Hello OS!

[2100-OS]

OK, starting to create an OS using ASM (ofcourse), C and C++. The first thing I want to do is to display the famous text "Hello world!" on to the screen.

I am using DJGPP to compile a simple C file to an object file and NASM to compile the assembler part. When I compile the assembler part and the C part it all goes well.

When I link it goes wrong, it says:

ks.o(.text+0x1): undefined reference to `_k_main'
kernel.o(.eh_frame+0x11):kernel.c: undefined reference to `___gxx_personality_v0

Thus checking the assembler file (ks.o is from this one) but i did have an extern to this one, and in the C file it's named k_main (without the leading _ ). In the kernel.c file I can't find any ___gxx..._v0, so I think I'm doing something wrong with the compiler options.

The way I'm doing it now:

nasmw -f aout kernel_start.asm -o ks.o
gpp -c kernel.c -o kernel.o
ld -T link.ld -o kernel.bin ks.o kernel.o

here it goes wrong.

Please inform me if I'm doing something wrong, and what I'm doing wrong.

The files I use:

kernel_start.asm:

%include "grub.inc" ; needed for the multiboot header

[BITS 32]

[global start]
[extern _k_main] ; this is in the c file

start:
call _k_main

cli ; stop interrupts
hlt ; halt the CPU

EXTERN code, bss, end

ALIGN 4
mboot:
   dd MULTIBOOT_HEADER_MAGIC
   dd MULTIBOOT_HEADER_FLAGS
   dd MULTIBOOT_CHECKSUM
   dd mboot
   dd code
   dd bss
   dd end
   dd start


grub.inc

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)


kernel.c:

#define WHITE_TXT 0x07 // white on black text

void k_clear_screen();
unsigned int k_printf(char *message, unsigned int line);

void k_main( void ) // like main in a normal C program
{
   k_clear_screen();
   k_printf("Hi!\nHow's this for a starter OS?", 0);
}

void k_clear_screen() // clear the entire text screen
{
   char *vidmem = (char *) 0xb8000;
   unsigned int i=0;
   while(i < (80*25*2))
   {
      vidmem=' ';
      i++;
      vidmem=WHITE_TXT;
      i++;
   }
}

unsigned int k_printf(char *message, unsigned int line) // the message and then the line #
{
   char *vidmem = (char *) 0xb8000;
   unsigned int i=0;

   i=(line*80*2);

   while(*message!=0)
   {
      if(*message=='\n') // check for a new line
      {
         line++;
         i=(line*80*2);
         *message++;
      } else {
         vidmem=*message;
         *message++;
         i++;
         vidmem=WHITE_TXT;
         i++;
      }
   }
   return 1;
}


link.ld

OUTPUT_FORMAT("binary")
ENTRY(start)
SECTIONS
{
.text 0x100000 : {
code = .; _code = .; __code = .;
*(.text)
. = ALIGN(4096);
}
.data : {
data = .; _data = .; __data = .;
*(.data)
. = ALIGN(4096);
}
.bss :
{
bss = .; _bss = .; __bss = .;
*(.bss)
. = ALIGN(4096);
}
end = .; _end = .; __end = .;
}

[whyme_t]

undefined reference to `___gxx_personality_v0

gpp -c kernel.c -o kernel.o

What is gpp? Is it the same as gxx?, which is the C++ compiler. I think you should try

Code: Select all

gcc -c kernel.c -o kernel.o

I believe ___gxx_personality_v0 is a builtin function that is something to do with C++ exception handling.

EDIT:- I just compiled your code, and I get the same error when using gpp, but it works fine with gcc.

[2100-OS]

That just solved the problem, Indeed I was mistaking gpp with gcc, which is only the C++ compiler, now I understand that second error too.

thanks for clearing this up