86 Architecture

BIOS

• BIOS is firmware embedded on a motherboard that initializes hardware components and prepares the system for booting an operating system.
• A bootloader is a small program that loads the operating system into memory when the computer starts up.

Registers

EIP

EIP (Extended Instruction Pointer) is a 32-bit register in the x86 architecture. It holds the memory address of the next instruction that the CPU will execute.

FSM

The FSM (Flag Status Register) in x86 architecture is a special register that contains flags indicating the status of the CPU after an arithmetic or logical operation.

The main internal bus

The main internal bus in a computer system refers to the set of pathways (wires) used to transfer data, addresses, and control signals between the CPU, memory, and other peripherals.

Special Purpose Registers

Assemble the program

nasm -f elf32 hello.asm -o hello.o

Link the object files

ld -m elf_i386 -s -o hello hello.o

1. nasm -f elf32 hello.asm -o hello.o

- nasm: Assembler for x86 assembly language.
- -f elf32: Specifies the output format. elf32 indicates a 32-bit ELF (Executable and Linkable Format) object file. Since hello.asm is likely a 32-bit assembly program, the elf32 format is appropriate.

In short, this command assembles the hello.asm file into an object file hello.o using the 32-bit ELF format.

2. ld -m elf_i386 -o hello hello.o

ld: The linker command. It links the object files produced by the assembler into an executable file.
-m elf_i386: Specifies the target format for the linker. elf_i386 tells ld to create a 32-bit ELF executable for the i386 architecture.
-o hello: Specifies the name of the final output executable file. In this case, the executable will be named hello.
hello.o: The input object file that was produced in the previous step (hello.o). This file contains the machine code generated from hello.asm.

Syscalls

Standard File Descriptors:

Resources

https://www.linuxjournal.com/article/4048 https://www.youtube.com/watch?v=busHtSyx2-w&list=PLetF-YjXm-sCH6FrTz4AQhfH6INDQvQSn&index=3