linux-kernel - [PATCH] [RFT] m68k: enable HAVE_LD_DEAD_CODE_DATA

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Message-Id: <20210225111505.1936566-1-arnd@kernel.org>
Date:   Thu, 25 Feb 2021 12:14:45 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: [PATCH] [RFT] m68k: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

From: Arnd Bergmann <arnd@...db.de>

While experimenting with CONFIG_TRIM_UNUSED_KSYMS across architectures,
I noticed that this unsurprisingly works best when combined with the
--gc-sections linker flag, which is not currently allowed on m68k.

Enabling it with this patch shows significant improvements
for kernel size, looking at m68k defconfig with gcc-10, I get

4005135 1374302 167108 5546545 54a231 vmlinux-normal
3916254 1378078 167108 5461440 5355c0 vmlinux+trim
4012933 1362514 164280 5539727 54878f vmlinux+gcsection
3797884 1334194 164640 5296718 50d24e vmlinux+gcsection+trim

There are probably bugs somewhere, but if someone is able to test this
patch and fix any issues that come up, would be a useful improvement
for memory-limited machines.

Link: https://lore.kernel.org/lkml/CAK8P3a05VZ9hSKRzVTxTn+1nf9E+gqebJWTj6N23nfm+ELHt9A@mail.gmail.com/
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/m68k/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index c186733562b3..5f1aafa7b2e2 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -24,6 +24,7 @@ config M68K
 	select HAVE_DEBUG_BUGVERBOSE
 	select HAVE_FUTEX_CMPXCHG if MMU && FUTEX
 	select HAVE_IDE
+	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_UID16
 	select MMU_GATHER_NO_RANGE if MMU
-- 
2.29.2