Message-ID: <CAF1bQ=RDEPvPvQ4byacTOag4ripc4h6VnTHtr+0Cgmhx39P5Kg@mail.gmail.com>
Date: Tue, 27 May 2025 12:53:18 -0700
From: Rong Xu <xur@...gle.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>, Eric Naim <dnaim@...hyos.org>, 
	Nicolas Schier <nicolas.schier@...ux.dev>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Alice Ryhl <aliceryhl@...gle.com>, 
	Sami Tolvanen <samitolvanen@...gle.com>, "Mike Rapoport (Microsoft)" <rppt@...nel.org>, 
	Rafael Aquini <aquini@...hat.com>, Michael Ellerman <mpe@...erman.id.au>, 
	Stafford Horne <shorne@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	Teresa Johnson <tejohnson@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v3] kbuild: distributed build support for Clang ThinLTO

On Sun, May 25, 2025 at 1:59 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Thu, May 22, 2025 at 6:35 AM <xur@...gle.com> wrote:
> >
> > From: Rong Xu <xur@...gle.com>
> >
> > Add distributed ThinLTO build support for the Linux kernel.
> > This new mode offers several advantages: (1) Increased
> > flexibility in handling user-specified build options.
> > (2) Improved user-friendliness for developers. (3) Greater
> > convenience for integrating with objtool and livepatch.
>
> I did not set up for a distributed build environment, but
> does CC='distcc clang' work to process thin LTO
> on back-end build machines?

I'm sure I get the question. I don't think "distcc clang" works with
in-process ThinLTO build. But I think it works with distributed
ThinLTO (I did not
try myself).

>
>
> You mentioned the benefits (3), but you did not touch
> anything about objtool.

I fixed some bugs in objtool for ThinLTO in some early 5.xx kernel.

>
> How will this patch change the objtool integration?

I haven't looked into the details. But will the availability of native objects
help here?

