data transfer instruction
| instruction | Effect | describe |
|---|---|---|
| MOV S,D | D<—S | send |
| movb | transmit bytes | |
| movw | transfer word | |
| movl | send double word | |
| movq | send four characters | |
| movabsq I,R | R<—I | send absolute quads |
Simple data transfer instructions, note that both operands cannot be memory
| instruction | Effect | describe |
|---|---|---|
| MOVZ S,R | R<—zero extension (S) | Delivered with zero extension |
| movzbw | transfer zero-extended byte to word | |
| movzbl | transfer zero-extended byte to double word | |
| movzwl | transfer zero-extended word to double word | |
| movzbq | Transfer zero-extended bytes to quadwords | |
| movzwq | Transfer zero-extended word to quadword |
Zero-extended data transfer instruction. These instructions take a register or memory address as source and register as destination
| instruction | Effect | describe |
|---|---|---|
| MOVS S,R | R<—sign extension (S) | transfer sign-extended bytes |
| movsbw | transfer sign-extended bytes to words | |
| movsbl | transfer sign-extended byte to double word | |
| movswl | transfer sign-extended word to double word | |
| movsbq | Transfer sign-extended bytes to quadwords | |
| movswq | transfer sign-extended word to quadword | |
| movslq | transfer sign-extended doubleword to quadword | |
| cltq | %rax<—sign extension (%eax) | Extend %eax sign to %rax |
Sign-extended data transfer instruction. The MOVS instruction takes a register or memory address as the source and the register as the destination. The cltq instruction only acts on registers %eax and %rax
stack operation
In x86-64, the stack grows downward. The
register %rsp is used to operate on the stack
| instruction | Effect | describe |
|---|---|---|
| push S | R[%rsp]<—R[%rsp]-8; | push quadword onto stack |
| M[R[%rsp]]<—S | ||
| popq D | D<—M[R[%rsp]]; | pop the quadword off the stack |
| R[%rsp]<—R[%rsp]+8 |
Pushing to the stack is to first move the stack pointer down by 8 bits, and then assign a value
- The behavior of pushq %rbp is equivalent to the following two instructions:
subq $8, %rsp Decrement stack pointer
movq %rbp, (%rsp) Store %rbp on stack- popq %rax is equivalent to the following two instructions
movq (%rsp), %rax Read %rax from stack
addq $8, %rsp Increment stack pointer