Write the LEGv8 assembly code to implement the following C code:

 lock(lk); shvar=max(shvar,x); unlock(lk); 

Assume that the address of the lk variable is in X0, the address of the shvar variable is in X1, and the value of variable x is in X2. Your critical section should not contain any function calls. Use LDXR/STXR instructions to implement the lock() operation, the unlock() operation is simply an ordinary store instruction.