Assembly x64 Intro - GAS Assembly Issue

movslq %eax,%rbx <=> movsx rbx, eax

40056e: 8b 45 d0 mov -0x30(%rbp),%eax

400571: 48 63 d8 movslq %eax,%rbx

400574: 48 8b 45 f0 mov -0x10(%rbp),%rax

400578: 48 99 cqto

40057a: 48 f7 fb idiv %rbx

40057d: 48 89 45 f0 mov %rax,-0x10(%rbp)

400581: 8b 45 10 mov 0x10(%rbp),%eax

400584: 48 98 cltq

400586: 48 01 45 f0 add %rax,-0x10(%rbp)

movslq %eax,%rbx => 拷贝eax 到 rbx, 并对rbx进行符号扩展

cqto => 符号扩展rax到 rdx:rax

400581: 8b 45 10 mov 0x10(%rbp),%eax

400584: 48 98 cltq

cltq => 提升 eax （int32_t） 到 int64_t