update for mooc OS labs

homework/hw2.txt

@@ -1,88 +0,0 @@
-第二次作业
-
-OS concept ver7课本第8章、第九章的习题：
-
-8.3 Given ?ve memory partitions of 100 KB, 500 KB, 200 KB, 300 KB,and
-600 KB (in order), how would each of the ?rst-?t, best-?t, and worst-?t
-algorithms place processes of 212 KB, 417 KB, 112 KB, and 426 KB (in
-order)?Which algorithm makes the most ef?cient use of memory?
-
-8.4 Most systems allow programs to allocate more memory to its address
-space during execution.Data allocated in the heap segments of programs
-is an example of such allocated memory. What is required to support
-dynamic memory allocation in the following schemes:
-a. contiguous-memory allocation
-b. pure segmentation
-c. pure paging
-
-8.12 Consider the following segment table:
-Segment Base Length
-0 219 600
-1 2300 14
-2 90 100
-3 1327 580
-4 1952 96
-What are the physical addresses for the following logical addresses?
-a. 0,430
-b. 1,10
-c. 2,500
-d. 3,400
-e. 4,112
-
-9.5 Assume we have a demand-paged memory. The page table is held in
-registers. It takes 8 milliseconds to service a page fault if an empty page
-is available or the replaced page is not modi?ed, and 20 milliseconds if
-the replaced page is modi?ed. Memory access time is 100 nanoseconds.
-Assume that the page to be replaced is modi?ed 70 percent of the time.
-What is the maximum acceptable page-fault rate for an effective access
-time of no more than 200 nanoseconds?
-
-
-9.13 A page-replacement algorithm should minimize the number of page
-faults. We can do this minimization by distributing heavily used pages
-evenly over all of memory, rather than having them compete for a small
-number of page frames.We can associatewith each page frame a counter
-of the number of pages that are associated with that frame. Then, to
-replace a page, we search for the page frame with the smallest counter.
-a. De?ne a page-replacement algorithmusing this basic idea. Specif-
-ically address the problems of (1) what the initial value of the
-counters is, (2) when counters are increased, (3) when counters
-are decreased, and (4) how the page to be replaced is selected.
-b. Howmany page faults occur for your algorithmfor the following
-reference string, for four page frames?
-1, 2, 3, 4, 5, 3, 4, 1, 6, 7, 8, 7, 8, 9, 7, 8, 9, 5, 4, 5, 4, 2.
-c. What is the minimumnumber of page faults for an optimal page-
-replacement strategy for the reference string in part b with four
-page frames?
-
-1. 请证明LRU算法不会存在belady现象。
-
-2. 请证明或详细说明FIFO/CLOCK/Enhanced CLOCK是否有belady现象？
-
-
-实验相关
-------------------
-
-1 lab1的proj1的ucore的代码中是否有使用了绝对地址（编译期间指定的绝对内存地址）？
-
-2 lab2 的ucore的小os的load addr和link addr分别是多少?
-
-3 ucore用了哪个数据结构来管理空闲内存，位于内存什么地方，占多少空间？
-
-4 请考虑在ucore中实现second chance/enhanced clock页替换算法的设计思路。主要描述如何利用相关x86相关硬件、如何设计数据结构，大致要实现哪些函数，函数的大致功能和整体流程。 
-
-5 实现enhanced clock algorithm中，
-IF before clock sweep: (used,dirty) = (1,1), THEN after clock sweep: (used, dirty)=(0,1).
-如果把上述转换改为：
-IF before clock sweep: (used,dirty) = (1,1), THEN after clock sweep: (used, dirty)=(1,0).
-是否可行？
-
-6 在clock算法实现中，pte中的uesd bit位是否可以让os来设置1 or 0 ? 为什么？
-
-7 在enhanced clock算法中的dirty bit位是否可以让os来设置1 or 0 ? 为什么？
-
-8 如果在ucore中实现精确的LRU算法，如何设计？需要硬件和OS分别完成什么事情？
-
-9 如果在ucore中实现工作集页替换算法和缺页频率替换算法，如何设计？
-
-

homework/hw3.txt

@@ -1,15 +0,0 @@
-#第三次作业  process/thread
-1. process与thread在实现上和执行上有何区别？
-2. process与program（程序)的区别与联系是什么？
-3. process的执行状态转换图是啥？各个状态的含义是什么？
-4. thread的实现方式有几种？这几种有何区别？
-5. fork和exec的执行逻辑（大致要完成的事情）是什么？
-6. 父进程与子进程之间在内容上有何差异？在执行上有何差异？
-7. 父进程fork完子进程后，这两个进程在执行的过程中是否有先后顺序？
-8. 进程/线程上下文切换的执行逻辑是什么？二者有无区别？如有，区别是啥？
-9. 为何vfork机制在有了Copy on Write (简称COW)技术后意义变得不大了？
-10. 如何在ucore中实现COW技术？
-11. 进程有几个栈？栈的作用是什么？
-12. exec的内核实现中，如何返回到新的进程的入口点，并正确执行用户态的进程？
-13. 内核线程和用户进程的mm结构有何区别？为什么？
-14. 如何在ucore中实现可在用户态执行的线程？

