The complete memory addressing mode format in AT&T assembly is:
offset(base, index, width)
So for your case:
offset = 0
base = ebx
index = eax
width = 4
Meaning that the instruction is something like:
eax = *(uint32_t *)((uint8_t *)ebx + eax * 4 + 0)
In a C-like pseudocode.
