How setup() Works

• The setup() function is loaded at offset 0x200 of the kernel image file

• Initializes hardware devices and sets up the kernel execution environment

  • But Linux sometimes relies on BIOS for initialization

• Major operations

  • Invokes a BIOS procedure to determine the amount of RAM
  • Initializes keyboard
  • Initializes the graphics adapter
  • Reinitializes the disk controller
  • Checks for buses, bus mice, APM, etc
  • If needed, moves the kernel image to make space for decompression
  • Sets up the Interrupt Descriptor Table (IDT) and a Global Descriptor Table (GDT)
  • Remaps the interrupts (BIOS maps hardware interrupts to the CPU exception range)
  • Switches to protected mode
  • Jumps to startup_32(), which starts the kernel proper