labcodes/lab1/Makefile

@@ -207,6 +207,8 @@ TARGETS: $(TARGETS)
 .DEFAULT_GOAL := TARGETS
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG)
+	$(V)$(QEMU) -monitor stdio -hda $< -serial null
 qemu: $(UCOREIMG)
 	$(V)$(QEMU) -parallel stdio -hda $< -serial null
 

labcodes/lab2/Makefile

@@ -231,6 +231,8 @@ targets: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG)
 
 .PHONY: qemu qemu-nox gdb debug debug-mon debug-nox
+qemu-mon: targets
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: targets
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes/lab3/Makefile

@@ -225,6 +225,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes/lab4/Makefile

@@ -229,6 +229,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes/lab5/Makefile

@@ -268,6 +268,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes/lab6/Makefile

@@ -268,6 +268,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes/lab7/Makefile

@@ -268,6 +268,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG)  $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes/lab8/Makefile

@@ -308,6 +308,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback -drive file=$(SFSIMG),media=disk,cache=writeback 
 
 .PHONY: qemu qemu-nox debug debug-nox monitor
+qemu-mon: $(UCOREIMG) $(SWAPIMG) $(SFSIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG) $(SFSIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes_answer/lab1_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-elf-qemu > /dev/null; \
 	then echo 'i386-elf-qemu'; exit; \
 	else \
@@ -197,6 +197,17 @@ TARGETS: $(TARGETS)
 .DEFAULT_GOAL := TARGETS
 
 .PHONY: qemu qemu-nox debug debug-nox
+lab1-mon: $(UCOREIMG)
+	$(V)$(TERMINAL) -e "$(QEMU) -S -s -d in_asm -D $(BINDIR)/q.log -monitor stdio -hda $< -serial null"
+	$(V)sleep 2
+	$(V)$(TERMINAL) -e "gdb -q -x tools/lab1init"
+debug-mon: $(UCOREIMG)
+#	$(V)$(QEMU) -S -s -monitor stdio -hda $< -serial null &
+	$(V)$(TERMINAL) -e "$(QEMU) -S -s -monitor stdio -hda $< -serial null"
+	$(V)sleep 2
+	$(V)$(TERMINAL) -e "gdb -q -x tools/moninit"
+qemu-mon: $(UCOREIMG)
+	$(V)$(QEMU) -monitor stdio -hda $< -serial null
 qemu: $(UCOREIMG)
 	$(V)$(QEMU) -parallel stdio -hda $< -serial null
 

labcodes_answer/lab1_result/boot/bootasm.S

@@ -27,20 +27,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
     # Switch from real to protected mode, using a bootstrap GDT
     # and segment translation that makes virtual addresses

labcodes_answer/lab1_result/kern/init/init.c

@@ -8,9 +8,9 @@
 #include <clock.h>
 #include <intr.h>
 #include <pmm.h>
-
+#include <kmonitor.h>
 int kern_init(void) __attribute__((noreturn));
-
+void grade_backtrace(void);
 static void lab1_switch_test(void);
 
 int
@@ -37,7 +37,7 @@ kern_init(void) {
 
     //LAB1: CAHLLENGE 1 If you try to do it, uncomment lab1_switch_test()
     // user/kernel mode switch test
-    //lab1_switch_test();
+    lab1_switch_test();
 
     /* do nothing */
     while (1);
@@ -84,11 +84,24 @@ lab1_print_cur_status(void) {
 static void
 lab1_switch_to_user(void) {
     //LAB1 CHALLENGE 1 : TODO
+	asm volatile (
+	    "sub $0x8, %%esp \n"
+	    "int %0 \n"
+	    "movl %%ebp, %%esp"
+	    : 
+	    : "i"(T_SWITCH_TOU)
+	);
 }
 
 static void
 lab1_switch_to_kernel(void) {
     //LAB1 CHALLENGE 1 :  TODO
+	asm volatile (
+	    "int %0 \n"
+	    "movl %%ebp, %%esp \n"
+	    : 
+	    : "i"(T_SWITCH_TOK)
+	);
 }
 
 static void

labcodes_answer/lab1_result/kern/trap/trap.c

@@ -8,7 +8,7 @@
 #include <assert.h>
 #include <console.h>
 #include <kdebug.h>
-
+#include <string.h>
 #define TICK_NUM 100
 
 static void print_ticks() {
@@ -51,6 +51,9 @@ idt_init(void) {
     for (i = 0; i < sizeof(idt) / sizeof(struct gatedesc); i ++) {
         SETGATE(idt[i], 0, GD_KTEXT, __vectors[i], DPL_KERNEL);
     }
+	// set for switch from user to kernel
+    SETGATE(idt[T_SWITCH_TOK], 0, GD_KTEXT, __vectors[T_SWITCH_TOK], DPL_USER);
+	// load the IDT
     lidt(&idt_pd);
 }
 
