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# loader.s

.global _loader            # making entry point visible to linker

# setting up the Multiboot header - see GRUB docs for details
.set ALIGN,     1<<0                     # align loaded modules on page boundaries
.set MEMINFO,  1<<1                      # provide memory map
.set FLAGS,     ALIGN | MEMINFO  # this is the Multiboot 'flag' field
.set MAGIC,     0x1BADB002         # 'magic number' lets bootloader find the header
.set CHECKSUM, -(MAGIC + FLAGS) # checksum required

.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM

# reserve initial kernel stack space
.set STACKSIZE, 0x4000            # that's 16k.
.comm stack, STACKSIZE, 32        # reserve 16k stack on a quadword boundary

_loader:           mov   $(stack + STACKSIZE), %esp # set up the stack
                           push  %eax                                      # Multiboot magic number
                           push  %ebx                                      # Multiboot data structure

                           call  _main                  # call kernel proper
                           hlt                                  # halt machine should kernel return

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TARGET (elf32-i386)
ENTRY (_loader)

SECTIONS
{
    . = 0x00100000;

    .text :
    {
        *(.text)
        *(.rodata)
    }

    .data ALIGN (0x1000) :
    {
        *(.data)
    }

    .bss :
    {
        _sbss = .;
        *(COMMON)
        *(.bss)
        _ebss = .;
    }
}

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#include "video.h"

video *Video;

int _main(void* mbd, unsigned int magic)
{
        Video = video_create();
        video_write(Video, "Hello there folks.");

        return 0;
}

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#ifndef VIDEO_H
#define VIDEO_H

typedef struct {
        unsigned short *mem;
        unsigned int off, pos;
} video;

int video_put(video *Video, char ch);
int video_write(video *Video, char *buf);
video *video_create();

#endif

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#include "video.h"

video *video_create()
{
        video *new;
        new->mem = (unsigned short*) 0xb8000;
        new->off = 0;
        new->pos = 0;
        return new;
}

int video_write(video *Video, char *buf)
{
        int i;
        for (i=0;i<sizeof(buf);i++) {
                video_put(Video, buf[i]);
        }

        return i;
}

int video_put(video *Video, char ch)
{
        if (Video->pos <= 80) {
                Video->pos = 0;
                Video->off += 80;
        }

        Video->mem[Video->off + Video->pos] = (unsigned char) ch | 0x0700;
        Video->pos++;

        return 1;
}

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as   -o loader.o loader.s
gcc  -c kernel.c -o kernel.o -Wall -Werror -nostdlib -nostartfiles -nodefaultlibs
gcc  -c video.c -o video.o -Wall -Werror -nostdlib -nostartfiles -nodefaultlibs
ld -T link.ld loader.o kernel.o video.o -o popcorn

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        video *new;
        new->mem = (unsigned short*) 0xb8000;
        new->off = 0;
        new->pos = 0;
        return new;