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

[Yonghong Song <yonghong.song@linux.dev>]

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!

>
> Best regards,