jos/kern/entry.S
Anish Athalye 1a83673424 Lab 1
2018-08-30 15:17:20 -04:00

97 lines
2.7 KiB
ArmAsm

/* See COPYRIGHT for copyright information. */
#include <inc/mmu.h>
#include <inc/memlayout.h>
# Shift Right Logical
#define SRL(val, shamt) (((val) >> (shamt)) & ~(-1 << (32 - (shamt))))
###################################################################
# The kernel (this code) is linked at address ~(KERNBASE + 1 Meg),
# but the bootloader loads it at address ~1 Meg.
#
# RELOC(x) maps a symbol x from its link address to its actual
# location in physical memory (its load address).
###################################################################
#define RELOC(x) ((x) - KERNBASE)
#define MULTIBOOT_HEADER_MAGIC (0x1BADB002)
#define MULTIBOOT_HEADER_FLAGS (0)
#define CHECKSUM (-(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS))
###################################################################
# entry point
###################################################################
.text
# The Multiboot header
.align 4
.long MULTIBOOT_HEADER_MAGIC
.long MULTIBOOT_HEADER_FLAGS
.long CHECKSUM
# '_start' specifies the ELF entry point. Since we haven't set up
# virtual memory when the bootloader enters this code, we need the
# bootloader to jump to the *physical* address of the entry point.
.globl _start
_start = RELOC(entry)
.globl entry
entry:
movw $0x1234,0x472 # warm boot
# We haven't set up virtual memory yet, so we're running from
# the physical address the boot loader loaded the kernel at: 1MB
# (plus a few bytes). However, the C code is linked to run at
# KERNBASE+1MB. Hence, we set up a trivial page directory that
# translates virtual addresses [KERNBASE, KERNBASE+4MB) to
# physical addresses [0, 4MB). This 4MB region will be
# sufficient until we set up our real page table in mem_init
# in lab 2.
# Load the physical address of entry_pgdir into cr3. entry_pgdir
# is defined in entrypgdir.c.
movl $(RELOC(entry_pgdir)), %eax
movl %eax, %cr3
# Turn on paging.
movl %cr0, %eax
orl $(CR0_PE|CR0_PG|CR0_WP), %eax
movl %eax, %cr0
# Now paging is enabled, but we're still running at a low EIP
# (why is this okay?). Jump up above KERNBASE before entering
# C code.
mov $relocated, %eax
jmp *%eax
relocated:
# Clear the frame pointer register (EBP)
# so that once we get into debugging C code,
# stack backtraces will be terminated properly.
movl $0x0,%ebp # nuke frame pointer
# Set the stack pointer
movl $(bootstacktop),%esp
# now to C code
call i386_init
# Should never get here, but in case we do, just spin.
spin: jmp spin
.data
###################################################################
# boot stack
###################################################################
.p2align PGSHIFT # force page alignment
.globl bootstack
bootstack:
.space KSTKSIZE
.globl bootstacktop
bootstacktop: