Issue passing array to FORTRAN subroutine

New to Julia
2 
julia> x = [1.0, 2.0]
2-element Array{Float64,1}:
 1.0
 2.0

julia> y = [0.0, 0.0]
2-element Array{Float64,1}:
 0.0
 0.0

julia> ccall( (:add_, "./test.so"), Cvoid, (Ref{Float64}, Ref{Float64}), x, y )
   1.0000000000000000        2.0000000000000000     
   2.0000000000000000        4.0000000000000000     

julia> x
2-element Array{Float64,1}:
 1.0
 2.0

julia> y
2-element Array{Float64,1}:
 2.0
 4.0
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