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>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/arm/lib/lib1funcs.S b/arch/arm/lib/lib1funcs.S
index af2267f6a529..9397b2e532af 100644
--- a/arch/arm/lib/lib1funcs.S
+++ b/arch/arm/lib/lib1funcs.S
@@ -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)