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kbuild: lto: postpone objtool

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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: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Sami Tolvanen 2020-04-13 16:10:13 -07:00 committed by Kees Cook
parent 41425ebe20
commit b1a1a1a09b
4 changed files with 55 additions and 26 deletions
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22
scripts/Makefile.build
View File

@ -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.

12
scripts/Makefile.lib
View File

@ -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)

19
scripts/Makefile.modfinal
View File

@ -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, $^); \

28
scripts/link-vmlinux.sh
View File

@ -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
}