mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-01 08:04:22 +08:00
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>
82 lines
2.7 KiB
Makefile
82 lines
2.7 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0-only
|
|
# ===========================================================================
|
|
# Module final link
|
|
# ===========================================================================
|
|
|
|
PHONY := __modfinal
|
|
__modfinal:
|
|
|
|
include include/config/auto.conf
|
|
include $(srctree)/scripts/Kbuild.include
|
|
|
|
# for c_flags
|
|
include $(srctree)/scripts/Makefile.lib
|
|
|
|
# find all modules listed in modules.order
|
|
modules := $(sort $(shell cat $(MODORDER)))
|
|
|
|
__modfinal: $(modules)
|
|
@:
|
|
|
|
# modname and part-of-module are set to make c_flags define proper module flags
|
|
modname = $(notdir $(@:.mod.o=))
|
|
part-of-module = y
|
|
|
|
quiet_cmd_cc_o_c = CC [M] $@
|
|
cmd_cc_o_c = $(CC) $(filter-out $(CC_FLAGS_CFI), $(c_flags)) -c -o $@ $<
|
|
|
|
%.mod.o: %.mod.c FORCE
|
|
$(call if_changed_dep,cc_o_c)
|
|
|
|
ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
|
|
|
|
quiet_cmd_ld_ko_o = LD [M] $@
|
|
cmd_ld_ko_o += \
|
|
$(LD) -r $(KBUILD_LDFLAGS) \
|
|
$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
|
|
-T scripts/module.lds -o $@ $(filter %.o, $^); \
|
|
$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
|
|
|
|
quiet_cmd_btf_ko = BTF [M] $@
|
|
cmd_btf_ko = \
|
|
if [ -f vmlinux ]; then \
|
|
LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) --btf_base vmlinux $@; \
|
|
$(RESOLVE_BTFIDS) -b vmlinux $@; \
|
|
else \
|
|
printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
|
|
fi;
|
|
|
|
# Same as newer-prereqs, but allows to exclude specified extra dependencies
|
|
newer_prereqs_except = $(filter-out $(PHONY) $(1),$?)
|
|
|
|
# Same as if_changed, but allows to exclude specified extra dependencies
|
|
if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \
|
|
$(cmd); \
|
|
printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
|
|
|
|
# Re-generate module BTFs if either module's .ko or vmlinux changed
|
|
$(modules): %.ko: %.o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
|
|
+$(call if_changed_except,ld_ko_o,vmlinux)
|
|
ifdef CONFIG_DEBUG_INFO_BTF_MODULES
|
|
+$(if $(newer-prereqs),$(call cmd,btf_ko))
|
|
endif
|
|
|
|
targets += $(modules) $(modules:.ko=.mod.o)
|
|
|
|
# Add FORCE to the prequisites of a target to force it to be always rebuilt.
|
|
# ---------------------------------------------------------------------------
|
|
|
|
PHONY += FORCE
|
|
FORCE:
|
|
|
|
# Read all saved command lines and dependencies for the $(targets) we
|
|
# may be building above, using $(if_changed{,_dep}). As an
|
|
# optimization, we don't need to read them if the target does not
|
|
# exist, we will rebuild anyway in that case.
|
|
|
|
existing-targets := $(wildcard $(sort $(targets)))
|
|
|
|
-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
|
|
|
|
.PHONY: $(PHONY)
|