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libs: libc: armv8-m: Enable ARMV8M_STRING_FUNCTION #18950

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libs: libc: armv8-m: Enable ARMV8M_STRING_FUNCTION #18950

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libs: libc: armv8-m: Enable ARMV8M_STRING_FUNCTION
patrickelectric May 24, 2026
90752dc
boards: imx93-qsb: Disable ARMV8M_STRING_FUNCTION
patrickelectric May 28, 2026
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1 change: 1 addition & 0 deletions boards/arm/imx9/imx93-qsb/configs/nsh-ddr/defconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ CONFIG_ARCH_INTERRUPTSTACK=4096
CONFIG_ARCH_STACKDUMP=y
CONFIG_ARMV8M_DTCM=y
CONFIG_ARMV8M_ITCM=y
CONFIG_ARMV8M_STRING_FUNCTION=n
CONFIG_BOARD_LOOPSPERMSEC=613
CONFIG_BOOT_RUNFROMSDRAM=y
CONFIG_BUILTIN=y
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1 change: 1 addition & 0 deletions boards/arm/imx9/imx93-qsb/configs/nsh/defconfig
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Expand Up @@ -18,6 +18,7 @@ CONFIG_ARCH_INTERRUPTSTACK=4096
CONFIG_ARCH_STACKDUMP=y
CONFIG_ARMV8M_DTCM=y
CONFIG_ARMV8M_ITCM=y
CONFIG_ARMV8M_STRING_FUNCTION=n
CONFIG_BOARD_LOOPSPERMSEC=2399
CONFIG_BOOT_RUNFROMISRAM=y
CONFIG_BUILTIN=y
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1 change: 1 addition & 0 deletions boards/arm/imx9/imx93-qsb/configs/rpmsg/defconfig
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Expand Up @@ -18,6 +18,7 @@ CONFIG_ARCH_INTERRUPTSTACK=4096
CONFIG_ARCH_STACKDUMP=y
CONFIG_ARMV8M_DTCM=y
CONFIG_ARMV8M_ITCM=y
CONFIG_ARMV8M_STRING_FUNCTION=n
CONFIG_BOARD_LOOPSPERMSEC=2399
CONFIG_BOOT_RUNFROMISRAM=y
CONFIG_BUILTIN=y
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2 changes: 1 addition & 1 deletion libs/libc/machine/arm/armv8-m/Kconfig
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Expand Up @@ -7,7 +7,7 @@ if ARCH_ARMV8M

config ARMV8M_STRING_FUNCTION
bool "Enable optimized ARMv8M specific string function"
default n
default y

@xiaoxiang781216 xiaoxiang781216 May 25, 2026 •
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why change the default value? it impacts the binary size on the small chip

@patrickelectric patrickelectric May 25, 2026 •
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It adds 1.2kB in flash. (at least from the test that I did here)
I would believe that small chips could just disable this option, and so having it on by default. This has a terrible performance impact as showed in the commit body and PR body as well.

@xiaoxiang781216 xiaoxiang781216 May 26, 2026

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so, you need update ALL arch from n to y, not only arm.

@patrickelectric patrickelectric May 26, 2026

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I'll wait for Peter comment before proceeding.

depends on ARCH_TOOLCHAIN_GNU
select ARMV8M_MEMCHR
select ARMV8M_MEMCPY
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