>
>
>
> >
> > Note that "distributed" in this context refers to a term
> > that differentiates in-process ThinLTO builds by invoking
> > backend compilation through the linker, not necessarily
> > building in distributed environments.
> >
> > Distributed ThinLTO is enabled via the
> > `CONFIG_LTO_CLANG_THIN_DIST` Kconfig option. For example:
> >  > make LLVM=1 defconfig
> >  > scripts/config -e LTO_CLANG_THIN_DIST
> >  > make LLVM=1 oldconfig
> >  > make LLVM=1 vmlinux -j <..>
> >
> > The implementation changes the top-level Makefile with a
> > macro for generating `vmlinux.o` for distributed ThinLTO
> > builds. It uses the existing Kbuild infrastructure to
> > perform two recursive passes through the subdirectories.
> > The first pass generates LLVM IR object files, similar to
> > in-process ThinLTO. Following the thin-link stage, a second
> > pass compiles these IR files into the final native object
> > files. The build rules and actions for this two-pass process
> > are primarily implemented in `scripts/Makefile.build`.
> >
> > Currently, this patch focuses on building the main kernel
> > image (`vmlinux`) only. Support for building kernel modules
> > using this method is planned for a subsequent patch.
> >
> > Tested on the following arch: x86, arm64, loongarch, and
> > riscv.
> >
> > Some implementation details can be found here:
> > https://discourse.llvm.org/t/rfc-distributed-thinlto-build-for-kernel/85934
> >
> > Signed-off-by: Rong Xu <xur@...gle.com>
> > ---
> > Changelog since v1:
> > - Updated the description in arch/Kconfig based on feedback
> >   from Nathan Chancellor
> > - Revised file suffixes: .final_o -> .o.thinlto.native, and
> >   .final_a -> .a.thinlto.native
> > - Updated list of ignored files in .gitignore
> >
> > Changelog since v2:
> > - Changed file suffixes: .o.thinlto.native -> .o_thinlto_native,
> >   and .a.thinlto.native -> .a_thinlto_native so that basename
> >   works as intended.
> > - Tested the patch with AutoFDO and Propeller.
> > ---
>
> > diff --git a/.gitignore b/.gitignore
> > index f2f63e47fb886..b83a68185ef46 100644
> > --- a/.gitignore
> > +++ b/.gitignore
> > @@ -12,6 +12,7 @@
> >  #
> >  .*
> >  *.a
> > +*.a_thinlto_native
>
> This is unneeded.
ack.
>
> >  *.asn1.[ch]
> >  *.bin
> >  *.bz2
> > @@ -39,6 +40,7 @@
> >  *.mod.c
> >  *.o
> >  *.o.*
> > +*.o_thinlto_native
>
> I would rename this to *.thinlto-native.o
> so we do not need to touch .gitignore at all.
ack.
>
>
>
>
>
> >  *.patch
> >  *.rmeta
> >  *.rpm
> > @@ -64,6 +66,7 @@ modules.order
> >  /vmlinux
> >  /vmlinux.32
> >  /vmlinux.map
> > +/vmlinux.thinlink
> >  /vmlinux.symvers
> >  /vmlinux.unstripped
> >  /vmlinux-gdb.py
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index d48dd6726fe6b..f54090f364c93 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -5790,6 +5790,11 @@ F:       scripts/Makefile.clang
> >  F:     scripts/clang-tools/
> >  K:     \b(?i:clang|llvm)\b
> >
> > +CLANG/LLVM THINLTO DISTRIBUTED BUILD
> > +M:     Rong Xu <xur@...gle.com>
> > +S:     Supported
> > +F:     scripts/Makefile.vmlinux_thinlink
> > +
> >  CLK API
> >  M:     Russell King <linux@...linux.org.uk>
> >  L:     linux-clk@...r.kernel.org
> > diff --git a/Makefile b/Makefile
> > index a9edd03036537..8fbff2ab87ebd 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -298,7 +298,8 @@ no-dot-config-targets := $(clean-targets) \
> >                          outputmakefile rustavailable rustfmt rustfmtcheck
> >  no-sync-config-targets := $(no-dot-config-targets) %install modules_sign kernelrelease \
> >                           image_name
> > -single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.rsi %.s %/
> > +single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.rsi %.s %.o_thinlto_native \
> > +                 %.a_thinlto_native %.o.thinlto.bc %/
>
>
> You are adding all new suffixes, but in my understanding there is no way
> to generate %.o.thinlto.bc as a single target.
You are correct. they are generated in batch.
>
>
>
>
>
>
>
>
> >
> >  config-build   :=
> >  mixed-build    :=
> > @@ -991,10 +992,10 @@ export CC_FLAGS_SCS
> >  endif
> >
> >  ifdef CONFIG_LTO_CLANG
> > -ifdef CONFIG_LTO_CLANG_THIN
> > -CC_FLAGS_LTO   := -flto=thin -fsplit-lto-unit
> > -else
> > +ifdef CONFIG_LTO_CLANG_FULL
> >  CC_FLAGS_LTO   := -flto
> > +else # for CONFIG_LTO_CLANG_THIN or CONFIG_LTO_CLANG_THIN_DIST