@@ -140,6 +143,9 @@ print_regs(struct pushregs *regs) {
     cprintf("  eax  0x%08x\n", regs->reg_eax);
 }
 
+/* temporary trapframe or pointer to trapframe */
+struct trapframe switchk2u, *switchu2k;
+
 /* trap_dispatch - dispatch based on what type of trap occurred */
 static void
 trap_dispatch(struct trapframe *tf) {
@@ -168,8 +174,30 @@ trap_dispatch(struct trapframe *tf) {
         break;
     //LAB1 CHALLENGE 1 : YOUR CODE you should modify below codes.
     case T_SWITCH_TOU:
+        if (tf->tf_cs != USER_CS) {
+            switchk2u = *tf;
+            switchk2u.tf_cs = USER_CS;
+            switchk2u.tf_ds = switchk2u.tf_es = switchk2u.tf_ss = USER_DS;
+            switchk2u.tf_esp = (uint32_t)tf + sizeof(struct trapframe) - 8;
+		
+            // set eflags, make sure ucore can use io under user mode.
+            // if CPL > IOPL, then cpu will generate a general protection.
+            switchk2u.tf_eflags |= FL_IOPL_MASK;
+		
+            // set temporary stack
+            // then iret will jump to the right stack
+            *((uint32_t *)tf - 1) = (uint32_t)&switchk2u;
+        }
+        break;
     case T_SWITCH_TOK:
-        panic("T_SWITCH_** ??\n");
+        if (tf->tf_cs != KERNEL_CS) {
+            tf->tf_cs = KERNEL_CS;
+            tf->tf_ds = tf->tf_es = KERNEL_DS;
+            tf->tf_eflags &= ~FL_IOPL_MASK;
+            switchu2k = (struct trapframe *)(tf->tf_esp - (sizeof(struct trapframe) - 8));
+            memmove(switchu2k, tf, sizeof(struct trapframe) - 8);
+            *((uint32_t *)tf - 1) = (uint32_t)switchu2k;
+        }
         break;
     case IRQ_OFFSET + IRQ_IDE1:
     case IRQ_OFFSET + IRQ_IDE2:

labcodes_answer/lab1_result/report.txt

@@ -0,0 +1,469 @@
+Lab1 report
+[练习1]
+
+[练习1.1] 操作系统镜像文件 ucore.img 是如何一步一步生成的?(需要比较详细地解释 Makefile 中
+每一条相关命令和命令参数的含义,以及说明命令导致的结果)
+
+bin/ucore.img
+| 生成ucore.img的相关代码为
+| $(UCOREIMG): $(kernel) $(bootblock)
+|	$(V)dd if=/dev/zero of=$@ count=10000
+|	$(V)dd if=$(bootblock) of=$@ conv=notrunc
+|	$(V)dd if=$(kernel) of=$@ seek=1 conv=notrunc
+|
+| 为了生成ucore.img，首先需要生成bootblock、kernel
+|
+|>	bin/bootblock
+|	| 生成bootblock的相关代码为
+|	| $(bootblock): $(call toobj,$(bootfiles)) | $(call totarget,sign)
+|	|	@echo + ld $@
+|	|	$(V)$(LD) $(LDFLAGS) -N -e start -Ttext 0x7C00 $^ \
+|	|		-o $(call toobj,bootblock)
+|	|	@$(OBJDUMP) -S $(call objfile,bootblock) > \
+|	|		$(call asmfile,bootblock)
+|	|	@$(OBJCOPY) -S -O binary $(call objfile,bootblock) \
+|	|		$(call outfile,bootblock)
+|	|	@$(call totarget,sign) $(call outfile,bootblock) $(bootblock)
+|	|
+|	| 为了生成bootblock，首先需要生成bootasm.o、bootmain.o、sign
+|	|
+|	|>	obj/boot/bootasm.o, obj/boot/bootmain.o
+|	|	| 生成bootasm.o,bootmain.o的相关makefile代码为
+|	|	| bootfiles = $(call listf_cc,boot) 
+|	|	| $(foreach f,$(bootfiles),$(call cc_compile,$(f),$(CC),\
+|	|	|	$(CFLAGS) -Os -nostdinc))
+|	|	| 实际代码由宏批量生成
+|	|	| 
+|	|	| 生成bootasm.o需要bootasm.S
+|	|	| 实际命令为
+|	|	| gcc -Iboot/ -fno-builtin -Wall -ggdb -m32 -gstabs \
+|	|	| 	-nostdinc  -fno-stack-protector -Ilibs/ -Os -nostdinc \
+|	|	| 	-c boot/bootasm.S -o obj/boot/bootasm.o
+|	|	| 其中关键的参数为
+|	|	| 	-ggdb  生成可供gdb使用的调试信息
+|	|	|	-m32  生成适用于32位环境的代码
+|	|	| 	-gstabs  生成stabs格式的调试信息
+|	|	| 	-nostdinc  不使用标准库
+|	|	|	-fno-stack-protector  不生成用于检测缓冲区溢出的代码
+|	|	| 	-Os  为减小代码大小而进行优化
+|	|	| 	-I<dir>  添加搜索头文件的路径
+|	|	| 
+|	|	| 生成bootmain.o需要bootmain.c
+|	|	| 实际命令为
+|	|	| gcc -Iboot/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc \
+|	|	| 	-fno-stack-protector -Ilibs/ -Os -nostdinc \
+|	|	| 	-c boot/bootmain.c -o obj/boot/bootmain.o
+|	|	| 新出现的关键参数有
+|	|	| 	-fno-builtin  除非用__builtin_前缀，
+|	|	|	              否则不进行builtin函数的优化
+|	|
+|	|>	bin/sign
+|	|	| 生成sign工具的makefile代码为
+|	|	| $(call add_files_host,tools/sign.c,sign,sign)
+|	|	| $(call create_target_host,sign,sign)
+|	|	| 
+|	|	| 实际命令为
+|	|	| gcc -Itools/ -g -Wall -O2 -c tools/sign.c \
+|	|	| 	-o obj/sign/tools/sign.o
+|	|	| gcc -g -Wall -O2 obj/sign/tools/sign.o -o bin/sign
+|	|
+|	| 首先生成bootblock.o
+|	| ld -m    elf_i386 -nostdlib -N -e start -Ttext 0x7C00 \
+|	|	obj/boot/bootasm.o obj/boot/bootmain.o -o obj/bootblock.o
+|	| 其中关键的参数为
+|	|	-m <emulation>  模拟为i386上的连接器
+|	|	-nostdlib  不使用标准库
+|	|	-N  设置代码段和数据段均可读写
+|	|	-e <entry>  指定入口
+|	|	-Ttext  制定代码段开始位置
+|	|
+|	| 拷贝二进制代码bootblock.o到bootblock.out
+|	| objcopy -S -O binary obj/bootblock.o obj/bootblock.out
+|	| 其中关键的参数为
+|	|	-S  移除所有符号和重定位信息
+|	|	-O <bfdname>  指定输出格式
+|	|
+|	| 使用sign工具处理bootblock.out，生成bootblock
+|	| bin/sign obj/bootblock.out bin/bootblock
+|
+|>	bin/kernel
+|	| 生成kernel的相关代码为
+|	| $(kernel): tools/kernel.ld
+|	| $(kernel): $(KOBJS)
+|	| 	@echo + ld $@
+|	| 	$(V)$(LD) $(LDFLAGS) -T tools/kernel.ld -o $@ $(KOBJS)
+|	| 	@$(OBJDUMP) -S $@ > $(call asmfile,kernel)
+|	| 	@$(OBJDUMP) -t $@ | $(SED) '1,/SYMBOL TABLE/d; s/ .* / /; \
+|	| 		/^$$/d' > $(call symfile,kernel)
+|	| 
+|	| 为了生成kernel，首先需要 kernel.ld init.o readline.o stdio.o kdebug.o
+|	|	kmonitor.o panic.o clock.o console.o intr.o picirq.o trap.o
+|	|	trapentry.o vectors.o pmm.o  printfmt.o string.o
+|	| kernel.ld已存在
+|	|
+|	|>	obj/kern/*/*.o 
+|	|	| 生成这些.o文件的相关makefile代码为
+|	|	| $(call add_files_cc,$(call listf_cc,$(KSRCDIR)),kernel,\
+|	|	|	$(KCFLAGS))
+|	|	| 这些.o生成方式和参数均类似，仅举init.o为例，其余不赘述
+|	|>	obj/kern/init/init.o
+|	|	| 编译需要init.c
+|	|	| 实际命令为
+|	|	|	gcc -Ikern/init/ -fno-builtin -Wall -ggdb -m32 \
+|	|	|		-gstabs -nostdinc  -fno-stack-protector \
+|	|	|		-Ilibs/ -Ikern/debug/ -Ikern/driver/ \
+|	|	|		-Ikern/trap/ -Ikern/mm/ -c kern/init/init.c \
+|	|	|		-o obj/kern/init/init.o
+|	| 
+|	| 生成kernel时，makefile的几条指令中有@前缀的都不必需
+|	| 必需的命令只有
+|	| ld -m    elf_i386 -nostdlib -T tools/kernel.ld -o bin/kernel \
+|	| 	obj/kern/init/init.o obj/kern/libs/readline.o \
+|	| 	obj/kern/libs/stdio.o obj/kern/debug/kdebug.o \
+|	| 	obj/kern/debug/kmonitor.o obj/kern/debug/panic.o \
+|	| 	obj/kern/driver/clock.o obj/kern/driver/console.o \
+|	| 	obj/kern/driver/intr.o obj/kern/driver/picirq.o \
+|	| 	obj/kern/trap/trap.o obj/kern/trap/trapentry.o \
+|	| 	obj/kern/trap/vectors.o obj/kern/mm/pmm.o \
+|	| 	obj/libs/printfmt.o obj/libs/string.o
+|	| 其中新出现的关键参数为
+|	|	-T <scriptfile>  让连接器使用指定的脚本
+|
+| 生成一个有10000个块的文件，每个块默认512字节，用0填充
+| dd if=/dev/zero of=bin/ucore.img count=10000
+|
+| 把bootblock中的内容写到第一个块
+| dd if=bin/bootblock of=bin/ucore.img conv=notrunc
+|
+| 从第二个块开始写kernel中的内容
+| dd if=bin/kernel of=bin/ucore.img seek=1 conv=notrunc
+
+[练习1.2] 一个被系统认为是符合规范的硬盘主引导扇区的特征是什么?
+
+从sign.c的代码来看，一个磁盘主引导扇区只有512字节。且
+第510个（倒数第二个）字节是0x55，
+第511个（倒数第一个）字节是0xAA。
+
+
+
+[练习2]
+
+[练习2.1] 从 CPU 加电后执行的第一条指令开始,单步跟踪 BIOS 的执行。
+
+通过改写Makefile文件  ()
+	debug: $(UCOREIMG)
+		$(V)$(TERMINAL) -e "$(QEMU) -S -s -d in_asm -D $(BINDIR)/q.log -parallel stdio -hda $< -serial null"
+		$(V)sleep 2
+		$(V)$(TERMINAL) -e "gdb -q -tui -x tools/gdbinit"
+在调用qemu时增加-d in_asm -D q.log参数，便可以将运行的汇编指令保存在q.log中。
+为防止qemu在gdb连接后立即开始执行，删除了tools/gdbinit中的"continue"行。
+
+[练习2.2] 在初始化位置0x7c00 设置实地址断点,测试断点正常。
+
+在tools/gdbinit结尾加上
+    set architecture i8086  //设置当前调试的CPU是8086
+	b *0x7c00  //在0x7c00处设置断点。此地址是bootloader入口点地址，可看boot/bootasm.S的start地址处
+	c          //continue简称，表示继续执行
+	x /2i $pc  //显示当前eip处的汇编指令
+	set architecture i386  //设置当前调试的CPU是80386
+	
+运行"make debug"便可得到
+	Breakpoint 2, 0x00007c00 in ?? ()
+	=> 0x7c00:      cli    
+	   0x7c01:      cld    
+	   0x7c02:      xor    %eax,%eax
+	   0x7c04:      mov    %eax,%ds
+	   0x7c06:      mov    %eax,%es
+	   0x7c08:      mov    %eax,%ss 
+	   0x7c0a:      in     $0x64,%al
+	   0x7c0c:      test   $0x2,%al
+	   0x7c0e:      jne    0x7c0a
+	   0x7c10:      mov    $0xd1,%al
+
+[练习2.3] 在调用qemu 时增加-d in_asm -D q.log 参数，便可以将运行的汇编指令保存在q.log 中。
+将执行的汇编代码与bootasm.S 和 bootblock.asm 进行比较，看看二者是否一致。
+
+在tools/gdbinit结尾加上
+	b *0x7c00
+	c
+	x /10i $pc
+便可以在q.log中读到"call bootmain"前执行的命令
+	----------------
+	IN: 
+	0x00007c00:  cli    
+	
+	----------------
+	IN: 
+	0x00007c01:  cld    
+	0x00007c02:  xor    %ax,%ax
+	0x00007c04:  mov    %ax,%ds
+	0x00007c06:  mov    %ax,%es
+	0x00007c08:  mov    %ax,%ss
+	
+	----------------
+	IN: 
+	0x00007c0a:  in     $0x64,%al
+	
+	----------------
+	IN: 
+	0x00007c0c:  test   $0x2,%al
+	0x00007c0e:  jne    0x7c0a
+	
+	----------------
+	IN: 
+	0x00007c10:  mov    $0xd1,%al
+	0x00007c12:  out    %al,$0x64
+	0x00007c14:  in     $0x64,%al
+	0x00007c16:  test   $0x2,%al
+	0x00007c18:  jne    0x7c14
+	
+	----------------
+	IN: 
+	0x00007c1a:  mov    $0xdf,%al
+	0x00007c1c:  out    %al,$0x60
+	0x00007c1e:  lgdtw  0x7c6c
+	0x00007c23:  mov    %cr0,%eax
+	0x00007c26:  or     $0x1,%eax
+	0x00007c2a:  mov    %eax,%cr0
+	
+	----------------
+	IN: 
+	0x00007c2d:  ljmp   $0x8,$0x7c32
+	
+	----------------
+	IN: 
+	0x00007c32:  mov    $0x10,%ax
+	0x00007c36:  mov    %eax,%ds
+	
+	----------------
+	IN: 
+	0x00007c38:  mov    %eax,%es
+	
+	----------------
+	IN: 
+	0x00007c3a:  mov    %eax,%fs
+	0x00007c3c:  mov    %eax,%gs
+	0x00007c3e:  mov    %eax,%ss
+	
+	----------------
+	IN: 
+	0x00007c40:  mov    $0x0,%ebp
+	
+	----------------
+	IN: 
+	0x00007c45:  mov    $0x7c00,%esp
+	0x00007c4a:  call   0x7d0d
+	
+	----------------
+	IN: 
+	0x00007d0d:  push   %ebp
+其与bootasm.S和bootblock.asm中的代码相同。
+
+[练习3] 分析bootloader 进入保护模式的过程。
+
+从%cs=0 $pc=0x7c00，进入后
+
+首先清理环境：包括将flag置0和将段寄存器置0
+	.code16
+	    cli
+	    cld
+	    xorw %ax, %ax
+	    movw %ax, %ds
+	    movw %ax, %es
+	    movw %ax, %ss
+
+开启A20：通过将键盘控制器上的A20线置于高电位，全部32条地址线可用，
+可以访问4G的内存空间。
+	seta20.1:               # 等待8042键盘控制器不忙
+	    inb $0x64, %al      # 
+	    testb $0x2, %al     #
+	    jnz seta20.1        #
+	
+	    movb $0xd1, %al     # 发送写8042输出端口的指令
+	    outb %al, $0x64     #
+	
+	seta20.1:               # 等待8042键盘控制器不忙
+	    inb $0x64, %al      # 
+	    testb $0x2, %al     #
+	    jnz seta20.1        #
+	
+	    movb $0xdf, %al     # 打开A20
+	    outb %al, $0x60     # 
+
+初始化GDT表：一个简单的GDT表和其描述符已经静态储存在引导区中，载入即可
+	    lgdt gdtdesc
+
+进入保护模式：通过将cr0寄存器PE位置1便开启了保护模式
+	    movl %cr0, %eax
+	    orl $CR0_PE_ON, %eax
+	    movl %eax, %cr0
+
+通过长跳转更新cs的基地址
+	    ljmp $PROT_MODE_CSEG, $protcseg
+	.code32
+	protcseg:
+
+设置段寄存器，并建立堆栈
+	    movw $PROT_MODE_DSEG, %ax
+	    movw %ax, %ds
+	    movw %ax, %es
+	    movw %ax, %fs
+	    movw %ax, %gs
+	    movw %ax, %ss
+	    movl $0x0, %ebp
+	    movl $start, %esp
+
+转到保护模式完成，进入boot主方法
+	    call bootmain
+
+
+
+[练习4] ：分析bootloader加载ELF格式的OS的过程。
+
+首先看readsect函数，
+readsect从设备的第secno扇区读取数据到dst位置
+	static void
+	readsect(void *dst, uint32_t secno) {
+	    waitdisk();
+	
+	    outb(0x1F2, 1);                         // 设置读取扇区的数目为1
+	    outb(0x1F3, secno & 0xFF);
+	    outb(0x1F4, (secno >> 8) & 0xFF);
+	    outb(0x1F5, (secno >> 16) & 0xFF);
+	    outb(0x1F6, ((secno >> 24) & 0xF) | 0xE0);
+	        // 上面四条指令联合制定了扇区号
+	        // 在这4个字节线联合构成的32位参数中
+	        //   29-31位强制设为1
+	        //   28位(=0)表示访问"Disk 0"
+	        //   0-27位是28位的偏移量
