Messages in this thread Patch in this message | | | From | Arnd Bergmann <> | Subject | [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION | Date | Thu, 25 Feb 2021 12:20:56 +0100 |
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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
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