i386/junos/standford/2004/src/lab2/boot/main.c

   1
   2 #include <inc/x86.h>
   3 #include <inc/elf.h>
   4
   5 /**********************************************************************
   6  * This a dirt simple boot loader, whose sole job is to boot
   7  * an elf kernel image from the first IDE hard disk.
   8  *
   9  * DISK LAYOUT
  10  *  * This program(boot.S and main.c) is the bootloader.  It should
  11  *    be stored in the first sector of the disk.
  12  *
  13  *  * The 2nd sector onward holds the kernel image.
  14  *
  15  *  * The kernel image must be in ELF format.
  16  *
  17  * BOOT UP STEPS
  18  *  * when the CPU boots it loads the BIOS into memory and executes it
  19  *
  20  *  * the BIOS intializes devices, sets of the interrupt routines, and
  21  *    reads the first sector of the boot device(e.g., hard-drive)
  22  *    into memory and jumps to it.
  23  *
  24  *  * Assuming this boot loader is stored in the first sector of the
  25  *    hard-drive, this code takes over...
  26  *
  27  *  * control starts in bootloader.S -- which sets up protected mode,
  28  *    and a stack so C code then run, then calls cmain()
  29  *
  30  *  * cmain() in this file takes over, reads in the kernel and jumps to it.
  31  **********************************************************************/
  32
  33 #define  SECTOR_SIZE    512
  34
  35 static u_char *sect = (u_char*)0x10000; // scratch space
  36
  37 void readsect(u_char*, u_int, u_int);
  38 void readseg(u_int, u_int, u_int);
  39
  40 void
  41 cmain(void)
  42 {
  43         u_int entry, i;
  44         struct Elf *elf;
  45         struct Proghdr *ph;
  46
  47         // read 1st page off disk
  48         readsect(sect, 8, 1);
  49
  50         if(*(u_int*)sect != 0x464C457F) // \x7F ELF in little endian
  51                 goto bad;
  52
  53         // look at ELF header - ignores ph flags
  54         elf = (struct Elf*)sect;
  55         entry = elf->e_entry;
  56         ph = (struct Proghdr*)(sect+elf->e_phoff);
  57         for(i=0; i<elf->e_phnum; i++, ph++)
  58                 readseg(ph->p_va, ph->p_memsz, ph->p_offset);
  59
  60         entry &= 0xFFFFFF;
  61         ((void(*)(void))entry)();
  62         /* DOES NOT RETURN */
  63
  64 bad:
  65         outw(0x8A00, 0x8A00);
  66         outw(0x8A00, 0x8E00);
  67         for(;;);
  68
  69 }
  70
  71 // read count bytes at offset from kernel into addr dst
  72 // might copy more than asked
  73 void
  74 readseg(u_int va, u_int count, u_int offset)
  75 {
  76         u_int i;
  77
  78         va &= 0xFFFFFF;
  79
  80         // round down to sector boundary; offset will round later
  81         i = va&511;
  82         count += i;
  83         va -= i;
  84
  85         // translate from bytes to sectors
  86         offset /= 512;
  87         count = (count+511)/512;
  88
  89         // kernel starts at sector 1
  90         offset++;
  91
  92         // if this is too slow, we could read lots of sectors at a time.
  93         // we'd write more to memory than asked, but it doesn't matter --
  94         // we load in increasing order.
  95         for(i=0; i<count; i++){
  96                 readsect((u_char*)va, 1, offset+i);
  97                 va += 512;
  98         }
  99 }
 100
 101 void
 102 notbusy(void)
 103 {
 104         while(inb(0x1F7) & 0x80);       // wait for disk not busy
 105 }
 106
 107 void
 108 readsect(u_char *dst, u_int count, u_int offset)
 109 {
 110         notbusy();
 111
 112         outb(0x1F2, count);
 113         outb(0x1F3, offset);
 114         outb(0x1F4, offset>>8);
 115         outb(0x1F5, offset>>16);
 116         outb(0x1F6, (offset>>24)|0xE0);
 117         outb(0x1F7, 0x20);      // cmd 0x20 - read sectors
 118
 119         notbusy();
 120
 121         insl(0x1F0, dst, count*512/4);
 122 }
 123