoolopt} ${1}

		tools/objtool/objtool ${objtoolcmd} ${objtoolopt} ${1}

	fi

}