Accessing information

Operand forms

Operand Forms .

Immediate: constant values.

Example: $0x1F

Register: denotes the contents of a register

use r_a to denote an arbitrary register a and indicate its value with the reference R[r_a]

Memory reference:

Access some memory location according to a computed address (effective address)
M_b[Addr] - a reference to the b-byte value stored in the memory starting at address Addr.
Imm(r_b,r_i,s) => Effective Address = Imm + R[r_b] + R[r_i]*s
- Immediate offset Imm
- A base register r_b (must be 64-bit registers)
- An index register r_i (must be 64-bit registers)
- A scale factor s (must be 1,2,4 or 8),

Example

Registers contains these addresses:

Register	Value
%rax	0x100
%rcx	0x1
%rdx	0x3

These address contains these hex value:

Address	Value
0x100	0xFF
0x104	0xAB
0x108	0x13
0x10C	0x11

Then we have:

Operand	Value	Comment
%rax	0x100	Register
0x104	0xAB	Absolute Address
$0x108	0x108	Immediate
(%rax)	0xFF	Address 0x100
4(%rax)	0xAB	Address 0x104
9(%rax,%rdx)	0x11	Address 0x10C
260(%rcx, %rdx)	0x13	Address 0x108
0xFC(,%rcx,4)	0xFF	Address 0x100
(%rax,%rdx,4)	0x11	Address 0x10C

Data movement instructions

Note:

All move instruction cannot have both operands refer to memory locations
(‘b’,‘w’,‘l’,‘q’) must match the size of the register

Move

Instruction	Effect	Description
movb S, D	D `<-` S	Move byte
movw S, D	D `<-` S	Move word
movl S, D	D `<-` S	Move double word
movq S, D	D `<-` S	Move quad word
movabsq I, R	R `<-` I	Move absolute squad word

Source can be: immediate, stored in a register, or stored in memory.
Destination can be: register or memory address
Example:

movl $0x4050,%eax Immediate--Register, 4 bytes
movw %bp,%sp Register--Register, 2 bytes
movb (%rdi,%rcx),%al Memory--Register, 1 byte
movb $-17,(%esp) Immediate--Memory, 1 byte
movq %rax,-12(%rbp) Register--Memory, 8 bytes

Move with zero-extending

Copy from a source (immediate, register or memory address) to a register destination, fill out the remaining bytes of the destination with zeros

Instruction	Effect	Description
movzbw S, R	R `<-` S	Move zero-extended byte to word
movzbl S, R	R `<-` S	Move zero-extended byte to double word (long)
movzbq S, R	R `<-` S	Move zero-extended byte to quad word
movzwl S, R	R `<-` S	Move zero-extended word to double word
movzwq S, R	R `<-` I	Move zero-extended word to quad word

Move with sign-extending

Copy from a source (immediate, register or memory address) to a register destination, fill out the remaining bytes of the destination with sign extension.

Instruction	Effect	Description
movsbw S, R	R `<-` SignExtend(S)	Move sign-extended byte to word
movsbl S, R	R `<-` SignExtend(S)	Move sign-extended byte to double word (long)
movsbq S, R	R `<-` SignExtend(S)	Move sign-extended byte to quad word
movswl S, R	R `<-` SignExtend(S)	Move sign-extended word to double word
movswq S, R	R `<-` SignExtend(S)	Move sign-extended word to quad word
movslq S,R	R `<-` SignExtend(S)	Move sign-extended double word to quad word

Pushing and Popping Stack Data

Stack Operations