Re: [PATCH v9 3/3] kbuild: distributed build support for Clang ThinLTO

[Rong Xu]

Yonghong, thanks for the update.

Regarding this guard: ther is a period of Clang (before this patch and
after your first patch), even though ld.lld having these options
(specifically --lto-whole-program-visibility -mllvm
-always-rename-promoted-locals=false), distributed ThinLTO mode
remains unsupported, correct? What the behvior of using this options
in distributed mode with these compilers? nop or it will lead to
error?

I would assume there will be errors; otherwise, you would not ask me
to change my patch last time. In this case, I would keep this guard
and remove it when the minimum llvm version passes llvm23. What do you
think?

Best,

-Rong


On Thu, May 21, 2026 at 1:57 PM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
>
>
> On 3/31/26 9:27 AM, Nathan Chancellor wrote:
> > Hi Rong,
> >
> > On Tue, Mar 31, 2026 at 03:48:27PM +0000, xur@xxxxxxxxxx wrote:
> >> diff --git a/Makefile b/Makefile
> >> index 69ccf9b8507d..26005c64016d 100644
> >> --- a/Makefile
> >> +++ b/Makefile
> >> @@ -1047,11 +1047,13 @@ export CC_FLAGS_SCS
> >>   endif
> >>
> >>   ifdef CONFIG_LTO_CLANG
> >> -ifdef CONFIG_LTO_CLANG_THIN
> >> +ifdef CONFIG_LTO_CLANG_FULL
> >> +CC_FLAGS_LTO        := -flto
> >> +else
> >>   CC_FLAGS_LTO       := -flto=thin -fsplit-lto-unit
> >> +if CONFIG_LTO_CLANG_THIN
> > This should be an 'ifdef', not an 'if'. You copied Yonghong's mistake:
> >
> >    https://lore.kernel.org/abgRRX3PH9IaExi8@xxxxxxxxxxxxx/
> >    https://lore.kernel.org/6db3a2f6-d61c-42f1-9b9d-0aca021cc2d7@xxxxxxxxx/
> >
> > Please slow down and test build your changes before sending them. Each
> > revision adds four new emails to everyone's inbox, which is just noise
> > when there are obvious, basic problems. 'b4 diff' shows no actual
> > difference from v8 and v9, which should have been caught by a simple
> > build test right before 'git send-email'.
> >
> >>   KBUILD_LDFLAGS += $(call ld-option,--lto-whole-program-visibility -mllvm -always-rename-promoted-locals=false)
> >> -else
> >> -CC_FLAGS_LTO        := -flto
> >> +endif
>
> The above patch has a guard CONFIG_LTO_CLANG_THIN, which can be removed.
> See llvm patch
>     https://github.com/llvm/llvm-project/pull/188074
> which supports distributed thin-lto mode too for reducing the number
> of renaming. In other words, for llvm23, both in-process and
> distributed-process are supported for thin-lto.
>
> >>   endif
> >>   CC_FLAGS_LTO       += -fvisibility=hidden
> >>
> >> @@ -1657,6 +1659,7 @@ endif # CONFIG_MODULES
> >>   CLEAN_FILES += vmlinux.symvers modules-only.symvers \
> >>             modules.builtin modules.builtin.modinfo modules.nsdeps \
> >>             modules.builtin.ranges vmlinux.o.map vmlinux.unstripped \
> >> +           vmlinux.thinlto-index builtin.order \
> >>             compile_commands.json rust/test \
> >>             rust-project.json .vmlinux.objs .vmlinux.export.c \
> >>                  .builtin-dtbs-list .builtin-dtb.S
> >> @@ -2118,7 +2121,7 @@ clean: $(clean-dirs)
> >>      $(call cmd,rmfiles)
> >>      @find . $(RCS_FIND_IGNORE) \
> >>              \( -name '*.[aios]' -o -name '*.rsi' -o -name '*.ko' -o -name '.*.cmd' \
> >> -            -o -name '*.ko.*' \
> >> +            -o -name '*.ko.*' -o -name '*.o.thinlto.bc' \
> >>              -o -name '*.dtb' -o -name '*.dtbo' \
> >>              -o -name '*.dtb.S' -o -name '*.dtbo.S' \
> >>              -o -name '*.dt.yaml' -o -name 'dtbs-list' \
> > With that addressed above, the series survives my basic LLVM 22.1.2
> > build test with my distribution configuration. I'll provide formal tags
> > on a properly tested and fixed revision.
> >
> > Cheers,
> > Nathan
>