add lab answers

labcodes_answer/lab2_result/kern/init/entry.S

@@ -0,0 +1,49 @@
+#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)
+

labcodes_answer/lab2_result/kern/init/init.c

@@ -0,0 +1,104 @@
+#include <defs.h>
+#include <stdio.h>
+#include <string.h>
+#include <console.h>
+#include <kdebug.h>
+#include <picirq.h>
+#include <trap.h>
+#include <clock.h>
+#include <intr.h>
+#include <pmm.h>
+
+int kern_init(void) __attribute__((noreturn));
+
+static void lab1_switch_test(void);
+
+int
+kern_init(void) {
+    extern char edata[], end[];
+    memset(edata, 0, end - edata);
+
+    cons_init();                // init the console
+
+    const char *message = "(THU.CST) os is loading ...";
+    cprintf("%s\n\n", message);
+
+    print_kerninfo();
+
+    grade_backtrace();
+
+    pmm_init();                 // init physical memory management
+
+    pic_init();                 // init interrupt controller
+    idt_init();                 // init interrupt descriptor table
+
+    clock_init();               // init clock interrupt
+    intr_enable();              // enable irq interrupt
+
+    //LAB1: CAHLLENGE 1 If you try to do it, uncomment lab1_switch_test()
+    // user/kernel mode switch test
+    //lab1_switch_test();
+
+    /* do nothing */
+    while (1);
+}
+
+void __attribute__((noinline))
+grade_backtrace2(int arg0, int arg1, int arg2, int arg3) {
+    mon_backtrace(0, NULL, NULL);
+}
+
+void __attribute__((noinline))
+grade_backtrace1(int arg0, int arg1) {
+    grade_backtrace2(arg0, (int)&arg0, arg1, (int)&arg1);
+}
+
+void __attribute__((noinline))
+grade_backtrace0(int arg0, int arg1, int arg2) {
+    grade_backtrace1(arg0, arg2);
+}
+
+void
+grade_backtrace(void) {
+    grade_backtrace0(0, (int)kern_init, 0xffff0000);
+}
+
+static void
+lab1_print_cur_status(void) {
+    static int round = 0;
+    uint16_t reg1, reg2, reg3, reg4;
+    asm volatile (
+            "mov %%cs, %0;"
+            "mov %%ds, %1;"
+            "mov %%es, %2;"
+            "mov %%ss, %3;"
+            : "=m"(reg1), "=m"(reg2), "=m"(reg3), "=m"(reg4));
+    cprintf("%d: @ring %d\n", round, reg1 & 3);
+    cprintf("%d:  cs = %x\n", round, reg1);
+    cprintf("%d:  ds = %x\n", round, reg2);
+    cprintf("%d:  es = %x\n", round, reg3);
+    cprintf("%d:  ss = %x\n", round, reg4);
+    round ++;
+}
+
+static void
+lab1_switch_to_user(void) {
+    //LAB1 CHALLENGE 1 : TODO
+}
+
+static void
+lab1_switch_to_kernel(void) {
+    //LAB1 CHALLENGE 1 :  TODO
+}
+
+static void
+lab1_switch_test(void) {
+    lab1_print_cur_status();
+    cprintf("+++ switch to  user  mode +++\n");
+    lab1_switch_to_user();
+    lab1_print_cur_status();
+    cprintf("+++ switch to kernel mode +++\n");
+    lab1_switch_to_kernel();
+    lab1_print_cur_status();
+}
+