Adding gdt

4 files changed, 70 insertions, 9 deletions

diff --git a/Makefile b/Makefile
index 86585c5..b427918 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,7 @@ ISO_DIR=isodir
 
 TARGET=myos
 
-OBJ_FILES=boot.o kernel.o
+OBJ_FILES=boot.o kernel.o gdt.o
 CRTBEGIN_OBJ=$(shell $(CC) -print-file-name=crtbegin.o)
 CRTEND_OBJ=$(shell $(CC) -print-file-name=crtend.o)
 OBJ=$(BUILD_DIR)/crti.o $(CRTBEGIN_OBJ) $(patsubst %,$(BUILD_DIR)/%,$(OBJ_FILES)) $(CRTEND_OBJ) $(BUILD_DIR)/crtn.o
diff --git a/src/boot.s b/src/boot.s
index 385ee70..a0f0c2e 100644
--- a/src/boot.s
+++ b/src/boot.s
@@ -9,7 +9,15 @@
 .long MAGIC
 .long FLAGS
 .long CHECKSUM
- 
+
+.global _start
+.global load_gdt
+
+load_gdt:
+    movl 4(%esp), %edx
+    lgdt (%edx)
+    ret
+
 .section .bss
 .align 16
 stack_bottom:
@@ -17,15 +25,19 @@ stack_bottom:
 stack_top:
 
 .section .text
-.global _start
 .type _start, @function
 _start:
+	call init_gdt_table
+	mov 0x10, %ax
+	mov %ds, %ax
+	mov %es, %ax
+	mov %fs, %ax
+	mov %gs, %ax
+	mov %ss, %ax
 	mov $stack_top, %esp
- 
+	cli
 	call _init
 	call kernel_main
- 
-	cli
 1:	hlt
 	jmp 1b
  
diff --git a/src/gdt.c b/src/gdt.c
new file mode 100644
index 0000000..9f87032
--- /dev/null
+++ b/src/gdt.c
@@ -0,0 +1,49 @@
+#include<stdbool.h>
+#include<stddef.h>
+#include<stdint.h>
+
+struct gdt_entry
+{
+    uint16_t limit;
+    uint16_t base1;
+    uint8_t base2;
+    uint8_t access;
+    uint8_t limit_flags;
+    uint8_t base3;
+} __attribute__((packed));
+
+struct gdt_pointer
+{
+    uint16_t size;
+    uint32_t offset;
+} __attribute__((packed));
+
+// asm function
+extern void load_gdt(struct gdt_pointer *gdtp);
+
+struct gdt_entry gdt[3];
+struct gdt_pointer gdtp;
+
+void init_gdt_entry(size_t num, uint32_t limit, uint32_t base1, uint32_t base2, uint8_t access, uint8_t limit_flags, uint8_t base3)
+{
+    gdt[num].limit=limit;
+    gdt[num].base1=base1;
+    gdt[num].access=access;
+    gdt[num].limit_flags=limit_flags;
+    gdt[num].base3=base3;
+}
+
+void init_gdt_table()
+{
+    gdtp.size=sizeof(gdt)-1;
+    gdtp.offset=(uint32_t)&gdt;
+
+    //null
+    init_gdt_entry(0,0,0,0,0,0,0);
+    //code
+    init_gdt_entry(1,0xffff,0x0000,0x00,0b10011010,0b11001111,0x00);
+    //data
+    init_gdt_entry(2,0xffff,0x0000,0x00,0b10010010,0b11001111,0x00);
+
+    load_gdt(&gdtp);
+}
diff --git a/src/kernel.c b/src/kernel.c
index 90f34bd..c6d1045 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -1,6 +1,6 @@
-#include <stdbool.h>
-#include <stddef.h>
-#include <stdint.h>
+#include<stdbool.h>
+#include<stddef.h>
+#include<stdint.h>
 #include"vga.h"
 
 static const size_t VGA_WIDTH = 80;