test$ cat test.asm

        xchg bx, dx
        xchg cx, dx
test$ nasm test.asm -l /dev/stderr
     1
     2 00000000 87DA                            xchg bx, dx
     3 00000002 87CA                            xchg cx, dx
test$ ndisasm test
00000000  87DA              xchg bx,dx
00000002  87CA              xchg cx,dx
test$ ~/proj/nasmtest/patch/nasm test.asm -l /dev/stderr
     1
     2 00000000 87D3                            xchg bx, dx
     3 00000002 87D1                            xchg cx, dx
test$ ~/proj/nasmtest/patch/ndisasm test
00000000  87D3              xchg bx,dx
00000002  87D1              xchg cx,dx
test$ ndisasm test
00000000  87D3              xchg dx,bx
00000002  87D1              xchg dx,cx
test$