Why would one use “movl $1,

Question

As the title states, why would one use \"movl $1, %eax\" as opposed to, say, \"movb $1, %eax\", I was told that movl would zero out the high order bits of %eax, but isn\'t %eax

Answer 1

On a 32 bit machine, %eax is a 4 byte (32 bit) register. movl will write into all 4 bytes. In your example, it'll zero out the upper 3 bytes, and put 1 in the lowest byte. The movb will just change the low order byte.