docs/kernel.c

/* kernel.c - the C part of the kernel */
/* Copyright (C) 1999  Free Software Foundation, Inc.
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

#include <multiboot.h>

/* Macros.  */

/* Check if the bit BIT in FLAGS is set.  */
#define CHECK_FLAG(flags,bit)	((flags) & (1 << (bit)))

/* Some screen stuff.  */
/* The number of columns.  */
#define COLUMNS			80
/* The number of lines.  */
#define LINES			24
/* The attribute of an character.  */
#define ATTRIBUTE		7
/* The video memory address.  */
#define VIDEO			0xB8000

/* Variables.  */
/* Save the X position.  */
static int xpos;
/* Save the Y position.  */
static int ypos;
/* Point to the video memory.  */
static volatile unsigned char *video;

/* Forward declarations.  */
void cmain (unsigned long magic, unsigned long addr);
static void cls (void);
static void itoa (char *buf, int base, int d);
static void putchar (int c);
void printf (const char *format, ...);

/* Check if MAGIC is valid and print the Multiboot information structure
   pointed by ADDR.  */
void
cmain (unsigned long magic, unsigned long addr)
{
  multiboot_info_t *mbi;
  
  /* Clear the screen.  */
  cls ();

  /* Am I booted by a Multiboot-compliant boot loader?  */
  if (magic != MULTIBOOT_BOOTLOADER_MAGIC)
    {
      printf ("Invalid magic number: 0x%x\n", magic);
      return;
    }

  /* Set MBI to the address of the Multiboot information structure.  */
  mbi = (multiboot_info_t *) addr;

  /* Print out the flags.  */
  printf ("flags = 0x%x\n", mbi->flags);

  /* Are mem_* valid?  */
  if (CHECK_FLAG (mbi->flags, 0))
    printf ("mem_lower = %dKB, mem_upper = %dKB\n",
	    mbi->mem_lower, mbi->mem_upper);

  /* Is boot_device valid?  */
  if (CHECK_FLAG (mbi->flags, 1))
    printf ("boot_device = 0x%x\n", mbi->boot_device);
  
  /* Is the command line passed?  */
  if (CHECK_FLAG (mbi->flags, 2))
    printf ("cmdline = %s\n", (char *) mbi->cmdline);

  /* Are mods_* valid?  */
  if (CHECK_FLAG (mbi->flags, 3))
    {
      module_t *mod;
      int i;
      
      printf ("mods_count = %d, mods_addr = 0x%x\n",
	      mbi->mods_count, mbi->mods_addr);
      for (i = 0, mod = (module_t *) mbi->mods_addr;
	   i < mbi->mods_count;
	   i++, mod += sizeof (module_t))
	printf (" mod_start = 0x%x, mod_end = 0x%x, string = %s\n",
		mod->mod_start, mod->mod_end, (char *) mod->string);
    }

  /* Bits 4 and 5 are mutually exclusive!  */
  if (CHECK_FLAG (mbi->flags, 4) && CHECK_FLAG (mbi->flags, 5))
    {
      printf ("Both bits 4 and 5 are set.\n");
      return;
    }

  /* Is the symbol table of a.out valid?  */
  if (CHECK_FLAG (mbi->flags, 4))
    {
      aout_symbol_table_t *aout_sym = &(mbi->u.aout_sym);
      
      printf ("aout_symbol_table: tabsize = 0x%0x, "
	      "strsize = 0x%x, addr = 0x%x\n",
	      aout_sym->tabsize, aout_sym->strsize, aout_sym->addr);
    }

  /* Is the section header table of ELF valid?  */
  if (CHECK_FLAG (mbi->flags, 5))
    {
      elf_section_header_table_t *elf_sec = &(mbi->u.elf_sec);

      printf ("elf_sec: num = %d, size = 0x%x,"
	      " addr = 0x%x, shndx = 0x%x\n",
	      elf_sec->num, elf_sec->size,
	      elf_sec->addr, elf_sec->shndx);
    }

  /* Are mmap_* valid?  */
  if (CHECK_FLAG (mbi->flags, 6))
    {
      memory_map_t *mmap;
      
      printf ("mmap_addr = 0x%x, mmap_length = 0x%x\n",
	      mbi->mmap_addr, mbi->mmap_length);
      for (mmap = (memory_map_t *) mbi->mmap_addr;
	   (unsigned long) mmap < mbi->mmap_addr + mbi->mmap_length;
	   mmap = (memory_map_t *) ((unsigned long) mmap
				    + mmap->size + sizeof (mmap->size)))
	printf (" size = 0x%x, base_addr = 0x%x%x,"
		" length = 0x%x%x, type = 0x%x\n",
		mmap->size, mmap->base_addr_high, mmap->base_addr_low,
		mmap->length_high, mmap->length_low, mmap->type);
    }
}    

/* Clear the screen and initialize VIDEO, XPOS and YPOS.  */
static void
cls (void)
{
  int i;

  video = (unsigned char *) VIDEO;
  
  for (i = 0; i < COLUMNS * LINES * 2; i++)
    *(video + i) = 0;

  xpos = 0;
  ypos = 0;
}

/* Convert the integer D to a string and save the string in BUF. If
   BASE is equal to 'd', interpret that D is decimal, and if BASE is
   equal to 'x', interpret that D is hexadecimal.  */
static void
itoa (char *buf, int base, int d)
{
  char *p = buf;
  char *p1, *p2;
  unsigned long ud = d;
  int divisor = 10;
  
  /* If %d is specified and D is minus, put `-' in the head.  */
  if (base == 'd' && d < 0)
    {
      *p++ = '-';
      buf++;
      ud = -d;
    }
  else if (base == 'x')
    divisor = 16;

  /* Divide UD by DIVISOR until UD == 0.  */
  do
    {
      int remainder = ud % divisor;
      
      *p++ = (remainder < 10) ? remainder + '0' : remainder + 'a' - 10;
    }
  while (ud /= divisor);

  /* Terminate BUF.  */
  *p = 0;
  
  /* Reverse BUF.  */
  p1 = buf;
  p2 = p - 1;
  while (p1 < p2)
    {
      char tmp = *p1;
      *p1 = *p2;
      *p2 = tmp;
      p1++;
      p2--;
    }
}

/* Put the character C on the screen.  */
static void
putchar (int c)
{
  if (c == '\n' || c == '\r')
    {
    newline:
      xpos = 0;
      ypos++;
      if (ypos >= LINES)
	ypos = 0;
      return;
    }

  *(video + (xpos + ypos * COLUMNS) * 2) = c & 0xFF;
  *(video + (xpos + ypos * COLUMNS) * 2 + 1) = ATTRIBUTE;

  xpos++;
  if (xpos >= COLUMNS)
    goto newline;
}

/* Format a string and print it on the screen, just like the libc
   function printf.  */
void
printf (const char *format, ...)
{
  char **arg = (char **) &format;
  int c;
  char buf[20];

  arg++;
  
  while ((c = *format++) != 0)
    {
      if (c != '%')
	putchar (c);
      else
	{
	  char *p;
	  
	  c = *format++;
	  switch (c)
	    {
	    case 'd':
	    case 'u':
	    case 'x':
	      itoa (buf, c, *((int *) arg++));
	      p = buf;
	      goto string;
	      break;

	    case 's':
	      p = *arg++;
	      if (! p)
		p = "(null)";

	    string:
	      while (*p)
		putchar (*p++);
	      break;

	    default:
	      putchar (*((int *) arg++));
	      break;
	    }
	}
    }
}