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From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Tue, 11 Jun 2024 14:45:14 +0200
Message-ID: <CAMuHMdWMAg59p+hzeLG9Uc3X55Vt9ccNy5BRoPX0RJbxrMOFLA@mail.gmail.com>
Subject: Re: [PATCH-next v4] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
To: Yuntao Liu <liuyuntao12@huawei.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, 
	arnd@arndb.de, ardb@kernel.org, linux@armlinux.org.uk, afd@ti.com, 
	akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, corbet@lwn.net, 
	rppt@kernel.org, robh@kernel.org, tglx@linutronix.de, 
	linus.walleij@linaro.org, maskray@google.com, 
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>, Chris Brandt <Chris.Brandt@renesas.com>
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Hi Yuntao,

On Sat, Mar 16, 2024 at 3:44=E2=80=AFAM Yuntao Liu <liuyuntao12@huawei.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@huawei.com>
> Tested-by: Arnd Bergmann <arnd@arndb.de>
> Reviewed-by: Arnd Bergmann <arnd@arndb.de>

Thanks for your patch, which is now commit ed0f941022515ff4 ("ARM:
9404/1: arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION") in
arm/for-next (next-20240611).

I gave this a try on my custom configs for RSK+RZA1 (RZ/A1H)
and RZA2MEVB (RZ/A2M).  According to bloat-o-meter, enabling
HAVE_LD_DEAD_CODE_DATA_ELIMINATION reduced kernel size by almost
500 KiB (-8.3%).  The figures reported in "Memory: ... available"
were even more impressive: 1032 KiB more free memory than before.

As these boards have only 32 resp. 64 MiB of RAM, and some products
even use RZ/A1H with just the 10 MiB of on-chip SRAM, this is a good
improvement to have!
Thanks!

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
.org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds