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>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 9f1eeb2..6e644fd 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1603,6 +1603,24 @@
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
