gas: too many memory reference

Question

When compiling the following instruction:

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

I got: too many memory reference.

What's wrong with it?

Answer 1

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)

Answer 2

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

Answer 3

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