Re: [PATCH v2 13/28] kbuild: lto: merge module sections

[Masahiro Yamada]

On Fri, Sep 4, 2020 at 5:31 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote:
>
> LLD always splits sections with LTO, which increases module sizes. This
> change adds a linker script that merges the split sections in the final
> module.
>
> Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> ---
>  Makefile               |  2 ++
>  scripts/module-lto.lds | 26 ++++++++++++++++++++++++++
>  2 files changed, 28 insertions(+)
>  create mode 100644 scripts/module-lto.lds
>
> diff --git a/Makefile b/Makefile
> index c69e07bd506a..bb82a4323f1d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -921,6 +921,8 @@ CC_FLAGS_LTO_CLANG += -fvisibility=default
>  # Limit inlining across translation units to reduce binary size
>  LD_FLAGS_LTO_CLANG := -mllvm -import-instr-limit=5
>  KBUILD_LDFLAGS += $(LD_FLAGS_LTO_CLANG)
> +
> +KBUILD_LDS_MODULE += $(srctree)/scripts/module-lto.lds
>  endif
>
>  ifdef CONFIG_LTO
> diff --git a/scripts/module-lto.lds b/scripts/module-lto.lds
> new file mode 100644
> index 000000000000..cbb11dc3639a
> --- /dev/null
> +++ b/scripts/module-lto.lds
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and
> + * -ffunction-sections, which increases the size of the final module.
> + * Merge the split sections in the final binary.
> + */
> +SECTIONS {
> +       __patchable_function_entries : { *(__patchable_function_entries) }
> +
> +       .bss : {
> +               *(.bss .bss.[0-9a-zA-Z_]*)
> +               *(.bss..L*)
> +       }
> +
> +       .data : {
> +               *(.data .data.[0-9a-zA-Z_]*)
> +               *(.data..L*)
> +       }
> +
> +       .rodata : {
> +               *(.rodata .rodata.[0-9a-zA-Z_]*)
> +               *(.rodata..L*)
> +       }
> +
> +       .text : { *(.text .text.[0-9a-zA-Z_]*) }
> +}
> --
> 2.28.0.402.g5ffc5be6b7-goog
>


After I apply https://patchwork.kernel.org/patch/11757323/,
is it possible to do like this ?


#ifdef CONFIG_LTO
SECTIONS {
     ...
};
#endif

in scripts/module.lds.S


-- 
Best Regards
Masahiro Yamada