Re: [PATCH kbuild v2] kbuild: Reduce the number of compiler-generated suffixes for clang thin-lto build

[Nicolas Schier <nsc@kernel.org>]

On Sun, Mar 15, 2026 at 09:37:22AM -0700, Yonghong Song wrote:
> 
> 
> On 3/12/26 7:12 AM, Nicolas Schier wrote:
> > On Fri, 06 Mar 2026 21:02:50 -0800, Yonghong Song wrote:
> > > The current clang thin-lto build often produces lots of symbols with
> > > suffix. The following is a partial list of such function call symbols:
> > >      ...
> > >      ethnl_module_fw_flash_ntf.llvm.7631589765585346066
> > >      __nf_conntrack_alloc.llvm.6438426151906658917
> > >      tcp_can_early_drop.llvm.11937612064648250727
> > >      tcp_print_conntrack.llvm.11937612064648250727
> > >      ...
> > > 
> > > [...]
> > Note: Due to application of [1] to kbuild-next-unstable, I had to update the
> >        patch context.
> > 
> > [1]: https://lore.kernel.org/linux-kbuild/20251028182822.3210436-1-xur@google.com/
> > 
> > 
> > 
> > Applied to kbuild/kbuild-next.git (kbuild-next-unstable), thanks!
> > 
> > [1/1] kbuild: Reduce the number of compiler-generated suffixes for clang thin-lto build
> >        https://git.kernel.org/kbuild/c/b7a7ce34
> > 
> > Please look out for regression or issue reports or other follow up
> > comments, as they may result in the patch/series getting dropped,
> > reverted or modified (e.g. trailers). Patches applied to the
> > kbuild-next-unstable branch are accepted pending wider testing in
> > linux-next and any post-commit review; they will generally be moved
> > to the kbuild-next branch in about a week if no issues are found.
> 
> Thanks, Nicolas,
> 
> I looked at the patch [1] and find that my patch needs some change.
> The current change is
> 
> @@ -1047,6 +1047,7 @@ CC_FLAGS_LTO := -flto
> else
> CC_FLAGS_LTO := -flto=thin -fsplit-lto-unit
> +KBUILD_LDFLAGS += $(call ld-option,--lto-whole-program-visibility -mllvm
> -always-rename-promoted-locals=false)
> endif
> CC_FLAGS_LTO += -fvisibility=hidden Due to [1], the above change should be
> @@ -1047,6 +1047,7 @@ CC_FLAGS_LTO := -flto
> else
> CC_FLAGS_LTO := -flto=thin -fsplit-lto-unit
> +if CONFIG_LTO_CLANG_THIN
> +KBUILD_LDFLAGS += $(call ld-option,--lto-whole-program-visibility -mllvm
> -always-rename-promoted-locals=false)
> +endif
> endif
> CC_FLAGS_LTO += -fvisibility=hidden
> 
> The reason likes below:
> 
> The patch [1] introduced CONFOG_LTO_CLANG_THIN_DIST and in Makefile, for the following change:
> 
>  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 +CC_FLAGS_LTO := -flto=thin -fsplit-lto-unit  endif
>  CC_FLAGS_LTO	+= -fvisibility=hidden
> 
> The else branch 'CC_FLAGS_LTO := -flto=thin -fsplit-lto-unit' will support both CONFIG_LTO_CLANG_THIN and CONFIG_LTO_CLANG_THIN_DIST.
> 
> My patch commit message mentioned that the new flag won't support
> thinlto distributed mode yet. So The new ldflags
>   $(call ld-option,--lto-whole-program-visibility -mllvm
> -always-rename-promoted-locals=false) needs under LTO_CLANG_THIN but not
> LTO_CLANG_THIN_DIST. There will be some effort in llvm to support
> distributed thin-lto as well for suffix reduction. But it may take a little
> bit time as llvm needs some infrastructure change before supporting
> distributed thin-lto. Thanks!

Thanks a lot!  I changed the commit as instructed:

$ git range-diff b7a7ce345daa...6a76b3c06a1d
1:  b7a7ce345daa ! 1:  6a76b3c06a1d kbuild: Reduce the number of compiler-generated suffixes for clang thin-lto build
    @@ Makefile: ifdef CONFIG_LTO_CLANG_FULL
      CC_FLAGS_LTO      := -flto
      else
      CC_FLAGS_LTO      := -flto=thin -fsplit-lto-unit
    ++if CONFIG_LTO_CLANG_THIN
     +KBUILD_LDFLAGS += $(call ld-option,--lto-whole-program-visibility -mllvm -always-rename-promoted-locals=false)
    ++endif
      endif
      CC_FLAGS_LTO      += -fvisibility=hidden


and it is pushed to kbuild/kbuild-next-unstable
https://git.kernel.org/kbuild/c/6a76b3c06a1d359a3e84c37bc0fead370f6ccfc0


-- 
Nicolas