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

[Yonghong Song]

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