asm.S

#include "kernel/modes.h"
#include "kernel/memory.h"

_init_stacks:
    cps     #MODE_IRQ
    ldr     sp, =P_STACK_IRQ

    cps     #MODE_FIQ
    ldr     sp, =P_STACK_FIQ

    cps     #MODE_SYS
    ldr     sp, =P_STACK_SYS

    cps     #MODE_UND
    ldr     sp, =P_STACK_UND

    cps     #MODE_ABT
    ldr     sp, =P_STACK_ABT

    cps     #MODE_SVC
    ldr     sp, =P_STACK_SVC

memory.h

#define P_SYSTEM_STACK_SIZE (1024 * 1024 / 8)
#define P_SYSTEM_STACK_START ((void*) 0x8000000)
#define P_STACK_FIQ (P_SYSTEM_STACK_START - P_SYSTEM_STACK_SIZE * 0)
#define P_STACK_IRQ (P_SYSTEM_STACK_START - P_SYSTEM_STACK_SIZE * 1)
#define P_STACK_SVC (P_SYSTEM_STACK_START - P_SYSTEM_STACK_SIZE * 2)
#define P_STACK_ABT (P_SYSTEM_STACK_START - P_SYSTEM_STACK_SIZE * 3)
#define P_STACK_UND (P_SYSTEM_STACK_START - P_SYSTEM_STACK_SIZE * 4)
#define P_STACK_SYS (P_SYSTEM_STACK_START - P_SYSTEM_STACK_SIZE * 5)