《操作系统》的实验代码。
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#include <mmu.h>
#include <memlayout.h>
#define REALLOC(x) (x - KERNBASE)
.text
.globl kern_entry
kern_entry:
# reload temperate gdt (second time) to remap all physical memory
# virtual_addr 0~4G=linear_addr&physical_addr -KERNBASE~4G-KERNBASE
lgdt REALLOC(__gdtdesc)
movl $KERNEL_DS, %eax
movw %ax, %ds
movw %ax, %es
movw %ax, %ss
ljmp $KERNEL_CS, $relocated
relocated:
# set ebp, esp
movl $0x0, %ebp
# the kernel stack region is from bootstack -- bootstacktop,
# the kernel stack size is KSTACKSIZE (8KB)defined in memlayout.h
movl $bootstacktop, %esp
# now kernel stack is ready , call the first C function
call kern_init
# should never get here
spin:
jmp spin
.data
.align PGSIZE
.globl bootstack
bootstack:
.space KSTACKSIZE
.globl bootstacktop
bootstacktop:
.align 4
__gdt:
SEG_NULL
SEG_ASM(STA_X | STA_R, - KERNBASE, 0xFFFFFFFF) # code segment
SEG_ASM(STA_W, - KERNBASE, 0xFFFFFFFF) # data segment
__gdtdesc:
.word 0x17 # sizeof(__gdt) - 1
.long REALLOC(__gdt)