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Message-ID: <CAK7LNARnh-7a8Lq-y2u72cnk2uxSuWxjaZ8Y-JHCYu5gwt7Ekg@mail.gmail.com>
Date: Tue, 8 Sep 2020 00:25:54 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Kees Cook <keescook@...omium.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arch <linux-arch@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-pci@...r.kernel.org, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v2 13/28] kbuild: lto: merge module sections
On Fri, Sep 4, 2020 at 5:31 AM Sami Tolvanen <samitolvanen@...gle.com> 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@...gle.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
> 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
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