Making a small/simple OS in C - some errors

[Arightwizard]

Sup. I've been working on an OS in C, (and still the mission idea (sorry, goatboy, btw, didnt notice you said to email it and yet i pm'ed.)) as a part time/side thing. Of course I can't just start from complete scratch, because of my inexperience in C, so I use snippets of other people's kernel code mixed with my own (I don't intend to sell it, just for my personal use, so I guess I can do that).

The process (in Ubuntu) I go through is as follows:

1. Write kernel.c, loader.s
2. Generate a pad file
3. Download other people's "stage1", "stage2", and "linker.ld" files (linker.ld to link everything)
4. Compile [gcc]
5. Link [ld]
6. Test.

However, on the linking process I get the following errors regarding kernel.o [compiled kernel.c]
Command:

Code: Select all

ld -T linker.ld -o kernel.bin loader.o kernel.o



Error:

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kernel.o: In function `kmain':
kernel.c:(.text+0x47): undefined reference to `gets'

My code for kernel.c (Compiled into kernel.o):

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#define WHITE_TXT 0x07 // white on black text
#include <stdio.h>
unsigned int k_printf(char *message, unsigned int line);
void k_clear_screen();
void update_cursor(int row, int col);
void kmain( void* mbd, unsigned int magic )
{
   if ( magic != 0x2BADB002 )
   {

   }

   char * boot_loader_name =(char*) ((long*)mbd)[16];

   /* Print a letter to screen to see everything is working: */
   unsigned char *videoram = (unsigned char *) 0xb8000;
   videoram[1] = 0x07; /* forground, background color. */

// TERMINAL TIMMMEEEEE!!!!!
char input[150];
k_clear_screen();
k_printf("Welcome to my simple OS! \nType some text and I'll echo it back for you: ", 4);
gets(input);
k_printf("You typed: %s", 6);

}

void k_clear_screen() // clear the entire text screen

{

   char *vidmem = (char *) 0xb8000;

   unsigned int i=0;

   while(i < (80*25*2))

   {

      vidmem[i]=' ';

      i++;

      vidmem[i]=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[i]=*message;
*message++;
i++;
vidmem[i]=WHITE_TXT;
i++;
};
};
return(1);
};

Code part with gets():

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// TERMINAL TIMMMEEEEE!!!!!
char input[150];
k_clear_screen();
k_printf("Welcome to my simple OS! \nType some text and I'll echo it back for you: ", 4);
gets(input);
k_printf("You typed: %s", 6);

PS: Yes, I know it's unsafe to use gets() instead of fgets(), but I haven't gotten far enough into development where it matters yet.

Anyone know how to fix this/what the problem even is? thanks!

[fashizzlepop]

Is that even legal in this simple of an OS? I would try another function instead. Or just delete that piece and see if it will compile and print out that other stuff first.

OS developing is incredibly intense. If you say you are inexperienced in C, learn C first extremely well. You will FAIL miserably if you can't even use pointers and other techniques popular in C.

So, go learn C.

[Arightwizard]

Is that even legal in this simple of an OS? I would try another function instead. Or just delete that piece and see if it will compile and print out that other stuff first.

OS developing is incredibly intense. If you say you are inexperienced in C, learn C first extremely well. You will FAIL miserably if you can't even use pointers and other techniques popular in C.

So, go learn C.

The other parts worked, I kinda did this step-by-step (Write a little, compile, test, repeat) to make sure I knew exactly where I was messing up if anything did mess up.

And I'm not really planning to succeed (even if I do, I DEFINITELY don't plan for a GUI to be involved... But, I think this would be a good learning experience for me, I've always learned in a way that, I have to completely drown myself in the language to understand. So an OS, with no outside support for functions, is a great way for me to learn some C.

I've tried other functions, too, like getchar, but those fail as well. I guess I'll try other functions like scanf or whatever else.
Thanks, if you didn't mention that it probably isn't possible in a simple environment, I probably wouldn't've thought about it, and kept trying to use gets().

[fashizzlepop]

Having code that takes input from the keyboard means your kernel has to have keyboard support, which most likely it doesn't have.

[Arightwizard]

Having code that takes input from the keyboard means your kernel has to have keyboard support, which most likely it doesn't have.

....I'm completely....completely retarded. No lie.
I didn't think about it, but I guessed C code, when compiled, would implement required components (like keyboard support ones) for the functions used and included.

lol see? This is a good learning experience so far, for C and for OS designing that I can use for future reference if I ever become serious about it.

[fashizzlepop]

I think it will end up slowing you down since you will be way lost on most of it. IMHO

[Arightwizard]

I think it will end up slowing you down since you will be way lost on most of it. IMHO

actually i'm working on it right now, it seems simple - just need to handle the qwerty key mapping, stop any interrupts, and whatever else. Thanks again, though.

Once again though, I don't plan for this succeed past a certain point - I know I'ma fuck it up at one point, a 13 year old kid like me can't possibly code a full blown, functional OS. [Oh, yeah, btw, I'm a little kid. Probably not too shocking.] But, what's the point of not starting to try at a certain point? - I mean, in case I plan to design a serious one later, I may as well start now just in case.

[neuromanta]

I think you have massive misconceptions about the definition of an OS as well. The OS kernel implements the low level hardware handling (luckily it can rely on the services of the BIOS), and the higher layers of the OS gives some basic applications with which the user can work. For example in the case of GNU/Linux, the Linux is the kernel and the basic applications (like cat, echo, ls, etc.) comes from the GNU system. I don't want to pour cold water on you (cuz I like your enthusiasm), but what you did is not even close to being an OS.

[Arightwizard]

I think you have massive misconceptions about the definition of an OS as well. The OS kernel implements the low level hardware handling (luckily it can rely on the services of the BIOS), and the higher layers of the OS gives some basic applications with which the user can work. For example in the case of GNU/Linux, the Linux is the kernel and the basic applications (like cat, echo, ls, etc.) comes from the GNU system. I don't want to pour cold water on you (cuz I like your enthusiasm), but what you did is not even close to being an OS.

I just figured (for now) I'd save time by trying to mix the two. I'd still consider it an OS, though, because an OS is just "operating system" - so, software the computer with which the computer uses to perform, just, whatever. So even if I mix the kernel with the terminal (if I can call it that at this stage lol), it'd still be, by my definition, an OS.

But, I said "(for now)" in this post, meaning that later on, I'll try to separate them so it actually functions like a regular OS...IF I make it that far.

[fashizzlepop]

I like the enthusiasm as well. You also seem pretty knowledgeable for a beginner.

I think it's appropriate to call it an OS.