Lab1-Part C -1/2: The Kernel (Taste of MM/Output)

[Preface] A Hope That My Crude Remarks May Draw Forth By Abler People
[前言]拋磚引玉


Exercise7:

• Something needed to know.
• Examine before and after Paging Enable.
1. brack at  movl %eas,%cr0 to check 0x00100000/0xf0100000
• x/20h 0x100000
  0x100000:       0xb002  0x1bad  0x0000  0x0000  0x4ffe  0xe452  0xc766  0x72050
  x100010:       0x0004  0x3400  0xb812  0x0000  0x0011  0x220f  0x0fd8  0xc020
  0x100020:       0x010d  0x0100  0x0f80  0xc022
• x/20h 0xf0100000
  0xf0100000:     0xffff  0xffff  0xffff  0xffff  0xffff  0xffff  0xffff  0xffff
  0xf0100010:     0xffff  0xffff  0xffff  0xffff  0xffff  0xffff  0xffff  0xffff
  0xf0100020:     0xffff  0xffff  0xffff  0xffff
2. si then check again.
   
   • x/20h 0x100000
     0x100000:       0xb002  0x1bad  0x0000  0x0000  0x4ffe  0xe452  0xc766  0x7205
     0x100010:       0x0004  0x3400  0xb812  0x0000  0x0011  0x220f  0x0fd8  0xc020
     0x100020:       0x010d  0x0100  0x0f80  0xc022
   • x/20h 0xf0100000
     0x100000:       0xb002  0x1bad  0x0000  0x0000  0x4ffe  0xe452  0xc766  0x7205
     0x100010:       0x0004  0x3400  0xb812  0x0000  0x0011  0x220f  0x0fd8  0xc020
     0x100020:       0x010d  0x0100  0x0f80  0xc022  
3. They are mapped.
• Geuss where would be happaned, if mapping weren't in place by commenting out movl %eas,%cr0.
• mov     $relocated, %eax
  jmp     *%eax #<---Here
• Why?
1. $relocate is addressed as 0xf0100025(by VMA:0xf0100000), but commenting out the line,enabling protected mode. It resulted in mapping failed.
• No protected mode no mapping from 0xf010000c to 0x10000c(phy address) at view of entry address.
2. By the way, above code could be executed because the bootloader directly move/copy/jmp in real address. (know details by the following discussion)
• Discussion:
• How did kernel execute its start address at 0x10000c?
1. BIOS read disk's #0 sector(boot sector) and load them into ram:0x7C00 to execute
2. bootload read disk's #1 sector and load them into ram:0x100000 to execute
• dd command put kernel into #1 sector.
3. bootloader jump to kernel's start entry address by ((void (*)(void)) (ELFHDR->e_entry))();
• After Lesson:
  • What did kernel.asm do from 0x100000 to 0x10000c
  • .globl entry
  • entry:
  •         movw    $0x1234,0x472                   # warm boot                                         f0100000:       02 b0 ad 1b 00 00       add    0x1bad(%eax),%dh
  • f0100006:       00 00                   add    %al,(%eax)
  • f0100008:       fe 4f 52                decb   0x52(%edi)                                           f010000b:       e4 66                   in     $0x66,%al
  • f010000c <entry>:

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Exercise8:

• Something needed to kow
• Trace code to understand the following code's relateionship.
• kern/printf.c
• kernel internal API function 
• lib/printfmt.c
• Utility to format output used by Kernel/User mode
• kern/console.c
• Driver
• Accomplish to print "%o" for octal.
• 209                         num = getuint(&ap, lflag);
• 210                         base = 8;
• 211                         goto number;
• Discussion:
1. Interface between console.c and printf.c
• Exported by inc/stdio.h
• cputchar by printf.c
• getchar;by readline.c
• iscons ;by readline.c
• Exported by inc/console.h
• cons_init; by init.c
• cons_getc;
• kbd_intr
• serial_intr
2.  Roll up One Empty line.
3. check arguments
• cprintf
• fmt=0xf0101a69 "x:%d,y:%d,z:%d\n"
• ap=0xf010ffe4 ("\001")
•  x/4w 0xf010ffe0
  0xf010ffe0:     0xf0101a69      0x00000001      0x00000003      0x00000004
• push order: arg4(0x0000004) arg3 arg2 arg1(0xf0101a69)
• pop order is the reverse.
• cons_putc/va_arg/vcprintf
1. order: vcprintf->va_arg->cons_putc
2. vcprintf:
   • fmt=0xf0101a69 "x:%d,y:%d,z:%d\n"
   • ap=0xf010ffe4 ("\001"
3. va_arg:
• the next stack address to print
4. cons_putc: 
• the int type variable to be printed on Screen.
4.  type translation and ASCII table
• Output "He110 World"
• 57616 (Decimal) = E110 (Hex)
• 0x00646c72 
• 0x72 :'r'
• 0x6c :'l'
• 0x64 :'d'
• 0x00 :'\0'
• Note: little endian printed.
5.  cprintf("x=%d y=%d",3)
•  y=%d in va_arg, it gets the next stack frame's value.
6. reverse order.
• After Lesson:
• Why is printfmt.c located in the separate lib directory?
• GitHub Link
• My Code

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