linux-kernel - Re: [PATCH-next v4] arm32: enable HAVE_LD_DEAD_CODE_DATA

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Message-ID: <CAMj1kXH5bpbagOO+WFwxp4=U=Kbu9RVbPrEemt80S7My1jTEdw@mail.gmail.com>
Date: Tue, 19 Mar 2024 18:12:56 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Yuntao Liu <liuyuntao12@...wei.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	arnd@...db.de, geert@...ux-m68k.org, linux@...linux.org.uk, afd@...com, 
	akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com, 
	geert+renesas@...der.be, corbet@....net, rppt@...nel.org, robh@...nel.org, 
	tglx@...utronix.de, linus.walleij@...aro.org, maskray@...gle.com
Subject: Re: [PATCH-next v4] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

On Sat, 16 Mar 2024 at 03:44, Yuntao Liu <liuyuntao12@...wei.com> wrote:
>
> The current arm32 architecture does not yet support the
> HAVE_LD_DEAD_CODE_DATA_ELIMINATION feature. arm32 is widely used in
> embedded scenarios, and enabling this feature would be beneficial for
> reducing the size of the kernel image.
>
> In order to make this work, we keep the necessary tables by annotating
> them with KEEP, also it requires further changes to linker script to KEEP
> some tables and wildcard compiler generated sections into the right place.
> When using ld.lld for linking, KEEP is not recognized within the OVERLAY
> command, and Ard proposed a concise method to solve this problem.
>
> It boots normally with defconfig, vexpress_defconfig and tinyconfig.
>
> The size comparison of zImage is as follows:
> defconfig       vexpress_defconfig      tinyconfig
> 5137712         5138024                 424192          no dce
> 5032560         4997824                 298384          dce
> 2.0%            2.7%                    29.7%           shrink
>
> When using smaller config file, there is a significant reduction in the
> size of the zImage.
>
> We also tested this patch on a commercially available single-board
> computer, and the comparison is as follows:
> a15eb_config
> 2161384         no dce
> 2092240         dce
> 3.2%            shrink
>
> The zImage size has been reduced by approximately 3.2%, which is 70KB on
> 2.1M.
>
> Signed-off-by: Yuntao Liu <liuyuntao12@...wei.com>
> Tested-by: Arnd Bergmann <arnd@...db.de>
> Reviewed-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Ard Biesheuvel <ardb@...nel.org>