SP will point to a invalid addr at some time in kernel such as checking stack overflow, and system will crash if fiq-debugger trigger at this time. To solve it, we allocate a separate stack for fiq-debugger, and point SP at the stack before return to kernel. Change-Id: I1175ba032292d072fe2e4ae828d28313646091a7 Signed-off-by: XiaoDong Huang <derrick.huang@rock-chips.com>