Messages in this thread | | | From | Sedat Dilek <> | Date | Fri, 26 Feb 2021 01:36:02 +0100 | Subject | Re: [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION |
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On Thu, Feb 25, 2021 at 12:21 PM Arnd Bergmann <arnd@kernel.org> wrote: > > 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 >
Thanks for the numbers. Does CONFIG_TRIM_UNUSED_KSYMS=y have an impact to the build-time (and disc-usage - negative way means longer/bigger)? Do you have any build-time for the above numbers?
BTW, is CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y setable for x86 (64bit)? ( Did not look or check for it. )
- Sedat -
> 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 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20210225112122.2198845-1-arnd%40kernel.org.
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