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| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2015-12-12 02:49:21 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2015-12-17 11:29:01 +0100 |
| commit | 42f25bddd0a226d2431e057b9e01c5cc61067e12 (patch) | |
| tree | 33e3bf9c4669caba06f72303e5d333e2acd15e78 /arch/arm/Kconfig | |
| parent | ARM: 8476/1: VDSO: use PTR_ERR_OR_ZERO for vma check (diff) | |
| download | linux-42f25bddd0a226d2431e057b9e01c5cc61067e12.tar.xz linux-42f25bddd0a226d2431e057b9e01c5cc61067e12.zip | |
ARM: 8477/1: runtime patch udiv/sdiv instructions into __aeabi_{u}idiv()
The ARM compiler inserts calls to __aeabi_idiv() and
__aeabi_uidiv() when it needs to perform division on signed and
unsigned integers. If a processor has support for the sdiv and
udiv instructions, the kernel may overwrite the beginning of those
functions with those instructions and a "bx lr" to get better
performance.
To ensure that those functions are aligned to a 32-bit word for easier
patching (which might not always be the case in Thumb mode) and that
the two patched instructions end up in the same cache line, a 8-byte
alignment is enforced when ARM_PATCH_IDIV is selected.
This was heavily inspired by a previous patch from Stephen Boyd.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/Kconfig')
| -rw-r--r-- | arch/arm/Kconfig | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 9f1eeb2e7d75..6e644fd68ad2 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -1603,6 +1603,24 @@ config THUMB2_AVOID_R_ARM_THM_JUMP11 config ARM_ASM_UNIFIED bool +config ARM_PATCH_IDIV + bool "Runtime patch udiv/sdiv instructions into __aeabi_{u}idiv()" + depends on CPU_32v7 && !XIP_KERNEL + default y + help + The ARM compiler inserts calls to __aeabi_idiv() and + __aeabi_uidiv() when it needs to perform division on signed + and unsigned integers. Some v7 CPUs have support for the sdiv + and udiv instructions that can be used to implement those + functions. + + Enabling this option allows the kernel to modify itself to + replace the first two instructions of these library functions + with the sdiv or udiv plus "bx lr" instructions when the CPU + it is running on supports them. Typically this will be faster + and less power intensive than running the original library + code to do integer division. + config AEABI bool "Use the ARM EABI to compile the kernel" help |