Hi everybody.
I have some questions about tutorials. More precisely those which are on bootloader running kernel written in c.
I followed step by step it but i don't have the same result : i boot but the c kernel doesn't seem to be read...
My computer runs with WinXP SP3. I use Notepad++ as text editor. I compile with the last version of nasm and DJGPP/GCC. I make my floppy images with makeboot and I run them with bochs. I tried with the partcopy, dd and vfd combo but without any success. I tried with Mingw/GCC... no more success. There is something i didn't see ?
I write below the code i used (which can be found on this website):
main.c
Code:
const char *tutorial3;
void main()
{
clrscr();
print(tutorial3);
for(;;);
}
const char *tutorial3 = "MuOS Tutorial 3";
video.c
Code:
void clrscr()
{
unsigned char *vidmem = (unsigned char *)0xB8000;
const long size = 80*25;
long loop;
// Clear visible video memory
for (loop=0; loop<size; loop++) {
*vidmem++ = 0;
*vidmem++ = 0xF;
}
// Set cursor position to 0,0
out(0x3D4, 14);
out(0x3D5, 0);
out(0x3D4, 15);
out(0x3D5, 0);
}
void print(const char *_message)
{
unsigned short offset;
unsigned long i;
unsigned char *vidmem = (unsigned char *)0xB8000;
// Read cursor position
out(0x3D4, 14);
offset = in(0x3D5) << 8;
out(0x3D4, 15);
offset |= in(0x3D5);
// Start at writing at cursor position
vidmem += offset*2;
// Continue until we reach null character
i = 0;
while (_message[i] != 0) {
*vidmem = _message[i++];
vidmem += 2;
}
// Set new cursor position
offset += i;
out(0x3D5, (unsigned char)(offset));
out(0x3D4, 14);
out(0x3D5, (unsigned char)(offset >> 8));
}
ports.c
Code:
unsigned char in(unsigned short _port)
{
// "=a" (result) means: put AL register in variable result when finished
// "d" (_port) means: load EDX with _port
unsigned char result;
__asm__ ("in %%dx, %%al" : "=a" (result) : "d" (_port));
return result;
}
void out(unsigned short _port, unsigned char _data)
{
// "a" (_data) means: load EAX with _data
// "d" (_port) means: load EDX with _port
__asm__ ("out %%al, %%dx" : :"a" (_data), "d" (_port));
}
loader.asm
Code:
[BITS 16] ; We need 16-bit intructions for Real mode
[ORG 0x7C00] ; The BIOS loads the boot sector into memory location 0x7C00
mov ah, 0Eh ; Display 'A'
mov al, 'A'
mov bh, 0Fh
mov bl, 0
int 10h
reset_drive:
mov ah, 0 ; RESET-command
int 13h ; Call interrupt 13h
or ah, ah ; Check for error code
jnz reset_drive ; Try again if ah != 0
mov ax, 0
mov es, ax
mov bx, 0x1000 ; Destination address = 0000:1000
mov ah, 02h ; READ SECTOR-command
mov al, 02h ; Number of sectors to read = 1
mov ch, 0 ; Cylinder = 0
mov cl, 02h ; Sector = 2
mov dh, 0 ; Head = 0
int 13h ; Call interrupt 13h
or ah, ah ; Check for error code
jnz reset_drive ; Try again if ah != 0
cli ; Disable interrupts, we want to be alone
xor ax, ax
mov ds, ax ; Set DS-register to 0 - used by lgdt
lgdt [gdt_desc] ; Load the GDT descriptor
mov eax, cr0 ; Copy the contents of CR0 into EAX
or eax, 1 ; Set bit 0
mov cr0, eax ; Copy the contents of EAX into CR0
jmp 08h:clear_pipe ; Jump to code segment, offset clear_pipe
[BITS 32] ; We now need 32-bit instructions
clear_pipe:
mov ax, 10h ; Save data segment identifyer
mov ds, ax ; Move a valid data segment into the data segment register
mov ss, ax ; Move a valid data segment into the stack segment register
mov esp, 090000h ; Move the stack pointer to 090000h
jmp 08h:01000h ; Jump to section 08h (code), offset 01000h
gdt: ; Address for the GDT
gdt_null: ; Null Segment
dd 0
dd 0
gdt_code: ; Code segment, read/execute, nonconforming
dw 0FFFFh
dw 0
db 0
db 10011010b
db 11001111b
db 0
gdt_data: ; Data segment, read/write, expand down
dw 0FFFFh
dw 0
db 0
db 10010010b
db 11001111b
db 0
gdt_end: ; Used to calculate the size of the GDT
gdt_desc: ; The GDT descriptor
dw gdt_end - gdt - 1 ; Limit (size)
dd gdt ; Address of the GDT
times 510-($-$$) db 0 ; Fill up the file with zeros
dw 0AA55h ; Boot sector identifyer
compile.bat
Code:
@echo on
nasm -f bin loader.asm -o loader.bin
gcc -ffreestanding -c main.c -o main.o
gcc -c video.c -o video.o
gcc -c ports.c -o ports.o
ld -e _main -Ttext 0x1000 -o kernel.o main.o video.o ports.o
ld -i -e _main -Ttext 0x1000 -o kernel.o main.o video.o ports.o
objcopy -R .note -R .comment -S -O binary kernel.o kernel.bin
makeboot floppy.img loader.bin kernel.bin
pause
bochs -f bochsrc.txt
So, does this code run for you? Could you display code dump for kernel.bin, loader.bin and floppy.img, and their size in bytes? Or tell me what software do you use and with which parameters?
Thanks you.
