Chapter 3 Machine Level Representation of Programs Flashcards
Assembly code suffix b represents…
C declaration: Char
Intel data type : Byte
Size: 1 byte
Assembly code suffix w represents…
C declaration: short
Intel data type : Word
Size: 2 bytes
Assembly code suffix l represents
C declaration: int or double
Intel data type : Double word(int), Double precision (double)
Size: 4 bytes (int), 8 bytes(double)
Assembly code suffix q represents:
C declaration: long or char*
Intel data type : Quad word
Size: 8 bytes
Assembly code suffix s
C declaration: float
Intel data type : Single precision
Size: 4 bytes
in x86-64, what is the size of pointers
8 bytes
Return register for 64 bit machine
%rax (r for 64)
Return register for 32 bit machine
%eax (e for 32)
Return register for 16 bit machine
%ax
Data movement instruction
mov
$
immediate value
movzb
Move zero extending byte. These instructions have a register or memory location as the source and a register as the destination
movsbw
move sign-extended byte to word (bw can change to bl, wl… meaning from one type to another)
PC
Program Counter
Importance of PC
Holds address of next instruction
What do Condition codes do
Store status information about most recent arithmetic or logical operation
Used for conditional branching
What is Memory
- Byte addressable array
- Code and user data
- Stack to support procedures
Translate to C
movq $0x4,%rax
Immediate value to register
temp = 0x4
Translate to C
movq $-147,(%rax)
Immediate value to memory
*p = -147
Translate to C
movq %rax,%rdx
register to register
temp2 = temp1
Translate to C
movq %rax,(%rdx)
Register to memory
*p = temp
Translate to C
movq (%rax),%rdx
Memory to register
temp = *p
Meaning of the following unary operation
neg
Arithmetic negation
Meaning of the following unary operation
not
Bitwise complement
addq
Dest = Dest + Src
subq
Dest = Dest - Src
imulq
Dest = Dest * Src
salq or shlq
Dest = Dest «_space;Src
sarq
Dest = Dest»_space; Src ARITHMETIC
shrq
Dest = Dest»_space; Src LOGICAL
xorq
Dest = Dest ^ Src
andq
Dest = Dest & Src
orq
Dest = Dest | Src
incq
Dest = Dest + 1
decq
Dest = Dest -1
negq
Dest = -Dest
notq
Dest = ~Dest
Difference between neg and not
NEG changes -1 to 1 because it reverses all the bits and adds 1
NOT changes -1 to 0 because it reverses all the bits only
What is a stack
Data structure where values can be added or deleted according to “last-in, first out” rule
Register to hold location of runtime stack
%rsp
Register to hold location of current code
control (instruction) point
%rip
CF
Carry Flag (for unsigned)
Set if carry out from most significant bit(unsigned overflow)
ZF
Zero flag
Set if t == 0
SF
Sign flag (for signed)
Set if t < 0 (as signed)
OF
Overflow flag(for signed)
Set if two’s complement overflow
cmpq b,a
Is like computing a - b without setting destination
ZF in compare
Set if a == b
SF in compare
Set if (a-b) < 0 (as signed)
testq b,a
Is like computing a&b without setting destination
ZF in test
Set when a&b == 0
SF in test
Set when a&b <0
Translate to C
movl (%rdi, %rsi, 4), %eax
%rdi + 4*%rsi
