What does 0x4 do in “movl $0x2d, 0x4(%esp)”?

Question

I am looking into assembly code generated by GCC. But I don\'t understand:

movl $0x2d, 0x4(%esp)

In the second operand, what does 0x4

Answer 1

GCC assembly operands follow a byte (b), word (w), long (l) and so on such as :

movb
movw
movl

Registers are prefixed with a percentage sign (%).

Constants are prefixed with a dollar sign ($).

In the above example in your question that means the 4th offset from the stack pointer (esp).

Hope this helps, Best regards, Tom.