Operating System (1) : Bootloader, Interrupt and Device Driver
May 11, 2016
启动操作系统的bootloader，了解操作系统启动前的状态和要做的准备工作，了解运行操作系统的硬件支持，操作系统如何加载到内存中，理解两类中断—“外设中断”，“陷阱中断”
概要
- 基于分段机制的存储管理
- 设备管理的基本概念
- PC启动bootloader的过程
- bootloader的文件组成
- 编译运行bootloader的过程
- 调试bootloader的方法
- 在汇编级了解栈的结构和处理过程
- 中断处理机制
- 通过串口/并口/CGA输出字符的方法
project /
|-- boot
| |-- asm.h
| |-- bootasm.S
| `-- bootmain.c
|-- libs
| |-- types.h
| `-- x86.h
|-- Makefile
`-- tools
|-- function.mk
`-- sign.c
3 directories, 8 files理解通过make生成执行文件的过程
1.操作系统镜像文件ucore.img的生成过程
moocos-> make V=
+ cc kern/init/init.c
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
kern/init/init.c:95:1: warning: ‘lab1_switch_test’ defined but not used [-Wunused-function]
lab1_switch_test(void) {
^
+ cc kern/libs/readline.c
gcc -Ikern/libs/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/libs/readline.c -o obj/kern/libs/readline.o
+ cc kern/libs/stdio.c
gcc -Ikern/libs/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/libs/stdio.c -o obj/kern/libs/stdio.o
+ cc kern/debug/kdebug.c
gcc -Ikern/debug/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/debug/kdebug.c -o obj/kern/debug/kdebug.o
kern/debug/kdebug.c:251:1: warning: ‘read_eip’ defined but not used [-Wunused-function]
read_eip(void) {
^
+ cc kern/debug/kmonitor.c
gcc -Ikern/debug/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/debug/kmonitor.c -o obj/kern/debug/kmonitor.o
+ cc kern/debug/panic.c
gcc -Ikern/debug/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/debug/panic.c -o obj/kern/debug/panic.o
+ cc kern/driver/clock.c
gcc -Ikern/driver/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/driver/clock.c -o obj/kern/driver/clock.o
+ cc kern/driver/console.c
gcc -Ikern/driver/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/driver/console.c -o obj/kern/driver/console.o
+ cc kern/driver/intr.c
gcc -Ikern/driver/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/driver/intr.c -o obj/kern/driver/intr.o
+ cc kern/driver/picirq.c
gcc -Ikern/driver/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/driver/picirq.c -o obj/kern/driver/picirq.o
+ cc kern/trap/trap.c
gcc -Ikern/trap/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/trap/trap.c -o obj/kern/trap/trap.o
kern/trap/trap.c:14:13: warning: ‘print_ticks’ defined but not used [-Wunused-function]
static void print_ticks() {
^
kern/trap/trap.c:30:26: warning: ‘idt_pd’ defined but not used [-Wunused-variable]
static struct pseudodesc idt_pd = {
^
+ cc kern/trap/trapentry.S
gcc -Ikern/trap/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/trap/trapentry.S -o obj/kern/trap/trapentry.o
+ cc kern/trap/vectors.S
gcc -Ikern/trap/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/trap/vectors.S -o obj/kern/trap/vectors.o
+ cc kern/mm/pmm.c
gcc -Ikern/mm/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Ikern/debug/ -Ikern/driver/ -Ikern/trap/ -Ikern/mm/ -c kern/mm/pmm.c -o obj/kern/mm/pmm.o
+ cc libs/printfmt.c
gcc -Ilibs/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -c libs/printfmt.c -o obj/libs/printfmt.o
+ cc libs/string.c
gcc -Ilibs/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -c libs/string.c -o obj/libs/string.o用 gcc 生成 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
+ ld bin/kernel
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用 .o 文件链接生成 bin/kern
+ cc boot/bootasm.S
gcc -Iboot/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Os -nostdinc -c boot/bootasm.S -o obj/boot/bootasm.o
+ cc boot/bootmain.c
gcc -Iboot/ -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc -fno-stack-protector -Ilibs/ -Os -nostdinc -c boot/bootmain.c -o obj/boot/bootmain.o用 gcc 生成 bootasm.o, bootmain.o
+ cc tools/sign.c
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生成 bin/sign
+ ld bin/bootblock
ld -m elf_i386 -nostdlib -N -e start -Ttext 0x7C00 obj/boot/bootasm.o obj/boot/bootmain.o -o obj/bootblock.o
'obj/bootblock.out' size: 472 bytes
build 512 bytes boot sector: 'bin/bootblock' success!
