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* [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
@ 2021-02-25 11:20 Arnd Bergmann
  2021-02-25 20:16 ` Kees Cook
                   ` (3 more replies)
  0 siblings, 4 replies; 27+ messages in thread
From: Arnd Bergmann @ 2021-02-25 11:20 UTC (permalink / raw)
  To: Catalin Marinas, Will Deacon, Nathan Chancellor, Nick Desaulniers
  Cc: Arnd Bergmann, Kees Cook, Mark Brown, Vincenzo Frascino,
	Geert Uytterhoeven, Kristina Martsenko, Ionela Voinescu,
	Mark Rutland, Andrew Scull, David Brazdil, Marc Zyngier,
	Ard Biesheuvel, linux-arm-kernel, linux-kernel,
	clang-built-linux

From: Arnd Bergmann <arnd@arndb.de>

When looking at kernel size optimizations, I found that arm64
does not currently support HAVE_LD_DEAD_CODE_DATA_ELIMINATION,
which enables the --gc-sections flag to the linker.

I see that for a defconfig build with llvm, there are some
notable improvements from enabling this, in particular when
combined with the recently added CONFIG_LTO_CLANG_THIN
and CONFIG_TRIM_UNUSED_KSYMS:

   text    data     bss     dec     hex filename
16570322 10998617 506468 28075407 1ac658f defconfig/vmlinux
16318793 10569913 506468 27395174 1a20466 trim_defconfig/vmlinux
16281234 10984848 504291 27770373 1a7be05 gc_defconfig/vmlinux
16029705 10556880 504355 27090940 19d5ffc gc+trim_defconfig/vmlinux
17040142 11102945 504196 28647283 1b51f73 thinlto_defconfig/vmlinux
16788613 10663201 504196 27956010 1aa932a thinlto+trim_defconfig/vmlinux
16347062 11043384 502499 27892945 1a99cd1 gc+thinlto_defconfig/vmlinux
15759453 10532792 502395 26794640 198da90 gc+thinlto+trim_defconfig/vmlinux

I needed a small change to the linker script to get clean randconfig
builds, but I have not done any meaningful boot testing on it to
see if it works. If there are no regressions, I wonder whether this
should be autmatically done for LTO builds, given that it improves
both kernel size and compile speed.

Link: https://lore.kernel.org/lkml/CAK8P3a05VZ9hSKRzVTxTn+1nf9E+gqebJWTj6N23nfm+ELHt9A@mail.gmail.com/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/arm64/Kconfig              | 1 +
 arch/arm64/kernel/vmlinux.lds.S | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b94a678afce4..75e13cc52928 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -2,6 +2,7 @@
 config ARM64
 	def_bool y
 	select ACPI_CCA_REQUIRED if ACPI
+	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	select ACPI_GENERIC_GSI if ACPI
 	select ACPI_GTDT if ACPI
 	select ACPI_IORT if ACPI
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index bad2b9eaab22..926cdb597a45 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -217,7 +217,7 @@ SECTIONS
 		INIT_CALLS
 		CON_INITCALL
 		INIT_RAM_FS
-		*(.init.altinstructions .init.bss .init.bss.*)	/* from the EFI stub */
+		*(.init.altinstructions .init.data.* .init.bss .init.bss.*)	/* from the EFI stub */
 	}
 	.exit.data : {
 		EXIT_DATA
-- 
2.29.2


^ permalink raw reply related	[flat|nested] 27+ messages in thread

end of thread, other threads:[~2021-03-19 14:02 UTC | newest]

Thread overview: 27+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-02-25 11:20 [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION Arnd Bergmann
2021-02-25 20:16 ` Kees Cook
2021-02-26  0:36 ` Sedat Dilek
2021-02-26  8:14   ` Arnd Bergmann
2021-02-26  9:05     ` Sedat Dilek
2021-02-26  9:51       ` Arnd Bergmann
2021-02-26 10:02         ` Sedat Dilek
2021-02-27 20:13           ` Sedat Dilek
2021-02-26 21:13 ` Fangrui Song
2021-02-27  9:49   ` Arnd Bergmann
2021-03-01  1:11     ` Nicholas Piggin
2021-03-10 20:49       ` Masahiro Yamada
2021-03-10 21:08         ` Arnd Bergmann
2021-03-10 21:24           ` Sedat Dilek
2021-03-10 21:47             ` Nicolas Pitre
2021-03-10 21:57               ` Sedat Dilek
2021-03-10 22:02           ` Nick Desaulniers
2021-03-10 22:08             ` Nicolas Pitre
2021-03-10 22:29           ` Fangrui Song
2021-03-10 21:45         ` Rasmus Villemoes
2021-03-10 21:19       ` Nicolas Pitre
2021-03-10 22:42         ` Fangrui Song
2021-03-17 14:37 ` Catalin Marinas
2021-03-17 16:18   ` Catalin Marinas
2021-03-18  8:41     ` Arnd Bergmann
2021-03-19 12:25       ` Catalin Marinas
2021-03-19 14:01         ` Arnd Bergmann

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