mutex in armv8

Finally I am working on armv8 soc now. At the very beginning I need a mutex, which is essential for multiple core processors. The old strex/lderx on longer available, now we have ldxr/stxr instead

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dht0008a/ch01s03s02.html


get_lock PROC
mov w1, #0x1
try_loop
ldaxr w2, [x0]
cbnz w2, try_loop
stxr w2, w1, [x0]
cbnz w2, try_loop
ret
ENDP


free_lock PROC
mov w1, #0x0
stlr w1, [x0]
ret
ENDP

try_lock PROC
mov w1, #0x1
ldaxr w2, [x0]
cbnz w2, exit
stxr w2, w1, [x0]
exit
mov w0, w2
ret
ENDP