+	    outb(0x1F7, 0x20);                      // 0x20命令，读取扇区
+	
+	    waitdisk();
+
+	    insl(0x1F0, dst, SECTSIZE / 4);         // 读取到dst位置，
+	                                            // 幻数4因为这里以DW为单位
+	}
+
+readseg简单包装了readsect，可以从设备读取任意长度的内容。
+	static void
+	readseg(uintptr_t va, uint32_t count, uint32_t offset) {
+	    uintptr_t end_va = va + count;
+	
+	    va -= offset % SECTSIZE;
+	
+	    uint32_t secno = (offset / SECTSIZE) + 1; 
+	    // 加1因为0扇区被引导占用
+	    // ELF文件从1扇区开始
+	
+	    for (; va < end_va; va += SECTSIZE, secno ++) {
+	        readsect((void *)va, secno);
+	    }
+	}
+
+
+在bootmain函数中，
+	void
+	bootmain(void) {
+	    // 首先读取ELF的头部
+	    readseg((uintptr_t)ELFHDR, SECTSIZE * 8, 0);
+	
+	    // 通过储存在头部的幻数判断是否是合法的ELF文件
+	    if (ELFHDR->e_magic != ELF_MAGIC) {
+	        goto bad;
+	    }
+	
+	    struct proghdr *ph, *eph;
+	
+	    // ELF头部有描述ELF文件应加载到内存什么位置的描述表，
+	    // 先将描述表的头地址存在ph
+	    ph = (struct proghdr *)((uintptr_t)ELFHDR + ELFHDR->e_phoff);
+	    eph = ph + ELFHDR->e_phnum;
+	
+	    // 按照描述表将ELF文件中数据载入内存
+	    for (; ph < eph; ph ++) {
+	        readseg(ph->p_va & 0xFFFFFF, ph->p_memsz, ph->p_offset);
+	    }
+	    // ELF文件0x1000位置后面的0xd1ec比特被载入内存0x00100000
+	    // ELF文件0xf000位置后面的0x1d20比特被载入内存0x0010e000
+
+	    // 根据ELF头部储存的入口信息，找到内核的入口
+	    ((void (*)(void))(ELFHDR->e_entry & 0xFFFFFF))();
+	
+	bad:
+	    outw(0x8A00, 0x8A00);
+	    outw(0x8A00, 0x8E00);
+	    while (1);
+	}
+
+
+
+[练习5] 实现函数调用堆栈跟踪函数 
+
+ss:ebp指向的堆栈位置储存着caller的ebp，以此为线索可以得到所有使用堆栈的函数ebp。
+ss:ebp+4指向caller调用时的eip，ss:ebp+8等是（可能的）参数。
+
+输出中，堆栈最深一层为
+	ebp:0x00007bf8 eip:0x00007d68 \
+		args:0x00000000 0x00000000 0x00000000 0x00007c4f
+	    <unknow>: -- 0x00007d67 --
+其对应的是第一个使用堆栈的函数，bootmain.c中的bootmain。
+bootloader设置的堆栈从0x7c00开始，使用"call bootmain"转入bootmain函数。
+call指令压栈，所以bootmain中ebp为0x7bf8。
+
+
+
+[练习6] 完善中断初始化和处理
+
+[练习6.1] 中断向量表中一个表项占多少字节？其中哪几位代表中断处理代码的入口？
+
+中断向量表一个表项占用8字节，其中2-3字节是段选择子，0-1字节和6-7字节拼成位移，
+两者联合便是中断处理程序的入口地址。
+
+[练习6.2] 请编程完善kern/trap/trap.c中对中断向量表进行初始化的函数idt_init。
+见代码
+
+[练习6.3] 请编程完善trap.c中的中断处理函数trap，在对时钟中断进行处理的部分填写trap函数
+见代码
+
+
+[练习7]  增加syscall功能，即增加一用户态函数（可执行一特定系统调用：获得时钟计数值），
+当内核初始完毕后，可从内核态返回到用户态的函数，而用户态的函数又通过系统调用得到内核态的服务
+
+在idt_init中，将用户态调用SWITCH_TOK中断的权限打开。
+	SETGATE(idt[T_SWITCH_TOK], 1, KERNEL_CS, __vectors[T_SWITCH_TOK], 3);
+
+在trap_dispatch中，将iret时会从堆栈弹出的段寄存器进行修改
+	对TO User
+	    tf->tf_cs = USER_CS;
+	    tf->tf_ds = USER_DS;
+	    tf->tf_es = USER_DS;
+	    tf->tf_ss = USER_DS;
+	对TO Kernel
+	    tf->tf_cs = KERNEL_CS;
+	    tf->tf_ds = KERNEL_DS;
+	    tf->tf_es = KERNEL_DS;
+
+在lab1_switch_to_user中，调用T_SWITCH_TOU中断。
+注意从中断返回时，会多pop两位，并用这两位的值更新ss,sp，损坏堆栈。
+所以要先把栈压两位，并在从中断返回后修复esp。
+	asm volatile (
+	    "sub $0x8, %%esp \n"
+	    "int %0 \n"
+	    "movl %%ebp, %%esp"
+	    : 
+	    : "i"(T_SWITCH_TOU)
+	);
+
+在lab1_switch_to_kernel中，调用T_SWITCH_TOK中断。
+注意从中断返回时，esp仍在TSS指示的堆栈中。所以要在从中断返回后修复esp。
+	asm volatile (
+	    "int %0 \n"
+	    "movl %%ebp, %%esp \n"
+	    : 
+	    : "i"(T_SWITCH_TOK)
+	);
+
+但这样不能正常输出文本。根据提示，在trap_dispatch中转User态时，将调用io所需权限降低。
+	tf->tf_eflags |= 0x3000;
+
+

