MOV
The MOV instruction class has four primary variants: movb, movw, movl, and movq. There also exist zero extension and sign extension variations in the forms of MOVS and MOVZ.
| Instruction | Operands | Effect | Description |
|---|---|---|---|
mov[bwlq] | S, D | D ← S | Move byte/word/double word/quad word |
movabsq | I, R | R ← I | Move quad word |
movzb[wlq] | S, R | R ← ZE(S) | Move zero-extended byte |
movzw[lq] | S, R | R ← ZE(S) | Move zero-extended word |
movsb[wlq] | S, R | R ← SE(S) | Move sign-extended byte |
movsw[lq] | S, R | R ← SE(S) | Move sign-extended word |
movslq | S, R | R ← SE(S) | Move sign-extended double word |
cltq | %rax ← SE(%eax) | Sign-extend %eax to %rax |
Notice there is no movzlq instruction. movl covers this functionality since, by convention, instructions moving double words into a 64-bit register automatically zeroes out the upper 32 bits.
PUSH and POP
| Instruction | Operands | Effect | Description |
|---|---|---|---|
pushq | S | R[%rsp] ← R[%rsp] - 8 M[R[%rsp]] ← S | Push quad word |
popq | D | D ← M[R[%rsp]] R[%rsp] ← R[%rsp] + 8 | Pop quad word |
In x86 processors, the stack grows downward, with the “top” of the stack corresponding to lower addresses.