What does (register1, register2, 4) mean in AT&T assembly?
For example:
cmp %eax, (%esi, %ebx, 4)
Carl Norum
The complete AT&T base/index register syntax is:
offset(base, index, multiplier)
Your offset field is 0, so you just have the (base, index, multiplier) part. In your case, you're comparing the contents of the eax register to the 32-bit value located at esi + (ebx * 4).
In the Intel syntax you might be more familiar with, this would be written as:
cmp [ebx*4 + esi], eax
来源：https://stackoverflow.com/questions/18650093/what-does-a-comma-in-a-parenthesis-mean-in-the-att-syntax-for-x86-assembly