> > +CC_FLAGS_LTO   := -flto=thin -fsplit-lto-unit
> >  endif
> >  CC_FLAGS_LTO   += -fvisibility=hidden
> >
> > @@ -1213,8 +1214,34 @@ vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
> >         $(call if_changed,ar_vmlinux.a)
> >
> >  PHONY += vmlinux_o
> > +ifdef CONFIG_LTO_CLANG_THIN_DIST
> > +vmlinux.thinlink: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
> > +       $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_thinlink
> > +targets += vmlinux.thinlink
> > +
> > +vmlinux.a_thinlto_native := $(patsubst %.a,%.a_thinlto_native,$(KBUILD_VMLINUX_OBJS))
> > +quiet_cmd_ar_vmlinux.a_thinlto_native = AR      $@
> > +      cmd_ar_vmlinux.a_thinlto_native = \
> > +       rm -f $@; \
> > +       $(AR) cDPrST $@ $(vmlinux.a_thinlto_native); \
> > +       $(AR) mPiT $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
> > +
> > +define rule_gen_vmlinux.a_thinlto_native
> > +       +$(Q)$(MAKE) $(build)=. need-builtin=1 thinlto_final_pass=1 need-modorder=1 built-in.a_thinlto_native
> > +       $(call cmd_and_savecmd,ar_vmlinux.a_thinlto_native)
> > +endef
> > +
> > +vmlinux.a_thinlto_native: vmlinux.thinlink scripts/head-object-list.txt FORCE
> > +       $(call if_changed_rule,gen_vmlinux.a_thinlto_native)
> > +
> > +targets += vmlinux.a_thinlto_native
> > +
> > +vmlinux_o: vmlinux.a_thinlto_native
> > +       $(Q)$(MAKE) thinlto_final_pass=1 -f $(srctree)/scripts/Makefile.vmlinux_o
> > +else
> >  vmlinux_o: vmlinux.a $(KBUILD_VMLINUX_LIBS)
> >         $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_o
> > +endif
> >
> >  vmlinux.o modules.builtin.modinfo modules.builtin: vmlinux_o
> >         @:
> > @@ -1572,7 +1599,8 @@ CLEAN_FILES += vmlinux.symvers modules-only.symvers \
> >                modules.builtin.ranges vmlinux.o.map vmlinux.unstripped \
> >                compile_commands.json rust/test \
> >                rust-project.json .vmlinux.objs .vmlinux.export.c \
> > -               .builtin-dtbs-list .builtin-dtb.S
> > +              .builtin-dtbs-list .builtin-dtb.S \
> > +              .vmlinux_thinlto_bc_files vmlinux.thinlink
> >
> >  # Directories & files removed with 'make mrproper'
> >  MRPROPER_FILES += include/config include/generated          \
> > @@ -2023,6 +2051,8 @@ clean: $(clean-dirs)
> >                 -o -name '*.symtypes' -o -name 'modules.order' \
> >                 -o -name '*.c.[012]*.*' \
> >                 -o -name '*.ll' \
> > +               -o -name '*.a_thinlto_native' -o -name '*.o_thinlto_native' \
> > +               -o -name '*.o.thinlto.bc' \
> >                 -o -name '*.gcno' \
> >                 \) -type f -print \
> >                 -o -name '.tmp_*' -print \
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index b0adb665041f1..30dccda07c671 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -810,6 +810,25 @@ config LTO_CLANG_THIN
> >             https://clang.llvm.org/docs/ThinLTO.html
> >
> >           If unsure, say Y.
> > +
> > +config LTO_CLANG_THIN_DIST
> > +       bool "Clang ThinLTO in distributed mode (EXPERIMENTAL)"
> > +       depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
> > +       select LTO_CLANG
> > +       help
> > +         This option enables Clang's ThinLTO in distributed build mode.
> > +         In this mode, the linker performs the thin-link, generating
> > +         ThinLTO index files. Subsequently, the build system explicitly
> > +         invokes ThinLTO backend compilation using these index files
> > +         and pre-linked IR objects. The resulting native object files
> > +         are with the .o_thinlto_native suffix.
> > +
> > +         This build mode offers improved visibility into the ThinLTO
> > +         process through explicit subcommand exposure. It also makes
> > +         final native object files directly available, benefiting
> > +         tools like objtool and kpatch. Additionally, it provides
> > +         crucial granular control over back-end options, enabling
> > +         module-specific compiler options, and simplifies debugging.
> >  endchoice
> >
> >  config ARCH_SUPPORTS_AUTOFDO_CLANG
> > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > index 13dcd86e74ca8..338e1aec0eaa3 100644
> > --- a/scripts/Makefile.build
> > +++ b/scripts/Makefile.build
> > @@ -50,18 +50,23 @@ endif
> >
