OSDev.org

hi!!!

i am kinda amteur os dev. i jus started my codin some 1 week before. i have a decent knowledge in C and concepts of OS. asm is not my strong point.

i wrote this small hello-world kernel in C, making the kernel to boot with grub . then i tried my hand into writing clrscr() and printf functions. but unfortunately, my system freezes whenever it sees a function in my kernel. i am a bit stuck here. can anybody helpme out of this.

thnx in advance,
Charisma

what exactly works/doesn't work ?

if i decalre vram inside the kernel main funtion and then try to write it into vram it works. when i write the same procedure in some other funtion and then call it from the kernel main funtion, its not working.

kinda weird ... perhaps something with your stack size or with your arguments ... could you post the working "main" and the buggy "main+proc" function together with a short description of the execution environment (i.e. what segments are used, with their type, base and limit, at which address your code is loaded, etc.)

my program kernel.c with the asm calling program start.asm i am stating here...
the virtual address at which the kernel is loaded is 0xE0000000

-------------------
start.asm
------
;the initializations

   global KernelEntry
   extern tinymain
   extern _kernel_load_addr ;this is 0x00101000

   bits 32
   segment .text

;Multiboot header constants

F_PAGE_ALIGN equ 1<<0
F_MEM_FIELDS equ 1<<1

MAGIC       equ 0x1BADB002
FLAGS       equ F_PAGE_ALIGN | F_MEM_FIELDS
CHECKSUM   equ -(MAGIC + FLAGS)


KernelEntry:
   mov esp, _kernel_load_addr
   push ebx
   call init
   
   align 4
   dd MAGIC      ; Magic
   dd FLAGS      ; Flags
   dd CHECKSUM      ; Checksum



------------------------
kernel.c
----------------------------



#define WHITE_TXT 0x07


unsigned int k_printf(char *, unsigned int);

void init()
{
   char *vidmem = (char *) 0xb8000;
   unsigned int i=0;
   while(i < (80*25*2))
   {
      vidmem=' ';
      i++;
      vidmem=WHITE_TXT;
      i++;
   };//this works
   k_printf("Test",0); //this doesn't work
   while(1);
}


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);
}

hmm .. your stack initialisation routine seems weird to my sense . how do you ensure that it will have physical memory under 0x101000 ?
If there isn't, the CPU will raise a page fault when you have a stack overflow, but you have no PF handler ... and if you had one, you would have no stack to call it ... i guess this is where your triple fault comes from

try to have a that will guarantee you a clean stack

Try loading your kernel at 0x1000 ( if you can, I don't know if grub allows you ) untill you run out of room, so you can learn for awhile and then worrie about the loading thing