[ BIG CHANGE ] Properly Implemented IDT

- New include files: idt.h, pic.h, syscall.h and exceptions.h
- Proper exception handling (still could be improved
- PIC properly initiated and irqs all masked
- BREAKS Keyboard - The keyboard IRQ is not handled anymore
- convertColor() is kinda broken :/ (More in README.md)

include/syscall.h

@@ -0,0 +1,77 @@
+#ifndef SYSCALL_H
+#define SYSCALL_H
+
+#include "screen.h"
+
+// System call count
+#define MAX_SYSCALLS 2
+
+void sys_test0() {
+    fgColor = YELLOW;
+    print("Syscall 0 - Test\n");
+    fgColor = FG_COLOR;
+}
+
+void sys_test1() {
+    fgColor = CYAN;
+    print("Syscall 1 - Test\n");
+    fgColor = FG_COLOR;
+}
+
+// System call table
+void* syscalls[MAX_SYSCALLS] = {
+    sys_test0, 
+    sys_test1, 
+};
+
+// int 0x80 - Syscall interrupt, handled by this function
+// eax : Syscall number
+__attribute__ ((naked)) // No prologue or epilogue, just assembly
+void syscallHandler(void) {
+    // Interrupt - Stack should contain: ss, esp, eflags, cs, eip
+    // We should also push these regs: ax, gs, fs, es, ds, bp, di, si, dx, cx, bx
+    __asm__ volatile (
+            ".intel_syntax noprefix\n" // We use intel syntax
+            ".equ MAX_SYSCALLS, 2\n" // Define MAX_SYSCALLS again
+
+            // Check if syscall exists
+            "cmp eax, MAX_SYSCALLS - 1\n"
+            "ja invalidSyscall\n"
+
+            // Call the syscall
+            "push eax\n" // Push required values
+            "push gs\n"
+            "push fs\n"
+            "push es\n"
+            "push ds\n"
+            "push ebp\n"
+            "push edi\n"
+            "push esi\n"
+            "push edx\n"
+            "push ecx\n"
+            "push ebx\n"
+            "push esp\n" // Push stack pointer again (for variables and such idk)
+            "call [syscalls + eax * 4]\n" // Call syscall from table. Syscall number should be in eax
+            "add esp, 4\n"
+            "pop ebx\n" // Pop pushed values
+            "pop ecx\n"
+            "pop edx\n"
+            "pop esi\n"
+            "pop edi\n"
+            "pop ebp\n"
+            "pop ds\n"
+            "pop es\n"
+            "pop fs\n"
+            "pop gs\n"
+            "add esp, 4\n" // Save eax value
+            "iretd\n" // Return from interrupt
+
+            // TODO: Send an error or something here
+            "invalidSyscall:\n"
+            "iretd\n"
+
+            ".att_syntax" // Switch back to Att Syntax (Just in case)
+    );
+}
+
+#endif