#include "system.h"

void *memcpy(void *dest, const void *src, size_t count)
{
    const char *sp = (const char *)src;
    char *dp = (char *)dest;
    for(; count != 0; count--) *dp++ = *sp++;
    return dest;
}

int *memset(void *dest, char val, size_t count)
{
    char *temp = (char *)dest;
    for( ; count != 0; count--) *temp++ = val;
    return dest;
}

unsigned short *memsetw(unsigned short *dest, unsigned short val, size_t count)
{
    unsigned short *temp = (unsigned short *)dest;
    for( ; count != 0; count--) *temp++ = val;
    return dest;
}

size_t strlen(const char *str)
{
    size_t retval;
    for(retval = 0; *str != '\0'; str++) retval++;
    return retval;
}

unsigned char inportb (unsigned short _port)
{
    unsigned char rv;
    __asm__ __volatile__ ("inb %1, %0" : "=a" (rv) : "dN" (_port));
    return rv;
}

void outportb (unsigned short _port, unsigned char _data)
{
    __asm__ __volatile__ ("outb %1, %0" : : "dN" (_port), "a" (_data));
}

int main()
{
    int i;

    gdt_install();
    idt_install();
    isrs_install();
    irq_install();
    init_video();
    timer_install();
    keyboard_install();

    __asm__ __volatile__ ("sti");

    puts("Willkommen im MF OS 1.0\n");

//    i = 10 / 0;
//    putch(i);

    for (;;);
}

und das ist die headerdatei

#ifndef __SYSTEM_H
#define __SYSTEM_H

typedef int size_t;

/* This defines what the stack looks like after an ISR was running */
struct regs
{
    unsigned int gs, fs, es, ds;
    unsigned int edi, esi, ebp, esp, ebx, edx, ecx, eax;
    unsigned int int_no, err_code;
    unsigned int eip, cs, eflags, useresp, ss;    
};

/* MAIN.C */
extern void *memcpy(void *dest, const void *src, size_t count);
extern void *memset(void *dest, char val, size_t count);
extern unsigned short *memsetw(unsigned short *dest, unsigned short val, size_t count);
extern size_t strlen(const char *str);
extern unsigned char inportb (unsigned short _port);
extern void outportb (unsigned short _port, unsigned char _data);

/* CONSOLE.C */
extern void init_video(void);
extern void puts(unsigned char *text);
extern void putch(unsigned char c);
extern void cls();

/* GDT.C */
extern void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran);
extern void gdt_install();

/* IDT.C */
extern void idt_set_gate(unsigned char num, unsigned long base, unsigned short sel, unsigned char flags);
extern void idt_install();

/* ISRS.C */
extern void isrs_install();

/* IRQ.C */
extern void irq_install_handler(int irq, void (*handler)(struct regs *r));
extern void irq_uninstall_handler(int irq);
extern void irq_install();

/* TIMER.C */
extern void timer_wait(int ticks);
extern void timer_install();

/* KEYBOARD.C */
extern void keyboard_install();

#endif

Ich benütze den DevCpp Compiler und er kann dass nicht compilieren

was meckert er denn? multiple definitions o.ä.?

Ich benütze den DevCpp Compiler und er kann dass nicht compilieren

das ist keine fehlerbeschreibung.