src/kernel/boot.S

@@ -50,3 +50,29 @@ _start:
 	
 
 .include "./src/kernel/gdt/gdt.s"
+
+	loadIDT:
+		#load idt
+		call init_idt
+        sti
+        
+        # Try enable A20
+		# mov $0x2401, %ax
+		# int $0x15
+
+
+		# enable protected mode
+		mov %cr0, %eax 
+		or $1, %eax
+		mov %eax, %cr0
+
+		
+		call kernel_main
+
+
+		cli
+	1:	hlt
+		jmp 1b
+
+
+.size _start, . - _start

src/kernel/gdt/gdt.s

@@ -1,75 +1,19 @@
-/* Tell processor to use our gdt*/
+.global LoadGlobalDescriptorTable
-gdt: 
-    .word (gdt_end - gdt_start -1) # Size of the GDT in bytes minus 1 for math reasons
-    .int gdt_start # linear address of our GDT
 
+	LoadGlobalDescriptorTable:
+		lgdt gdtDescriptor
 
-.att_syntax
+		movw $16, %ax 
-
-.global load_gdt
-	load_gdt:
-		lgdt gdt
-
-		# set the segment selecters
-
-		movw $0x10, %ax 
 		movw %ax, %ds
 		movw %ax, %es
 		movw %ax, %fs
 		movw %ax, %gs
 		movw %ax, %ss
-		ljmp $0x08, $flush 
+		
+		jmp $8,$flush 
 
 		flush: 
+		ret
 		
 	
-		#load idt
-		call init_idt
-        sti
 
-        # Try enable A20
-		# mov $0x2401, %ax
-		# int $0x15
-
-
-		# enable protected mode
-		mov %cr0, %eax 
-		or $1, %eax
-		mov %eax, %cr0
-
-		
-		call kernel_main
-
-
-		cli
-	1:	hlt
-		jmp 1b
-
-
-.size _start, . - _start
-
-/*
-* Create the GDT
-*/
-.section .data
-gdt_start:
-gdt_null:
-.long 0x0
-.long 0x0
-
-gdt_kcode:
-.word 0xFFFF             # limit
-.word 0x0                # base
-.byte 0x0                # base
-.byte 0b10011010         # 1st flags | type flags
-.byte 0b11001111         # 2nd flags | limit
-.byte 0x0                # base
-
-gdt_kdata:
-.word 0xFFFF             # limit
-.word 0x0                # base
-.byte 0x0                # base
-.byte 0b10010010         # 1st flags | type flags
-.byte 0b11001111         # 2nd flags | limit
-.byte 0x0                # base
-gdt_end:

src/kernel/gdt/gdtc.cpp

@@ -1,31 +1,61 @@
 #include "gdtc.h"
 #include "../tty/kterm.h"
 
-gdtEntry_t gdt[3];
+#define NULL_SEGMENT          0
-gdtSegmentPointer gdtPointer{};
+#define KERNEL_CODE_SEGMENT   1
+#define KERNEL_DATA_SEGMENT   2
+#define USER_CODE_SEGMENT     3
+#define USER_DATA_SEGMENT     4
+
+SegmentDescriptor GlobalDescriptorTable[5];
+GlobalDescriptorTableDescriptor gdtDescriptor;
+
+void add_descriptor(int which , unsigned long base, unsigned long limit, unsigned char access, unsigned char granularity ){
+   GlobalDescriptorTable[which].base_low = (base & 0xFFFF );
+   GlobalDescriptorTable[which].base_middle = (base >> 6) & 0xFF;
+   GlobalDescriptorTable[which].base_high = (base >> 24) & 0xFF;
+   
+   GlobalDescriptorTable[which].limit_low = (limit & 0xFFFF);
+   GlobalDescriptorTable[which].granularity = ((limit >> 16) & 0x0F);
+
+   GlobalDescriptorTable[which].granularity |= (granularity & 0xF0);
+   GlobalDescriptorTable[which].access = access;
 
 
-
-void gdtSetGate(int num, uint64_t base, uint64_t limit, uint8_t access,
-   uint8_t gran){
-   gdt[num].lBase      = (base & 0xFFFF);
-   gdt[num].mBase      = (base >> 16) & 0xFF;
-   gdt[num].hBase      = (base >> 24) & 0xFF;
-
-   gdt[num].lLimit      = (limit & 0xFFFF);
-   gdt[num].granularity   = ((limit >> 16) & 0x0F);
-
-   gdt[num].granularity   |= (gran & 0xF0);
-   gdt[num].access      = access;
 }
 
-void setupGdt(){
-   gdtPointer.limit   = (sizeof(gdtEntry_t) * 3) - 1;
-   gdtPointer.base    = (uint32_t) &gdt;
 
-   gdtSetGate(0, 0, 0, 0, 0);
+
-   gdtSetGate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+
-   gdtSetGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
+void initGDT(){
-   printf("call to load gdt\n");
+
-   load_gdt();
+      // NULL segment
+      add_descriptor(NULL_SEGMENT, 0,0,0,0);
+
+      // Kernel Code Segment
+      add_descriptor(KERNEL_CODE_SEGMENT, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+
+      // Kernel Data Segment
+      add_descriptor(KERNEL_DATA_SEGMENT, 0, 0xFFFFFFFF, 0x92, 0xCF);      
+
+      // User Code Segment
+      // TODO:
+      
+      // User Data Segement
+      // TODO: 
+      
+      // init Gdt Descriptor
+      gdtDescriptor.limit = ((sizeof(SegmentDescriptor ) * 5 ) - 1);
+      gdtDescriptor.base = (unsigned int) &GlobalDescriptorTable;
+
+
+
+      LoadGlobalDescriptorTable();
+
+      while (true)
+         asm volatile("hlt");
+      
+
+
+
 }

src/kernel/gdt/gdtc.h

@@ -1,22 +1,27 @@
 #include <stdint.h>
-extern "C"{
 
-typedef struct {
-   uint16_t           lLimit;
-   uint16_t           lBase;
-   uint8_t            mBase;
-   uint8_t            access;
-   uint8_t            granularity;
-   uint8_t            hBase;
-} gdtEntry_t;
 
-struct gdtSegmentPointer {
+struct SegmentDescriptor {
-   uint16_t limit;
+   unsigned short limit_low;
-   uint32_t base;
+   unsigned short base_low;
-};
+   unsigned char base_middle;
+   unsigned char access;
+   unsigned char granularity;
+   unsigned char base_high;
+}__attribute__((packed));
 
-extern gdtSegmentPointer gdtPointer;
 
-extern void load_gdt();
+struct GlobalDescriptorTableDescriptor{
-void setupGdt();
+   unsigned short limit;
-}
+   unsigned int base;
+}__attribute__((packed));
+
+extern SegmentDescriptor GlobalDescriptorTable[];
+extern GlobalDescriptorTableDescriptor gdtDescriptor;
+
+
+void add_descriptor(int which , unsigned long base, unsigned long limit, unsigned char access, unsigned char granularity );
+
+
+extern "C" void LoadGlobalDescriptorTable();
+void initGDT();

src/kernel/kernel.cpp

@@ -26,8 +26,7 @@
             printf("kernel: 0x%x - 0x%x\n", &kernel_begin , &kernel_end);         
         }
 
-        printf("Call to setupGdt!\n");
+        initGDT();
-        setupGdt();
 
        
     }