dd if=/dev/zero of=bin/ucore.img count=10000
10000+0 records in
10000+0 records out
5120000 bytes (5.1 MB) copied, 0.109049 s, 47.0 MB/s
dd if=bin/bootblock of=bin/ucore.img conv=notrunc
1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.000198834 s, 2.6 MB/s
dd if=bin/kernel of=bin/ucore.img seek=1 conv=notrunc
138+1 records in
138+1 records out
70775 bytes (71 kB) copied, 0.000586356 s, 121 MB/s最后生成 ucore.img
2.一个被系统认为是符合规范的硬盘主引导扇区的特征
buf[510] = 0x55;
buf[511] = 0xAA;
FILE *ofp = fopen(argv[2], "wb+");
size = fwrite(buf, 1, 512, ofp);
if (size != 512) {
fprintf(stderr, "write '%s' error, size is %d.\n", argv[2], size);
return -1;
}扇区大小为512字节，510字节处为0x55、511字节处为0xAA作为标志
使用qemu执行并调试lab1中的软件
1. 从CPU加电后执行的第一条指令开始，单步跟踪BIOS的执行。
(gdb) x /2i 0xffff0
0xffff0: ljmp $0xf000,$0xe05b
0xffff5: xor %dh,0x322f
(gdb) i r
eax 0x0 0
ecx 0x0 0
edx 0x663 1635
ebx 0x0 0
esp 0x0 0x0
ebp 0x0 0x0
esi 0x0 0
edi 0x0 0
eip 0xfff0 0xfff0
eflags 0x2 [ ]
cs 0xf000 61440
ss 0x0 0
ds 0x0 0
es 0x0 0
fs 0x0 0
gs 0x0 02.在初始化位置0x7c00设置实地址断点,测试断点正常
(gdb) b *0x7c00
Breakpoint 1 at 0x7c00
(gdb) continue
Continuing.
=> 0x7c00: cli
Breakpoint 1, 0x00007c00 in ?? ()3.从0x7c00开始跟踪代码运行,将单步跟踪反汇编得到的代码与bootasm.S和 bootblock.asm进行比较
(gdb) x /6i $pc
=> 0x7c00: cli
0x7c01: cld
0x7c02: xor %ax,%ax
0x7c04: mov %ax,%ds
0x7c06: mov %ax,%es
0x7c08: mov %ax,%ssboottasm.S 中
.globl start
start:
.code16 # Assemble for 16-bit mode
cli # Disable interrupts
cld # String operations increment
# Set up the important data segment registers (DS, ES, SS).
xorw %ax, %ax # Segment number zero
movw %ax, %ds # -> Data Segment
movw %ax, %es # -> Extra Segment
movw %ax, %ss # -> Stack Segment4.对于bootloader或内核中的代码位置，设置断点并进行测试
修改 tools/gdbinit 为
file obj/bootblock.o
target remote :1234
break bootmain
continuemake debug
0x0000fff0 in ?? ()
Breakpoint 1 at 0x7cd1: file boot/bootmain.c, line 87.
Breakpoint 1, bootmain () at boot/bootmain.c:87gdb
│85 /* bootmain - the entry of bootloader */ │
│86 void │
B+>│87 bootmain(void) { │
│88 // read the 1st page off disk │
│89 readseg((uintptr_t)ELFHDR, SECTSIZE * 8, 0); │分析bootloader进入保护模式的过程
为何开启A20，以及如何开启A20
在 boot/bootasm.S 中
# Enable A20:
# For backwards compatibility with the earliest PCs, physical
# 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(8042 input buffer empty).
testb $0x2, %al
jnz seta20.1
movb $0xd1, %al # 0xd1 -> port 0x64
outb %al, $0x64 # 0xd1 means: write data to 8042's P2 port
seta20.2:
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 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1循环查看64端口的值，不小于2时向64端口输出0xd1、向60端口输出0xdf
初始化GDT表
在 boot/bootasm.S 中
lgdt gdtdesc
# Bootstrap GDT
.p2align 2 # force 4 byte alignment
gdt:
SEG_NULLASM # null seg
SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg for bootloader and kernel
SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg for bootloader and kernel
gdtdesc:
.word 0x17 # sizeof(gdt) - 1
.long gdt # address gdt对GDT表进行了初始化
如何进入保护模式
在 boot/bootasm.S 中
movl %cr0, %eax
orl $CR0_PE_ON, %eax
movl %eax, %cr0
# Jump to next instruction, but in 32-bit code segment.
# Switches processor into 32-bit mode.
ljmp $PROT_MODE_CSEG, $protcseg其中
.set CR0_PE_ON, 0x1把 cr0 最后一位置为1，然后跳转保护模式代码段
分析bootloader加载ELF格式的OS的过程
bootloader如何读取硬盘扇区的？
在 boot/bootmain.c 中
static void
readsect(void *dst, uint32_t secno) {
// wait for disk to be ready
waitdisk();
outb(0x1F2, 1); // count = 1
outb(0x1F3, secno & 0xFF);
outb(0x1F4, (secno >> 8) & 0xFF);
outb(0x1F5, (secno >> 16) & 0xFF);
outb(0x1F6, ((secno >> 24) & 0xF) | 0xE0);
outb(0x1F7, 0x20); // cmd 0x20 - read sectors
// wait for disk to be ready
waitdisk();
// read a sector
insl(0x1F0, dst, SECTSIZE / 4);
}其中 waitdisk 函数等待磁盘准备好
static void
waitdisk(void) {
while ((inb(0x1F7) & 0xC0) != 0x40)
/* do nothing */;
}之后发出读取扇区的命令，再调用 waitdisk 函数等待磁盘。之后调用 insl 函数把磁盘扇区数据读到指定内存
static inline void
insl(uint32_t port, void *addr, int cnt) {
asm volatile (
"cld;"
"repne; insl;"
: "=D" (addr), "=c" (cnt)
: "d" (port), "0" (addr), "1" (cnt)
: "memory", "cc");
}bootloader是如何加载ELF格式的OS
在 boot/bootmain.c 中
void
bootmain(void) {
// read the 1st page off disk
readseg((uintptr_t)ELFHDR, SECTSIZE * 8, 0); //读取 elfhdr
// is this a valid ELF?
