mirror of
https://github.com/torvalds/linux.git
synced 2024-11-10 14:11:52 +00:00
c25e1c5582
When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created
for each module. Also, objtool is postponed until LLVM IR is converted
to ELF.
CONFIG_X86_KERNEL_IBT works in a similar way to postpone objtool until
objects are merged together.
This commit stops generating *.prelink.o, so the build flow will look
similar with/without LTO.
The following figures show how the LTO build currently works, and
how this commit is changing it.
Current build flow
==================
[1] single-object module
$(LD)
$(CC) +objtool $(LD)
foo.c --------------------> foo.o -----> foo.prelink.o -----> foo.ko
(LLVM IR) (ELF) | (ELF)
|
foo.mod.o --/
(LLVM IR)
[2] multi-object module
$(LD)
$(CC) $(AR) +objtool $(LD)
foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko
| (archive) (ELF) | (ELF)
foo2.c -----> foo2.o --/ |
(LLVM IR) foo.mod.o --/
(LLVM IR)
One confusion is that foo.o in multi-object module is an archive
despite of its suffix.
New build flow
==============
[1] single-object module
Since there is only one object, there is no need to keep the LLVM IR.
Use $(CC)+$(LD) to generate an ELF object in one build rule. When LTO
is disabled, $(LD) is unneeded because $(CC) produces an ELF object.
$(CC)+$(LD)+objtool $(LD)
foo.c ----------------------------> foo.o ---------> foo.ko
(ELF) | (ELF)
|
foo.mod.o --/
(LLVM IR)
[2] multi-object module
Previously, $(AR) was used to combine LLVM IR files into an archive,
but there was no technical reason to do so. Use $(LD) to merge them
into a single ELF object.
$(LD)
$(CC) +objtool $(LD)
foo1.c ---------> foo1.o ---------> foo.o ---------> foo.ko
| (ELF) | (ELF)
foo2.c ---------> foo2.o ----/ |
(LLVM IR) foo.mod.o --/
(LLVM IR)
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
209 lines
7.4 KiB
Plaintext
209 lines
7.4 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0
|
|
####
|
|
# kbuild: Generic definitions
|
|
|
|
# Convenient variables
|
|
comma := ,
|
|
quote := "
|
|
squote := '
|
|
empty :=
|
|
space := $(empty) $(empty)
|
|
space_escape := _-_SPACE_-_
|
|
pound := \#
|
|
|
|
###
|
|
# Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
|
|
dot-target = $(dir $@).$(notdir $@)
|
|
|
|
###
|
|
# Name of target with a '.tmp_' as filename prefix. foo/bar.o => foo/.tmp_bar.o
|
|
tmp-target = $(dir $@).tmp_$(notdir $@)
|
|
|
|
###
|
|
# The temporary file to save gcc -MMD generated dependencies must not
|
|
# contain a comma
|
|
depfile = $(subst $(comma),_,$(dot-target).d)
|
|
|
|
###
|
|
# filename of target with directory and extension stripped
|
|
basetarget = $(basename $(notdir $@))
|
|
|
|
###
|
|
# real prerequisites without phony targets
|
|
real-prereqs = $(filter-out $(PHONY), $^)
|
|
|
|
###
|
|
# Escape single quote for use in echo statements
|
|
escsq = $(subst $(squote),'\$(squote)',$1)
|
|
|
|
###
|
|
# Quote a string to pass it to C files. foo => '"foo"'
|
|
stringify = $(squote)$(quote)$1$(quote)$(squote)
|
|
|
|
###
|
|
# Easy method for doing a status message
|
|
kecho := :
|
|
quiet_kecho := echo
|
|
silent_kecho := :
|
|
kecho := $($(quiet)kecho)
|
|
|
|
###
|
|
# filechk is used to check if the content of a generated file is updated.
|
|
# Sample usage:
|
|
#
|
|
# filechk_sample = echo $(KERNELRELEASE)
|
|
# version.h: FORCE
|
|
# $(call filechk,sample)
|
|
#
|
|
# The rule defined shall write to stdout the content of the new file.
|
|
# The existing file will be compared with the new one.
|
|
# - If no file exist it is created
|
|
# - If the content differ the new file is used
|
|
# - If they are equal no change, and no timestamp update
|
|
define filechk
|
|
$(check-FORCE)
