OSDev.org

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OUTPUT_FORMAT("elf32-i386")
ENTRY(loader)
phys = 0x00100000;

SECTIONS
{
    .text phys : AT(phys) {
        code = .;
        *(.text)
        *(.rodata)
        . = ALIGN(4096);
    }

    .data : AT(phys + (data - code))
    {
        data = .;
        *(.data)
        . = ALIGN(4096);
    }

    .bss : AT(phys + (bss - code))
    {
        bss = .;
        *(.bss)
        . = ALIGN(4096);
    }

    end = .;
}

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[BITS 32]

global loader

mboot:

    ; Multiboot macros to make a few lines later more readable
    MULTIBOOT_PAGE_ALIGN    equ 1<<0
    MULTIBOOT_MEMORY_INFO   equ 1<<1
    MULTIBOOT_AOUT_KLUDGE   equ 1<<16
    MULTIBOOT_HEADER_MAGIC  equ 0x1BADB002
    MULTIBOOT_HEADER_FLAGS  equ MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE
    MULTIBOOT_CHECKSUM      equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)

    ; This part MUST be 4byte aligned
    align 4

    ; Declared in linker.ld
    extern code, bss, end

    ; This is the GRUB Multiboot header. A boot signature
    dd MULTIBOOT_HEADER_MAGIC
    dd MULTIBOOT_HEADER_FLAGS
    dd MULTIBOOT_CHECKSUM

    dd mboot
    dd code
    dd bss
    dd end
    dd loader

loader:
    ; This points the stack to our new stack area
    mov esp, _system_stack

    push eax ; Multiboot magic number
    push ebx ; Multiboot info structure

    extern k_main
    call k_main

    hlt

; Remember that a stack actually grows
; downwards, so we declare the size of the data before declaring
; the identifier '_system_stack'
SECTION .bss

    resb 8192               ; This reserves 8KBytes of memory here

_system_stack:

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#ifndef _KERNEL_TERMINAL_H
#define _KERNEL_TERMINAL_H

extern const uint64_t VIDEO_RAM_ADDRESS;
extern const uint16_t TERMINAL_COLUMNS;
extern const uint16_t TERMINAL_LINES;

typedef struct terminal_cursor
{
    uint16_t x;
    uint16_t y;
} terminal_cursor_t;

extern void itoa (char *destination, const char base, const int32_t integer);
extern void putchar (const char ch);
extern void print_formatted (const char *format, ...);
extern void clear_screen ();
extern void init_terminal ();

#endif /* _KERNEL_TERMINAL_H */

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#include <kernel/types.h>
#include <kernel/terminal.h>

const uint64_t VIDEO_RAM_ADDRESS = 0xB8000;
const uint16_t TERMINAL_COLUMNS = 80;
const uint16_t TERMINAL_LINES = 25;

const uint8_t ATTRIBUTE = 0x07;

volatile uint8_t *video_ram;
static terminal_cursor_t cursor;

void
itoa (char *destination, const char base, const int32_t integer)
{
    char *buffer = destination;
    char *temp1, *temp2;
    uint32_t unsigned_integer = integer;
    uint16_t divisor = 10;

    /* If %d is specified and integer is minus, put `-' in the head. */
    if (base == 'd' && integer < 0) {
        *buffer++ = '-';
        destination++;
        unsigned_integer = -integer;
    } else if (base == 'x') {
        divisor = 16;
    }

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

    /* Terminate BUF. */
    *buffer = 0;

    /* Reverse BUF. */
    temp1 = buffer;
    temp2 = buffer - 1;
    while (temp1 < temp2) {
        uint8_t temp = *temp1;
        *temp1 = *temp2;
        *temp2 = temp;
        temp1++;
        temp2--;
    }
}

void
put_character (const char ch)
{
    if (ch == '\n' || ch == '\r')
    {
        _NEWLINE:
            cursor.x = 0;
            cursor.y++;
            if (cursor.y >= TERMINAL_LINES)
                cursor.y = 0;
            return;
    }