> >  # ===========================================================================
> >
> > +builtin_suffix := $(if $(filter %.a_thinlto_native, $(MAKECMDGOALS)),.a_thinlto_native,.a)
> > +ifeq ($(thinlto_final_pass),1)
> > +builtin_suffix :=.a_thinlto_native
> > +endif
> > +
> >  # subdir-builtin and subdir-modorder may contain duplications. Use $(sort ...)
> > -subdir-builtin := $(sort $(filter %/built-in.a, $(real-obj-y)))
> > +subdir-builtin := $(sort $(filter %/built-in$(builtin_suffix), $(real-obj-y)))
> >  subdir-modorder := $(sort $(filter %/modules.order, $(obj-m)))
> >
> >  targets-for-builtin := $(extra-y)
> >
> >  ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),)
> > -targets-for-builtin += $(obj)/lib.a
> > +targets-for-builtin += $(obj)/lib$(builtin_suffix)
> >  endif
> >
> >  ifdef need-builtin
> > -targets-for-builtin += $(obj)/built-in.a
> > +targets-for-builtin += $(obj)/built-in$(builtin_suffix)
> >  endif
> >
> >  targets-for-modules := $(foreach x, o mod, \
> > @@ -337,6 +342,10 @@ $(obj)/%.o: $(obj)/%.S FORCE
> >  targets += $(filter-out $(subdir-builtin), $(real-obj-y))
> >  targets += $(filter-out $(subdir-modorder), $(real-obj-m))
> >  targets += $(lib-y) $(always-y)
> > +ifeq ($(builtin_suffix),.a_thinlto_native)
> > +native_targets = $(patsubst,%.o,%.o_thinlto_native,$(targets))
> > +targets += $(native_targets)
> > +endif
> >
> >  # Linker scripts preprocessor (.lds.S -> .lds)
> >  # ---------------------------------------------------------------------------
> > @@ -347,6 +356,24 @@ quiet_cmd_cpp_lds_S = LDS     $@
> >  $(obj)/%.lds: $(src)/%.lds.S FORCE
> >         $(call if_changed_dep,cpp_lds_S)
> >
> > +ifdef CONFIG_LTO_CLANG_THIN_DIST
> > +# Generate .o_thinlto_native (obj) from .o (bitcode) file
> > +# ---------------------------------------------------------------------------
> > +quiet_cmd_cc_o_bc = CC $(quiet_modtag) $@
> > +
> > +cmd_cc_o_bc      = $(if $(filter bitcode, $(shell file -b $<)),$(CC) \
> > +                  $(filter-out -Wp% $(LINUXINCLUDE) %.h.gch %.h -D% \
> > +                  -flto=thin, $(c_flags)) \
> > +                  -Wno-unused-command-line-argument \
> > +                  -x ir -fthinlto-index=$<.thinlto.bc -c -o $@ \
> > +                  $(if $(findstring ../,$<), \
> > +                  $$(realpath --relative-to=$(srcroot) $<), $<), \
> > +                  cp $< $@)
> > +
> > +$(obj)/%.o_thinlto_native: $(obj)/%.o FORCE
> > +       $(call if_changed,cc_o_bc)
> > +endif
> > +
> >  # ASN.1 grammar
> >  # ---------------------------------------------------------------------------
> >  quiet_cmd_asn1_compiler = ASN.1   $(basename $@).[ch]
> > @@ -360,7 +387,7 @@ $(obj)/%.asn1.c $(obj)/%.asn1.h: $(src)/%.asn1 $(objtree)/scripts/asn1_compiler
> >  # ---------------------------------------------------------------------------
> >
> >  # To build objects in subdirs, we need to descend into the directories
> > -$(subdir-builtin): $(obj)/%/built-in.a: $(obj)/% ;
> > +$(subdir-builtin): $(obj)/%/built-in$(builtin_suffix): $(obj)/% ;
> >  $(subdir-modorder): $(obj)/%/modules.order: $(obj)/% ;
> >
> >  #
> > @@ -377,6 +404,12 @@ quiet_cmd_ar_builtin = AR      $@
> >  $(obj)/built-in.a: $(real-obj-y) FORCE
> >         $(call if_changed,ar_builtin)
> >
> > +ifdef CONFIG_LTO_CLANG_THIN_DIST
> > +# Rule to compile a set of .o_thinlto_native files into one .a_thinlto_native file.
> > +$(obj)/built-in.a_thinlto_native: $(patsubst %.o,%.o_thinlto_native,$(real-obj-y)) FORCE
> > +       $(call if_changed,ar_builtin)
> > +endif
> > +
> >  # This is a list of build artifacts from the current Makefile and its
> >  # sub-directories. The timestamp should be updated when any of the member files.
> >
> > @@ -394,6 +427,14 @@ $(obj)/modules.order: $(obj-m) FORCE
> >  $(obj)/lib.a: $(lib-y) FORCE
> >         $(call if_changed,ar)
> >
> > +ifdef CONFIG_LTO_CLANG_THIN_DIST
> > +quiet_cmd_ar_native = AR      $@
> > +      cmd_ar_native = rm -f $@; $(AR) cDPrsT $@ $(patsubst %.o,%.o_thinlto_native,$(real-prereqs))
> > +
> > +$(obj)/lib.a_thinlto_native: $(patsubst %.o,%.o_thinlto_native,$(lib-y)) FORCE
> > +       $(call if_changed,ar_native)
> > +endif
> > +
> >  quiet_cmd_ld_multi_m = LD [M]  $@
> >        cmd_ld_multi_m = $(LD) $(ld_flags) -r -o $@ @$< $(cmd_objtool)
> >
> > @@ -459,7 +500,8 @@ $(single-subdir-goals): $(single-subdirs)
> >  PHONY += $(subdir-ym)