labcodes_answer/lab1_result/tools/function.mk

@@ -70,7 +70,7 @@ endef
 # finish all
 define do_finish_all
 ALLDEPS = $$(ALLOBJS:.o=.d)
-$$(sort $$(dir $$(ALLOBJS)) $(BINDIR) $(OBJDIR)):
+$$(sort $$(dir $$(ALLOBJS)) $(BINDIR)$(SLASH) $(OBJDIR)$(SLASH)):
 	@$(MKDIR) $$@
 endef
 

labcodes_answer/lab1_result/tools/lab1init

@@ -0,0 +1,6 @@
+file bin/kernel
+target remote :1234
+set architecture i8086
+b *0x7c00
+continue
+x /2i $pc

labcodes_answer/lab1_result/tools/moninit

@@ -0,0 +1,3 @@
+file bin/kernel
+target remote :1234
+break kern_init

labcodes_answer/lab2_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-ucore-elf-qemu > /dev/null; \
 	then echo 'i386-ucore-elf-qemu'; exit; \
 	else \
@@ -208,6 +208,8 @@ targets: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG)
 
 .PHONY: qemu qemu-nox gdb debug debug-mon debug-nox
+qemu-mon: targets
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: targets
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes_answer/lab3_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-ucore-elf-qemu > /dev/null; \
 	then echo 'i386-ucore-elf-qemu'; exit; \
 	else \
@@ -216,6 +216,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes_answer/lab4_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-ucore-elf-qemu > /dev/null; \
 	then echo 'i386-ucore-elf-qemu'; exit; \
 	else \
@@ -220,6 +220,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes_answer/lab5_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-ucore-elf-qemu > /dev/null; \
 	then echo 'i386-ucore-elf-qemu'; exit; \
 	else \
@@ -259,6 +259,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes_answer/lab6_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-ucore-elf-qemu > /dev/null; \
 	then echo 'i386-ucore-elf-qemu'; exit; \
 	else \
@@ -259,6 +259,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes_answer/lab7_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-ucore-elf-qemu > /dev/null; \
 	then echo 'i386-ucore-elf-qemu'; exit; \
 	else \
@@ -259,6 +259,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback
 
 .PHONY: qemu qemu-nox debug debug-nox
+qemu-mon: $(UCOREIMG) $(SWAPIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null
 

labcodes_answer/lab8_result/Makefile

@@ -23,8 +23,8 @@ endif
 
 # try to infer the correct QEMU
 ifndef QEMU
-QEMU := $(shell if which qemu > /dev/null; \
+QEMU := $(shell if which qemu-system-i386 > /dev/null; \
-	then echo 'qemu'; exit; \
+	then echo 'qemu-system-i386'; exit; \
 	elif which i386-ucore-elf-qemu > /dev/null; \
 	then echo 'i386-ucore-elf-qemu'; exit; \
 	else \
@@ -296,6 +296,8 @@ TARGETS: $(TARGETS)
 QEMUOPTS = -hda $(UCOREIMG) -drive file=$(SWAPIMG),media=disk,cache=writeback -drive file=$(SFSIMG),media=disk,cache=writeback 
 
 .PHONY: qemu qemu-nox debug debug-nox monitor
+qemu-mon: $(UCOREIMG) $(SWAPIMG) $(SFSIMG)
+	$(V)$(QEMU) -monitor stdio $(QEMUOPTS) -serial null
 qemu: $(UCOREIMG) $(SWAPIMG) $(SFSIMG)
 	$(V)$(QEMU) -parallel stdio $(QEMUOPTS) -serial null