Next: Other Multiboot kernels, Previous: boot.S, Up: Example OS code
And, in the file 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", (unsigned) 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", (unsigned) mbi->flags); /* Are mem_* valid? */ if (CHECK_FLAG (mbi->flags, 0)) printf ("mem_lower = %uKB, mem_upper = %uKB\n", (unsigned) mbi->mem_lower, (unsigned) mbi->mem_upper); /* Is boot_device valid? */ if (CHECK_FLAG (mbi->flags, 1)) printf ("boot_device = 0x%x\n", (unsigned) 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", (int) mbi->mods_count, (int) mbi->mods_addr); for (i = 0, mod = (module_t *) mbi->mods_addr; i < mbi->mods_count; i++, mod++) printf (" mod_start = 0x%x, mod_end = 0x%x, string = %s\n", (unsigned) mod->mod_start, (unsigned) 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", (unsigned) aout_sym->tabsize, (unsigned) aout_sym->strsize, (unsigned) 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 = %u, size = 0x%x," " addr = 0x%x, shndx = 0x%x\n", (unsigned) elf_sec->num, (unsigned) elf_sec->size, (unsigned) elf_sec->addr, (unsigned) 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", (unsigned) mbi->mmap_addr, (unsigned) 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", (unsigned) mmap->size, (unsigned) mmap->base_addr_high, (unsigned) mmap->base_addr_low, (unsigned) mmap->length_high, (unsigned) mmap->length_low, (unsigned) 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; } } } }