What

Pratice assembly language

Steps

# start working environment
docker run -it --rm -v ${PWD}:/my-code johnnyb61820/linux-assembly

#  assemble source code into machine code (object file)
as myexit.s -o results/myexit.o

# link object file to make it executable
ld results/myexit.o -o results/myexit

Register layout

General purpose register

%rax: accumulator (64 bit)
%eax: accumulator (32 bit)
%ax: accumulator (16 bit)
%ah: high byte of %ax
%al: low byte of %ax

%rbx: base (64 bit)
%ebx: base (32 bit)
%bx: base (16 bit)
%bh: high byte of %bx
%bl: low byte of %bx

%rcx: counter (64 bit)
%ecx: counter (32 bit)
%cx: counter (16 bit)
%ch: high byte of %cx
%cl: low byte of %cx

%rdx: data (64 bit)
%edx: data (32 bit)
%dx: data (16 bit)
%dh: high byte of %dx
%dl: low byte of %dx

%rsi: source index
%rdi: destination index
%rbp: base pointer
%rsp: stack pointer

%r8 - %r15

Special-purpose registers

%rip: instruction pointer
%eflags: compare and jump

System call register (in order)

1. %rdi
2. %rsi
3. %rdx
4. %r10
5. %r8
6. %r9

Preservation of Registers during function call

1. %rbp
2. %rbx
3. %r12 through %r15

Input Parameters for function call (in order)

1. %rdi
2. %rsi
3. %rdx
4. %rcx
5. %r8
6. %r9

Jump instruction

• jz: jump if Zero (jump if the zero flag is set to 1)

• jnz: jump if Not Zero (jump if the zero flag is set to 0)

• jc: jump if Carry (jump if the carry flag is set to 1)

• jnc: jump if No Carry (jump if the carry flag is set to 0)

• jo： jump if the overflow flag is set

• jno： jump if overflow flag is not set

• js: jump if the sign flag is set

• jns: jump if the sign flag is set

• je: jump if ARG2 equals ARG1

• jne: jump if ARG2 does not equal ARG1

• ja: jump if ARG2 is above (greater than) ARG1

• jae: jump if ARG2 is above (greater than) or equal to ARG1

• jb: jump if ARG2 is below (less than) than ARG1

• jbe: jump if ARG2 is below (less than) or equal to ARG1