gdt working

kernel/Makefile

@@ -1,23 +1,14 @@
-
 OSNAME = CustomOS
 
 GNUEFI = ../gnu-efi
 OVMFDIR = ../OVMFbin
 LDS = kernel.ld
 CC = gcc
+ASMC = nasm
 LD = ld
 
 CFLAGS = -ffreestanding -fshort-wchar
-LDFLAGS = -T $(LDS) -static -Bsymbolic -nostdlib
-OSNAME = CustomOS
-
-GNUEFI = ../gnu-efi
-OVMFDIR = ../OVMFbin
-LDS = kernel.ld
-CC = gcc
-LD = ld
-
-CFLAGS = -ffreestanding -fshort-wchar 
+ASMFLAGS = 
 LDFLAGS = -T $(LDS) -static -Bsymbolic -nostdlib
 
 SRCDIR := src
@@ -27,8 +18,10 @@ BOOTEFI := $(GNUEFI)/x86_64/bootloader/main.efi
 
 rwildcard=$(foreach d,$(wildcard $(1:=/*)),$(call rwildcard,$d,$2) $(filter $(subst *,%,$2),$d))
 
-SRC = $(call rwildcard,$(SRCDIR),*.cpp)          
+SRC = $(call rwildcard,$(SRCDIR),*.cpp)  
+ASMSRC = $(call rwildcard,$(SRCDIR),*.asm)  
 OBJS = $(patsubst $(SRCDIR)/%.cpp, $(OBJDIR)/%.o, $(SRC))
+OBJS += $(patsubst $(SRCDIR)/%.asm, $(OBJDIR)/%_asm.o, $(ASMSRC))
 DIRS = $(wildcard $(SRCDIR)/*)
 
 kernel: $(OBJS) link
@@ -38,9 +31,13 @@ $(OBJDIR)/%.o: $(SRCDIR)/%.cpp
 	@ mkdir -p $(@D)
 	$(CC) $(CFLAGS) -c $^ -o $@
 	
+$(OBJDIR)/%_asm.o: $(SRCDIR)/%.asm
+	@ echo !==== ASSEMBLING $^
+	@ mkdir -p $(@D)
+	$(ASMC) $(ASMFLAGS) $^ -f elf64 -o $@
+	 
 link:
 	@ echo !==== LINKING
-	@echo $(OBJS)
 	$(LD) $(LDFLAGS) -o $(BUILDDIR)/kernel.elf $(OBJS)
 
 setup:

kernel/src/gdt/gdt.asm

@@ -0,0 +1,23 @@
+[bits 64]
+LoadGDT:
+	; rdi is the first argument passed to the LoadGDT function by C
+	lgdt [rdi]
+
+	; update the data segment registers
+	mov ax, 0x10
+	mov ds, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+	mov ss, ax
+
+	; update the code segment
+	pop rdi ; store return address in rdi
+	mov rax, 0x08 ; code segment offset
+	push rax ; we push 0x08 because it will be used by the far return instruction
+	push rdi ; push return address because it will be used by far return
+
+	; far return
+	retfq
+	
+GLOBAL LoadGDT

kernel/src/gdt/gdt.cpp

@@ -0,0 +1,11 @@
+#include "gdt.h"
+
+__attribute__((aligned(0x1000)))
+GDT DefaultGDT = {
+	{0, 0, 0, 0x00, 0x00, 0}, // null
+	{0, 0, 0, 0x9A, 0xA0, 0}, // kernel code
+	{0, 0, 0, 0x92, 0xA0, 0}, // kernel data
+	{0, 0, 0, 0x00, 0x00, 0}, // user null
+	{0, 0, 0, 0x9A, 0xA0, 0}, // user code
+	{0, 0, 0, 0x92, 0xA0, 0}, // user data
+};

kernel/src/gdt/gdt.h

@@ -0,0 +1,29 @@
+#pragma once
+#include <stdint.h>
+
+struct GDTDescriptor {
+	uint16_t Size;
+	uint64_t Offset;
+}__attribute__((packed));
+
+struct GDTEntry {
+	uint16_t Limit0;
+	uint16_t Base0;
+	uint8_t Base1;
+	uint8_t AccessByte;
+	uint8_t Limit1_Flags;
+	uint8_t Base2;
+}__attribute__((packed));
+
+struct GDT {
+	GDTEntry Null; // 0x00
+	GDTEntry KernelCode; // 0x08
+	GDTEntry KernelData; // 0x10
+	GDTEntry UserNull; // 0x18
+	GDTEntry UserCode; // 0x20
+	GDTEntry UserData; // 0x28
+}__attribute__((packed)) __attribute__((aligned(0x1000)));
+
+extern GDT DefaultGDT;
+
+extern "C" void LoadGDT(GDTDescriptor* gdtDescriptor);

kernel/src/kernelUtil.cpp

@@ -5,6 +5,7 @@ extern "C" void __stack_chk_fail(void) {
 }
 
 #include "kernelUtil.h"
+#include "gdt/gdt.h"
 
 KernelInfo kernelInfo;
 PageTableManager pageTableManager = NULL;
@@ -43,6 +44,11 @@ void PrepareMemory(BootInfo* bootInfo){
 
 KernelInfo InitializeKernel(BootInfo* bootInfo){
 
+	GDTDescriptor gdtDescriptor;
+	gdtDescriptor.Size = sizeof(GDT) - 1;
+	gdtDescriptor.Offset = (uint64_t)&DefaultGDT;
+	LoadGDT(&gdtDescriptor);
+
     PrepareMemory(bootInfo);
 
     memset(bootInfo->framebuffer->BaseAddress, 0, bootInfo->framebuffer->BufferSize);