Writing a simple Linux Kernel on Armv8 - 6

By ozan ocak on May 26, 2021

aarch64 kernel linux

Interrupts

First we need to implement our vector interrupt table

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#include "entry.h"

.macro kernel_entry
    sub sp, sp, #S_FRAME_SIZE
    stp x0, x1, [sp, #16 * 0]
    stp x2, x3, [sp, #16 * 1]
    stp	x4, x5, [sp, #16 * 2]
	stp	x6, x7, [sp, #16 * 3]
	stp	x8, x9, [sp, #16 * 4]
	stp	x10, x11, [sp, #16 * 5]
	stp	x12, x13, [sp, #16 * 6]
	stp	x14, x15, [sp, #16 * 7]
	stp	x16, x17, [sp, #16 * 8]
	stp	x18, x19, [sp, #16 * 9]
	stp	x20, x21, [sp, #16 * 10]
	stp	x22, x23, [sp, #16 * 11]
	stp	x24, x25, [sp, #16 * 12]
	stp	x26, x27, [sp, #16 * 13]
	stp	x28, x29, [sp, #16 * 14]
	str	x30, [sp, #16 * 15] 
.endm

.macro kernel_exit
    ldp x0, x1, [sp, #16 * 0]
    ldp x2, x3, [sp, #16 * 1]
    ldp	x4, x5, [sp, #16 * 2]
	ldp	x6, x7, [sp, #16 * 3]
	ldp	x8, x9, [sp, #16 * 4]
	ldp	x10, x11, [sp, #16 * 5]
	ldp	x12, x13, [sp, #16 * 6]
	ldp	x14, x15, [sp, #16 * 7]
	ldp	x16, x17, [sp, #16 * 8]
	ldp	x18, x19, [sp, #16 * 9]
	ldp	x20, x21, [sp, #16 * 10]
	ldp	x22, x23, [sp, #16 * 11]
	ldp	x24, x25, [sp, #16 * 12]
	ldp	x26, x27, [sp, #16 * 13]
	ldp	x28, x29, [sp, #16 * 14]
	ldr	x30, [sp, #16 * 15] 
	add	sp, sp, #S_FRAME_SIZE
    eret
.endm

.macro handle_invalid_entry type
	kernel_entry
	mov	x0, #\type
	mrs	x1, esr_el1
	mrs	x2, elr_el1
	bl	show_invalid_entry_message
	b	err_hang
.endm

.macro	ventry	label
.align	7
    b	\label
.endm

//Exception vectors table
.align	11
.globl vectors 
vectors:
	ventry	sync_invalid_el1t			// Synchronous EL1t
	ventry	irq_invalid_el1t			// IRQ EL1t
	ventry	fiq_invalid_el1t			// FIQ EL1t
	ventry	error_invalid_el1t			// Error EL1t

	ventry	sync_invalid_el1h			// Synchronous EL1h
	ventry	handle_el1_irq				// IRQ EL1h
	ventry	fiq_invalid_el1h			// FIQ EL1h
	ventry	error_invalid_el1h			// Error EL1h

	ventry	sync_invalid_el0_64			// Synchronous 64-bit EL0
	ventry	irq_invalid_el0_64			// IRQ 64-bit EL0
	ventry	fiq_invalid_el0_64			// FIQ 64-bit EL0
	ventry	error_invalid_el0_64		// Error 64-bit EL0

	ventry	sync_invalid_el0_32			// Synchronous 32-bit EL0
	ventry	irq_invalid_el0_32			// IRQ 32-bit EL0
	ventry	fiq_invalid_el0_32			// FIQ 32-bit EL0
	ventry	error_invalid_el0_32		// Error 32-bit EL0


sync_invalid_el1t:
	handle_invalid_entry  SYNC_INVALID_EL1t

irq_invalid_el1t:
	handle_invalid_entry  IRQ_INVALID_EL1t

fiq_invalid_el1t:
	handle_invalid_entry  FIQ_INVALID_EL1t

error_invalid_el1t:
	handle_invalid_entry  ERROR_INVALID_EL1t

sync_invalid_el1h:
	handle_invalid_entry  SYNC_INVALID_EL1h

fiq_invalid_el1h:
	handle_invalid_entry  FIQ_INVALID_EL1h

error_invalid_el1h:
	handle_invalid_entry  ERROR_INVALID_EL1h

sync_invalid_el0_64:
	handle_invalid_entry  SYNC_INVALID_EL0_64

irq_invalid_el0_64:
	handle_invalid_entry  IRQ_INVALID_EL0_64

fiq_invalid_el0_64:
	handle_invalid_entry  FIQ_INVALID_EL0_64

error_invalid_el0_64:
	handle_invalid_entry  ERROR_INVALID_EL0_64

sync_invalid_el0_32:
	handle_invalid_entry  SYNC_INVALID_EL0_32

irq_invalid_el0_32:
	handle_invalid_entry  IRQ_INVALID_EL0_32

fiq_invalid_el0_32:
	handle_invalid_entry  FIQ_INVALID_EL0_32

error_invalid_el0_32:
	handle_invalid_entry  ERROR_INVALID_EL0_32

handle_el1_irq:
	kernel_entry 
	bl	handle_irq
	kernel_exit 

.globl err_hang
err_hang: b err_hang

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#pragma once

//D1.10.2
#define SYNC_INVALID_EL1t		0 
#define IRQ_INVALID_EL1t		1 
#define FIQ_INVALID_EL1t		2 
#define ERROR_INVALID_EL1t		3 

#define SYNC_INVALID_EL1h		4 
#define IRQ_INVALID_EL1h		5 
#define FIQ_INVALID_EL1h		6 
#define ERROR_INVALID_EL1h		7 

#define SYNC_INVALID_EL0_64	    8 
#define IRQ_INVALID_EL0_64	    9 
#define FIQ_INVALID_EL0_64		10 
#define ERROR_INVALID_EL0_64	11 

#define SYNC_INVALID_EL0_32		12 
#define IRQ_INVALID_EL0_32		13 
#define FIQ_INVALID_EL0_32		14 
#define ERROR_INVALID_EL0_32	15 

//stack frame size
#define S_FRAME_SIZE			256

then definations of interrupt methods which are enable,disable and initialize

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#pragma once

void irq_init_vectors();
void irq_enable();
void irq_disable();

void enable_interrupt_controller();

then finally in kernel.c

we need include

#include "irq.h"

then in kernel_main() function, after initializing uart

irq_init_vectors();
enable_interrupt_controller();
irq_enable();