    *(video_ram + (cursor.x + cursor.y * TERMINAL_COLUMNS) * 2) = ch & 0xFF;
    *(video_ram + (cursor.x + cursor.y * TERMINAL_COLUMNS) * 2 + 1) = ATTRIBUTE;

    cursor.x++;
    if (cursor.x >= TERMINAL_COLUMNS)
        goto _NEWLINE;
}

/* not important things... */

void
print_formatted (const char *format, ...)
{
    char **arguments = (char **) &format;
    char ch;
    char buffer[20];

    arguments++;

    while ((ch = *format++) != 0) {
        if (ch != '%') {
            put_character(ch);
        } else {
            char *next_ch;
            ch = *format++;
            switch (ch)
            {
                case 'd':
                case 'u':
                case 'x':
                    itoa(buffer, ch, *((int32_t *)arguments++));
                    next_ch = buffer;
                    goto _STRING;
                    break;
                case 's':
                    next_ch = *arguments++;
                    if (!next_ch)
                        next_ch = "(null)";
                    _STRING:
                        while (*next_ch)
                            put_character(*next_ch++);
                    break;
                default:
                    put_character(*((char *)arguments++));
                    break;
            }
        }
    }
}

void
init_terminal ()
{
    video_ram = (volatile uint8_t *)VIDEO_RAM_ADDRESS;
    clear_screen();
    print_formatted("Hello World!\n");
    print_formatted("2 + 2 = %d!\n", 2 + 2);
    print_formatted("...which is in hexadecimal... %x!\n", 2 + 2);
}

Code: Select all

#include <kernel/types.h>
#include <kernel/terminal.h>

void
k_main (uint64_t magic, uint64_t *multiboot_informations)
{
    init_terminal();
    put_character('a');              // Just fine

    /* HERE'S THE PROBLEM */
        print_formatted("Anything");
    /* / HERE'S THE PROBLEM */

    while (0==0)
        /* nothing */;
}

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mikoskay@mikoskay:~/Projects/os$ mbchk bin/kernel.bin
bin/kernel.bin: The Multiboot header is found at the offset 4736.
bin/kernel.bin: Page alignment is turned on.
bin/kernel.bin: Memory information is turned on.
bin/kernel.bin: Address fields is turned on.
bin/kernel.bin: All checks passed.
mikoskay@mikoskay:~/Projects/os$ objdump -h bin/kernel.bin                                                                                         

bin/kernel.bin:     file format elf32-i386

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00001000  00100000  00100000  00001000  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .rodata.str1.1 00000022  00101000  00101000  00002000  2**0
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  2 .rodata.str1.4 00000024  00101024  00101024  00002024  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  3 .data         00000fb8  00101048  00101048  00002048  2**3
                  CONTENTS, ALLOC, LOAD, DATA
  4 .bss          00003004  00102000  00102000  00003000  2**3
                  ALLOC
  5 .comment      0000001c  00000000  00000000  00003000  2**0
                  CONTENTS, READONLY

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mikoskay@mikoskay:~/Projects/os$ mbchk bin/kernel.bin
bin/kernel.bin: No Multiboot header.
mikoskay@mikoskay:~/Projects/os$ objdump -h bin/kernel.bin 

bin/kernel.bin:     file format elf32-i386

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .rodata.str1.1 0000002b  00000000  00000000  00001000  2**0
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  1 .rodata.str1.4 00000024  0000002c  0000002c  0000102c  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  2 .text         00001000  00100000  00100000  00002000  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  3 .bss          00003004  00101000  00101000  00003000  2**3
                  ALLOC
  4 .comment      0000001c  00000000  00000000  00003000  2**0
                  CONTENTS, READONLY

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.rodata
.rodata.hello 
.rodata.randomstring 
.rodata.really.bizarre.section.name

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multiboot_section_start = 0x00100000;
multiboot_section_end = 0x00102000;

(...)

    .text : {
        . = multiboot_section_start;
        mboot = .;
        . = multiboot_section_end;
        code = .;
        *(.text)
        *(.rodata)
        . = ALIGN(4096);
    }

(...)