|
|
$(Q)set -e; \
|
|
mkdir -p $(dir $@); \
|
|
trap "rm -f $(dot-target).tmp" EXIT; \
|
|
{ $(filechk_$(1)); } > $(dot-target).tmp; \
|
|
if [ ! -r $@ ] || ! cmp -s $@ $(dot-target).tmp; then \
|
|
$(kecho) ' UPD $@'; \
|
|
mv -f $(dot-target).tmp $@; \
|
|
fi
|
|
endef
|
|
|
|
###
|
|
# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
|
|
# Usage:
|
|
# $(Q)$(MAKE) $(build)=dir
|
|
build := -f $(srctree)/scripts/Makefile.build obj
|
|
|
|
###
|
|
# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.dtbinst obj=
|
|
# Usage:
|
|
# $(Q)$(MAKE) $(dtbinst)=dir
|
|
dtbinst := -f $(srctree)/scripts/Makefile.dtbinst obj
|
|
|
|
###
|
|
# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.clean obj=
|
|
# Usage:
|
|
# $(Q)$(MAKE) $(clean)=dir
|
|
clean := -f $(srctree)/scripts/Makefile.clean obj
|
|
|
|
# echo command.
|
|
# Short version is used, if $(quiet) equals `quiet_', otherwise full one.
|
|
echo-cmd = $(if $($(quiet)cmd_$(1)),\
|
|
echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
|
|
|
|
# sink stdout for 'make -s'
|
|
redirect :=
|
|
quiet_redirect :=
|
|
silent_redirect := exec >/dev/null;
|
|
|
|
# printing commands
|
|
cmd = @set -e; $(echo-cmd) $($(quiet)redirect) $(cmd_$(1))
|
|
|
|
###
|
|
# if_changed - execute command if any prerequisite is newer than
|
|
# target, or command line has changed
|
|
# if_changed_dep - as if_changed, but uses fixdep to reveal dependencies
|
|
# including used config symbols
|
|
# if_changed_rule - as if_changed but execute rule instead
|
|
# See Documentation/kbuild/makefiles.rst for more info
|
|
|
|
ifneq ($(KBUILD_NOCMDDEP),1)
|
|
# Check if both commands are the same including their order. Result is empty
|
|
# string if equal. User may override this check using make KBUILD_NOCMDDEP=1
|
|
cmd-check = $(filter-out $(subst $(space),$(space_escape),$(strip $(cmd_$@))), \
|
|
$(subst $(space),$(space_escape),$(strip $(cmd_$1))))
|
|
else
|
|
cmd-check = $(if $(strip $(cmd_$@)),,1)
|
|
endif
|
|
|
|
# Replace >$< with >$$< to preserve $ when reloading the .cmd file
|
|
# (needed for make)
|
|
# Replace >#< with >$(pound)< to avoid starting a comment in the .cmd file
|
|
# (needed for make)
|
|
# Replace >'< with >'\''< to be able to enclose the whole string in '...'
|
|
# (needed for the shell)
|
|
make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
|
|
|
|
# Find any prerequisites that are newer than target or that do not exist.
|
|
# (This is not true for now; $? should contain any non-existent prerequisites,
|
|
# but it does not work as expected when .SECONDARY is present. This seems a bug
|
|
# of GNU Make.)
|
|
# PHONY targets skipped in both cases.
|
|
newer-prereqs = $(filter-out $(PHONY),$?)
|
|
|
|
# It is a typical mistake to forget the FORCE prerequisite. Check it here so
|
|
# no more breakage will slip in.
|
|
check-FORCE = $(if $(filter FORCE, $^),,$(warning FORCE prerequisite is missing))
|
|
|
|
if-changed-cond = $(newer-prereqs)$(cmd-check)$(check-FORCE)
|
|
|
|
# Execute command if command has changed or prerequisite(s) are updated.
|
|
if_changed = $(if $(if-changed-cond), \
|
|
$(cmd); \
|
|
printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
|
|
|
|
# Execute the command and also postprocess generated .d dependencies file.
|
|
if_changed_dep = $(if $(if-changed-cond),$(cmd_and_fixdep),@:)
|
|
|
|
cmd_and_fixdep = \
|
|
$(cmd); \
|
|
scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).cmd;\
|
|
rm -f $(depfile)
|
|
|
|
# Usage: $(call if_changed_rule,foo)
|
|
# Will check if $(cmd_foo) or any of the prerequisites changed,
|
|
# and if so will execute $(rule_foo).
|
|
if_changed_rule = $(if $(if-changed-cond),$(rule_$(1)),@:)
|
|
|
|
###
|
|
# why - tell why a target got built
|
|
# enabled by make V=2
|
|
# Output (listed in the order they are checked):
|
|
# (1) - due to target is PHONY
|
|
# (2) - due to target missing
|
|
# (3) - due to: file1.h file2.h
|
|
# (4) - due to command line change
|
|
# (5) - due to missing .cmd file
|
|
# (6) - due to target not in $(targets)
|
|
# (1) PHONY targets are always build
|
|
# (2) No target, so we better build it
|
|
# (3) Prerequisite is newer than target
|
|
# (4) The command line stored in the file named dir/.target.cmd
|
|
# differed from actual command line. This happens when compiler
|
|
# options changes
|
|
# (5) No dir/.target.cmd file (used to store command line)
|
|
# (6) No dir/.target.cmd file and target not listed in $(targets)
|
|
# This is a good hint that there is a bug in the kbuild file
|
|
ifeq ($(KBUILD_VERBOSE),2)
|
|
why = \
|
|
$(if $(filter $@, $(PHONY)),- due to target is PHONY, \
|
|
$(if $(wildcard $@), \
|
|
$(if $(newer-prereqs),- due to: $(newer-prereqs), \
|
|
$(if $(cmd-check), \
|
|
$(if $(cmd_$@),- due to command line change, \
|
|
$(if $(filter $@, $(targets)), \
|
|
- due to missing .cmd file, \
|
|
- due to $(notdir $@) not in $$(targets) \
|
|
) \
|
|
) \
|
|
) \
|
|
), \
|
|
- due to target missing \
|
|
) \
|
|
)
|
|
|
|
echo-why = $(call escsq, $(strip $(why)))
|
|
endif
|
|
|
|
###############################################################################
|
|
|
|
# delete partially updated (i.e. corrupted) files on error
|
|
.DELETE_ON_ERROR:
|
|
|
|
# do not delete intermediate files automatically
|
|
.SECONDARY:
|