It seems Arm9 requries, but A7 doesn't.
Hi,
to support aligning data allocated on the stack, the stack pointer (SP) is required to be 8-byte aligned on entry to a conforming function.
Please refetr to "ABI for the ARM® Architecture Advisory Note – SP must be 8-byte aligned on entry to AAPCS-conforming functions" (http://infocenter.arm.com/help/topic/com.arm.doc.ihi0046b/IHI0046B_ABI_Advisory_1.pdf).
Best regards,
Yasuhiko Koumoto.