if (ELFHDR->e_magic != ELF_MAGIC) { //elfhdr 的 e_magic 不为 ELF_MAGIC 时进入 bad 循环
goto bad;
}
struct proghdr *ph, *eph;
// load each program segment (ignores ph flags)
ph = (struct proghdr *)((uintptr_t)ELFHDR + ELFHDR->e_phoff);
eph = ph + ELFHDR->e_phnum;
for (; ph < eph; ph ++) {
readseg(ph->p_va & 0xFFFFFF, ph->p_memsz, ph->p_offset); //加载每一个程序段
}
// call the entry point from the ELF header
// note: does not return
((void (*)(void))(ELFHDR->e_entry & 0xFFFFFF))(); //调用入口地址
bad:
outw(0x8A00, 0x8A00);
outw(0x8A00, 0x8E00);
/* do nothing */
while (1);
}实现函数调用堆栈跟踪函数
make 的时候
kern/debug/kdebug.c:328:2: error: ‘for’ loop initial declarations are only allowed in C99 mode所以没有用for
void
print_stackframe(void) {
uint32_t ebp = read_ebp();
uint32_t eip = read_eip();
int i = 0, j = 0;
while(i < STACKFRAME_DEPTH && ebp) // ebp 为0时表明程序返回到了最开始初始化的函数 {
cprintf("ebp:0x%08x eip:0x%08x args:", ebp, eip);
uint32_t* arguments = (uint32_t)ebp + 2; // 获得参数地址
j = 0;
while(j < 4) {
cprintf("0x%08x ", arguments[j]);
j++;
}
cprintf("\n");
print_debuginfo(eip - 1);
eip = *(uint32_t*)(ebp + 4);
ebp = *(uint32_t*)ebp; // 更新 eip, ebp
i++;
}
}输出为
ebp:0x00007b08 eip:0x001009a6 args:0x0c9c0000 0x00940010 0x00000001 0x7b380000
kern/debug/kdebug.c:306: print_stackframe+21
ebp:0x00007b18 eip:0x00100c9c args:0x00920000 0x00000010 0x00000000 0x00000000
kern/debug/kmonitor.c:125: mon_backtrace+10
ebp:0x00007b38 eip:0x00100092 args:0x00bb0000 0x00000010 0x7b600000 0x00000000
kern/init/init.c:48: grade_backtrace2+33
ebp:0x00007b58 eip:0x001000bb args:0x00d90000 0x00000010 0x00000000 0x7b84ffff
kern/init/init.c:53: grade_backtrace1+38
ebp:0x00007b78 eip:0x001000d9 args:0x00fe0000 0x00000010 0x00000000 0x00000010
kern/init/init.c:58: grade_backtrace0+23
ebp:0x00007b98 eip:0x001000fe args:0x00550000 0x32fc0010 0x32e00010 0x130a0010
kern/init/init.c:63: grade_backtrace+34
ebp:0x00007bc8 eip:0x00100055 args:0x7d680000 0x00000000 0x00000000 0x00000000
kern/init/init.c:28: kern_init+84
ebp:0x00007bf8 eip:0x00007d68 args:0x7c4f0000 0xfcfa0000 0xd88ec031 0xd08ec08e
<unknow>: -- 0x00007d67 --其中最后一行对应 bootmain.c 中的 bootmain 函数，bootmain中ebp为0x7bf8。返回地址eip为0x0000d64，之后四个是参数args:0x7c4f0000 0xfcfa0000 0xd88ec031 0xd08ec08e
完善中断初始化和处理
1. 中断描述符表（也可简称为保护模式下的中断向量表）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？
一个表项占8个字节，其中第0-15，48-63位代表中断处理代码的入口
2. 完善kern/trap/trap.c中对中断向量表进行初始化的函数idt_init。
void
idt_init(void) {
extern uintptr_t __vectors[];
int i = 0;
while(i < 256) {
SETGATE(idt[i], 0 ,GD_KTEXT ,__vectors[i], DPL_KERNEL);
i++;
}
SETGATE(idt[T_SYSCALL], 1, GD_KTEXT, __vectors[T_SYSCALL], DPL_USER);
lidt(&idt_pd);
}3. 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函数中处理时钟中断的部分，使操作系统每遇到100次时钟中断后，调用print_ticks子程序，向屏幕上打印一行文字”100 ticks”
case IRQ_OFFSET + IRQ_TIMER:
ticks = (ticks + 1) % TICK_NUM;
if(ticks == 0)
print_ticks();
break;