Basic implementation of system calls and usermode.

.gdbinit

@@ -0,0 +1,3 @@
+set osabi none
+target remote 127.0.0.1:1234
+symbol-file ./src/kitty.elf

src/Makefile

@@ -7,11 +7,21 @@ OBJ = ${C_SOURCES:.c=.o} ${ASM_SOURCES:.asm=.o}
 CFLAGS = -ffreestanding -fno-stack-protector -z execstack -no-pie -fno-pic
 
 ifeq ($(OS),Windows_NT)
-  host_os = windows
-  SHELL = cmd
-  CC = x86_64-elf-gcc
-  GDB = x86_64-elf-gdb
-  LD = x86_64-elf-ld
+  UNAME_S := $(shell uname -s)
+  ifeq ($(UNAME_S),MSYS_NT-10.0-22631)
+  	$(info MSYS2 detected)
+    host_os = linux
+    CC = gcc
+    GDB = gdb
+    LD = ld
+  else
+    $(info Windows detected)
+    host_os = windows
+    SHELL = cmd
+    CC = x86_64-elf-gcc
+    GDB = x86_64-elf-gdb
+    LD = x86_64-elf-ld
+  endif
 else
   UNAME_S := $(shell uname -s)
   ifeq ($(UNAME_S),Linux)
@@ -84,7 +94,7 @@ endif
 
 debug: os-image.bin kitty.elf # TODO needs work, change it so that a variable is added for break points
 #ifeq ($(host_os),windows)
-	qemu-system-x86_64 -s -S -fda os-image.bin
+	qemu-system-x86_64 -s -S -d int -fda os-image.bin
 #else ifeq ($(host_os),linux)
 #	qemu-system-x86_64 -s -S -fda os-image.bin &
 #endif

src/cpu/cpu_options.h

@@ -11,7 +11,7 @@
  *
  * Other defined variables in this file are for use with processor-specific compilation.
  *
- * All other CPU preprocessor definitions (for use in cpu cpu code) should be put in its corresponding header file.
+ * All other CPU preprocessor definitions (for use in cpu code) should be put in its corresponding header file.
  */
 
 #if CPU == 1 // x86_64 Processors

src/cpu/x86_64/gdt.asm

@@ -0,0 +1,47 @@
+; Access bits
+PRESENT        equ 1 << 7
+USER           equ 3 << 5
+NOT_SYS        equ 1 << 4
+EXEC           equ 1 << 3
+DC             equ 1 << 2
+RW             equ 1 << 1
+ACCESSED       equ 1 << 0
+
+; Flags bits
+GRAN_4K       equ 1 << 7
+SZ_32         equ 1 << 6
+LONG_MODE     equ 1 << 5
+global GDT
+GDT: ; 64 bit GDT, taken from https://wiki.osdev.org/Setting_Up_Long_Mode ; CC0 Licensing (Public Domain)
+    .Null: equ $ - GDT
+        dq 0
+    .Code: equ $ - GDT
+        dd 0xFFFF                                   ; Limit & Base (low, bits 0-15)
+        db 0                                        ; Base (mid, bits 16-23)
+        db PRESENT | NOT_SYS | EXEC | RW            ; Access
+        db GRAN_4K | LONG_MODE | 0xF                ; Flags & Limit (high, bits 16-19)
+        db 0                                        ; Base (high, bits 24-31)
+    .Data: equ $ - GDT
+        dd 0xFFFF                                   ; Limit & Base (low, bits 0-15)
+        db 0                                        ; Base (mid, bits 16-23)
+        db PRESENT | NOT_SYS | RW                   ; Access
+        db GRAN_4K | SZ_32 | 0xF                    ; Flags & Limit (high, bits 16-19)
+        db 0                                        ; Base (high, bits 24-31)
+    .UserCode: equ $ - GDT
+        dd 0xFFFF                                   ; Limit & Base (low, bits 0-15)
+        db 0                                        ; Base (mid, bits 16-23)
+        db PRESENT | USER | NOT_SYS | EXEC | RW ; 0xFA     ; Access
+        db GRAN_4K | LONG_MODE | 0xF                ; Flags & Limit (high, bits 16-19)
+        db 0                                        ; Base (high, bits 24-31)
+    .UserData: equ $ - GDT
+        dd 0xFFFF                                   ; Limit & Base (low, bits 0-15)
+        db 0                                        ; Base (mid, bits 16-23)
+        db PRESENT | USER | NOT_SYS | RW ;0xF2 ;             ; Access
+        db GRAN_4K | SZ_32 | 0xF                    ; Flags & Limit (high, bits 16-19)
+        db 0                                        ; Base (high, bits 24-31)
+    .TSS: equ $ - GDT
+        dq 0x0000000000000000
+        dq 0x0000000000000000
+    .Pointer:
+        dw $ - GDT - 1
+        dq GDT

src/cpu/x86_64/gdt.h

@@ -0,0 +1,26 @@
+//
+// Created by AIDAN on 9/26/2024.
+//
+
+#ifndef KITTY_GDT_H
+#define KITTY_GDT_H
+
+#include "stdint.h"
+
+struct global_descriptor_table {
+    uint64_t null;
+    uint64_t code;
+    uint64_t data;
+    uint64_t user_code;
+    uint64_t user_data;
+    uint32_t tss_0;
+    uint32_t tss_1;
+    uint32_t tss_2;
+    uint32_t tss_3;
+    uint16_t size;
+    uint64_t offset;
+}__attribute__ ((packed));
+
+extern struct global_descriptor_table GDT;
+
+#endif //KITTY_GDT_H