> >  $(subdir-ym):
> >         $(Q)$(MAKE) $(build)=$@ \
> > -       need-builtin=$(if $(filter $@...ilt-in.a, $(subdir-builtin)),1) \
> > +       need-builtin=$(if $(filter $@...ilt-in$(builtin_suffix), $(subdir-builtin)),1) \
> > +       thinlto_final_pass=$(if $(filter .a_thinlto_native, $(builtin_suffix)),1) \
> >         need-modorder=$(if $(filter $@...dules.order, $(subdir-modorder)),1) \
> >         $(filter $@/%, $(single-subdir-goals))
> >
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index 2fe73cda0bddb..9cfd23590334d 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -34,8 +34,13 @@ else
> >  obj-m := $(filter-out %/, $(obj-m))
> >  endif
> >
> > +builtin_suffix := $(if $(filter %.a_thinlto_native, $(MAKECMDGOALS)),.a_thinlto_native,.a)
> > +ifeq ($(thinlto_final_pass),1)
> > +        builtin_suffix :=.a_thinlto_native
> > +endif
> > +
> >  ifdef need-builtin
> > -obj-y          := $(patsubst %/, %/built-in.a, $(obj-y))
> > +obj-y          := $(patsubst %/, %/built-in$(builtin_suffix), $(obj-y))
> >  else
> >  obj-y          := $(filter-out %/, $(obj-y))
> >  endif
> > diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
> > index b024ffb3e2018..f9abc45a68b36 100644
> > --- a/scripts/Makefile.vmlinux_o
> > +++ b/scripts/Makefile.vmlinux_o
> > @@ -9,6 +9,14 @@ include $(srctree)/scripts/Kbuild.include
> >  # for objtool
> >  include $(srctree)/scripts/Makefile.lib
> >
> > +ifeq ($(thinlto_final_pass),1)
> > +vmlinux_a := vmlinux.a_thinlto_native
> > +vmlinux_libs := $(patsubst %.a,%.a_thinlto_native,$(KBUILD_VMLINUX_LIBS))
> > +else
> > +vmlinux_a := vmlinux.a
> > +vmlinux_libs := $(KBUILD_VMLINUX_LIBS)
> > +endif
> > +
> >  # Generate a linker script to ensure correct ordering of initcalls for Clang LTO
> >  # ---------------------------------------------------------------------------
> >
> > @@ -18,7 +26,7 @@ quiet_cmd_gen_initcalls_lds = GEN     $@
> >         $(PERL) $(real-prereqs) > $@
> >
> >  .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
> > -               vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
> > +               $(vmlinux_a) $(vmlinux_libs) FORCE
> >         $(call if_changed,gen_initcalls_lds)
> >
> >  targets := .tmp_initcalls.lds
> > @@ -59,8 +67,8 @@ quiet_cmd_ld_vmlinux.o = LD      $@
> >         $(LD) ${KBUILD_LDFLAGS} -r -o $@ \
> >         $(vmlinux-o-ld-args-y) \
> >         $(addprefix -T , $(initcalls-lds)) \
> > -       --whole-archive vmlinux.a --no-whole-archive \
> > -       --start-group $(KBUILD_VMLINUX_LIBS) --end-group \
> > +       --whole-archive $(vmlinux_a) --no-whole-archive \
> > +       --start-group $(vmlinux_libs) --end-group \
> >         $(cmd_objtool)
> >
> >  define rule_ld_vmlinux.o
> > @@ -68,7 +76,7 @@ define rule_ld_vmlinux.o
> >         $(call cmd,gen_objtooldep)
> >  endef
> >
> > -vmlinux.o: $(initcalls-lds) vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
> > +vmlinux.o: $(initcalls-lds) $(vmlinux_a) $(vmlinux_libs) FORCE
> >         $(call if_changed_rule,ld_vmlinux.o)
> >
> >  targets += vmlinux.o
> > diff --git a/scripts/Makefile.vmlinux_thinlink b/scripts/Makefile.vmlinux_thinlink
> > new file mode 100644
> > index 0000000000000..13e4026c7d45b
> > --- /dev/null
> > +++ b/scripts/Makefile.vmlinux_thinlink
> > @@ -0,0 +1,53 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +
> > +PHONY := __default
> > +__default: vmlinux.thinlink
> > +
> > +include include/config/auto.conf
> > +include $(srctree)/scripts/Kbuild.include
> > +
> > +
> > +# Generate a linker script to ensure correct ordering of initcalls for Clang LTO
> > +# ---------------------------------------------------------------------------
> > +
> > +quiet_cmd_gen_initcalls_lds = GEN     $@
> > +      cmd_gen_initcalls_lds = \
> > +       $(PYTHON3) $(srctree)/scripts/jobserver-exec \
> > +       $(PERL) $(real-prereqs) > $@
> > +
> > +.tmp_initcalls_thinlink.lds: $(srctree)/scripts/generate_initcall_order.pl \
> > +               vmlinux.a FORCE
> > +       $(call if_changed,gen_initcalls_lds)
> > +
> > +targets := .tmp_initcalls_thinlink.lds
> > +
> > +initcalls-lds := .tmp_initcalls_thinlink.lds
> > +
> > +quiet_cmd_ld_vmlinux.thinlink = LD      $@
> > +      cmd_ld_vmlinux.thinlink = \
> > +       $(AR) t vmlinux.a > .vmlinux_thinlto_bc_files; \
>
>
> Question: Is this a workaround for a linker bug?

