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ARM: 8477/1: runtime patch udiv/sdiv instructions into __aeabi_{u}idiv()

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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>
This commit is contained in:
Nicolas Pitre
2015-12-12 02:49:21 +01:00
committed by Russell King
parent 38fc2f6c98
commit 42f25bddd0
3 changed files with 93 additions and 0 deletions
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8
arch/arm/lib/lib1funcs.S
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@@ -205,6 +205,10 @@ Boston, MA 02111-1307, USA. */
.endm
#ifdef CONFIG_ARM_PATCH_IDIV
.align 3
#endif
ENTRY(__udivsi3)
ENTRY(__aeabi_uidiv)
UNWIND(.fnstart)
@@ -253,6 +257,10 @@ UNWIND(.fnstart)
UNWIND(.fnend)
ENDPROC(__umodsi3)
#ifdef CONFIG_ARM_PATCH_IDIV
.align 3
#endif
ENTRY(__divsi3)
ENTRY(__aeabi_idiv)
UNWIND(.fnstart)