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Date: Wed, 14 Oct 2020 15:49:10 -0700
From: Kees Cook <keescook@...omium.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>, Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux@...glegroups.com,
kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
x86@...nel.org
Subject: Re: [PATCH v6 13/25] kbuild: lto: merge module sections
On Mon, Oct 12, 2020 at 05:31:51PM -0700, Sami Tolvanen wrote:
> LLD always splits sections with LTO, which increases module sizes. This
> change adds linker script rules to merge the split sections in the final
> module.
>
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> ---
> scripts/module.lds.S | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/scripts/module.lds.S b/scripts/module.lds.S
> index 69b9b71a6a47..037120173a22 100644
> --- a/scripts/module.lds.S
> +++ b/scripts/module.lds.S
> @@ -25,5 +25,33 @@ SECTIONS {
> __jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) }
> }
>
> +#ifdef CONFIG_LTO_CLANG
In looking at this again -- is this ifdef needed? Couldn't this be done
unconditionally? (Which would make it an independent change...)
-Kees
> +/*
> + * 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_]*) }
> +}
> +#endif
> +
> /* bring in arch-specific sections */
> #include <asm/module.lds.h>
> --
> 2.28.0.1011.ga647a8990f-goog
>
--
Kees Cook
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