gas: too many memory reference

The number before the parenthesis is a byte offset (which causes a memory reference to occur), and you cannot have two of them with movl. You need to move the value temporarily to a register first.

movl 4(%ebp), %ecx
movl %ecx, 8(%ebp)

It is not a legal instruction. For most instructions that reference memory you must move it to/from a register.

movl doesn't to memory-memory moves, you have to go by way of a register (thus with two movl instructions).