mips-linux-gun-as and mips-linux-gnu-ld compile mips failed

1. I use the mips-linux-gnu-as and mips-linux-gun-ld compile the mips assembly code! The code is here!

.data    message: .asciiz "Hi, everybody.\nMy name is Alchemist.\n".text    main:        jal displayMessage        addi $s0, $zero, 5        li $v0, 1        add $a0, $zero, $s0        syscall    # Tell the program that the program is done    li $v0, 10    syscall    displayMessage:        li $v0, 4        la $a0, message        syscall        jr $ra

2.Then i compile the mips asseebe on ubuntu 18.04 TLS!This is my error:

mips-linux-gnu-ld: warning: cannot find entry symbol __start; defaulting to 00000000004000f0

3.How can i due to this error?Thanks!!