You can call it a bug as clang does not handle this.

>
> I wonder why we cannot directly pass vmlinux.a just like
>
> $(LD) ... --thinlto-index-only vmlinux.a

I also think tt should be this way. But currently it does not work.

>
>
>
>
> > +       $(LD) ${KBUILD_LDFLAGS} -r $(addprefix -T , $(initcalls-lds)) \
> > +       --thinlto-index-only @.vmlinux_thinlto_bc_files; \
> > +       touch vmlinux.thinlink
>
>
> Instead of 'touch', I think it is better to use
>
> --thinlto-index-only=$@
ack.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> > +
> > +vmlinux.thinlink: vmlinux.a $(initcalls-lds) FORCE
> > +       $(call if_changed,ld_vmlinux.thinlink)
> > +
> > +targets += vmlinux.thinlink
> > +
> > +# Add FORCE to the prerequisites 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)
> > diff --git a/scripts/head-object-list.txt b/scripts/head-object-list.txt
> > index 7274dfc65af60..90710b87a3877 100644
> > --- a/scripts/head-object-list.txt
> > +++ b/scripts/head-object-list.txt
> > @@ -18,6 +18,7 @@ arch/arm/kernel/head.o
> >  arch/csky/kernel/head.o
> >  arch/hexagon/kernel/head.o
> >  arch/loongarch/kernel/head.o
> > +arch/loongarch/kernel/head.o_thinlto_native
> >  arch/m68k/68000/head.o
> >  arch/m68k/coldfire/head.o
> >  arch/m68k/kernel/head.o
> > --
> > 2.49.0.1143.g0be31eac6b-goog
> >
> >
>
>
> --
> Best Regards
> Masahiro Yamada

Powered by blists - more mailing lists