interrupt_vector_table:
  // ARM core does the following on interrupt:
  // 1) save cpsr into spsr
  // 2) set mode bits in current cpsr
  // 3) disable further interrupts of lower/same priority
  // 4) store return address in lr
  // 5) set pc to correct vector table entry below
  ldr pc, _reset_asm_handler                 // priority: 1st
  ldr pc, _undefined_instruction_asm_handler // priority: 6th
  ldr pc, _swi_asm_handler                   // priority: 6th
  ldr pc, _prefetch_abort_asm_handler        // priority: 5th
  ldr pc, _data_abort_asm_handler            // priority: 2nd
  ldr pc, _reset_asm_handler                 // priority: undefined
  ldr pc, _irq_asm_handler                   // priority: 4th
  ldr pc, _fiq_asm_handler                   // priority: 3rd

/**
 * SOFT vector table that is loaded by install_vector_table ABOVE
 * interrupt_vector_table
 */
// to make sure the addresses are aligned this must follow the
// actual vector table above!
_reset_asm_handler:                 .word reset_asm_handler
_undefined_instruction_asm_handler: .word undefined_instruction_asm_handler
_swi_asm_handler:                   .word swi_asm_handler
_prefetch_abort_asm_handler:        .word prefetch_abort_asm_handler
_data_abort_asm_handler:            .word data_abort_asm_handler
_irq_asm_handler:                   .word irq_asm_handler
_fiq_asm_handler:                   .word fiq_asm_handler


/**
 * called to install the vector table at address 0x0
 */
.global install_interrupt_table
install_interrupt_table:
  copy the vector table into multiple registers
  copy the values of the vector table into the actual memory location
  do the same for soft vector table
  move lr into pc

irq_asm_handler:
  push shit
  bl irq_c_handler
  pop shit
  cpsr/spsr somewhere inbetween


  //Everything restored
  movs pc, lr       @ returns and sets flag like that thing you showed me



reset_asm_handler:
  b _start // just reset the kernel


/************************************************************
 * If you fall into one of these handlers something bad is
 * happening. bkpt will drop back into gdb so you can debug.
 ************************************************************/
undefined_instruction_asm_handler:
  bkpt

prefetch_abort_asm_handler:
  bkpt

data_abort_asm_handler:
  bkpt

fiq_asm_handler:
  bkpt


/************************************************************/
/* Initializes cpsr for user mode and jumps to user program */
/************************************************************/
.global enter_user_mode
enter_user_mode:
  push {r0-r12}
  mrs r0, cpsr
  and r0, #0xffffff00
  add r0, #0xD0
  msr cpsr, r0
  ldr sp, =__user_stack_top
  bl __user_program