Kernel: add early_kernel and GDT

TODO.org

@@ -10,10 +10,11 @@
 ** TODO Improve Build
    * [ ] Add arguments 
 ** TODO Global Constructors Table
-   * [ ] Init GDT in early kernel
+   * [X] Init GDT in early kernel
    * [ ] Add LDT (Local Descriptor Table)
 ** TODO Serial
    * [ ] Print debuging messages to Serial
+   * [ ] Add more arguments to serial_printf function
    * [ ] Add input from Serial
 ** TODO Interrupt Description Table
    * [ ] Init IDT in early kernel

kernel/Makefile

@@ -29,6 +29,7 @@ LIBS:=$(LIBS) $(KERNEL_ARCH_LIBS)
 
 KERNEL_OBJS=\
 $(KERNEL_ARCH_OBJS) \
+kernel/early_kernel.o \
 kernel/kernel.o \
 
 OBJS=\

kernel/arch/i386/boot.S

@@ -29,6 +29,9 @@ _start:
 	# Call the global constructors.
 	call _init
 
+	# Call early kernel (init GDT, IDT and other)
+	call kernel_early_main
+	
 	# Transfer control to the main kernel.
 	call kernel_main
 
@@ -37,3 +40,19 @@ _start:
 1:	hlt
 	jmp 1b
 .size _start, . - _start
+
+.global gdt_flush
+gdt_flush:
+	cli
+	mov    0x4(%esp),%eax
+        sgdtl  (%eax)
+        mov    $0x10,%ax
+        mov    %eax,%ds
+        mov    %eax,%es
+        mov    %eax,%fs
+        mov    %eax,%gs
+        mov    %eax,%ss
+        ljmp   $0x8,$.flush
+.flush:
+	ret
+

kernel/kernel/early_kernel.c

@@ -0,0 +1,12 @@
+#include <stdint.h>
+
+#include <kernel/tty.h>
+#include "serial.h"
+#include "gdt.c"
+
+void kernel_early_main(void) {
+  gdt_init();
+  terminal_initialize();
+  init_serial();
+  serial_printf("gdt initialized!\n");
+}

kernel/kernel/gdt.c

@@ -0,0 +1,108 @@
+
+// Used for creating GDT segment descriptors in 64-bit integer form.
+ 
+#include <stdio.h>
+#include <stdint.h>
+ 
+// Each define here is for a specific flag in the descriptor.
+// Refer to the intel documentation for a description of what each one does.
+#define SEG_DESCTYPE(x)  ((x) << 0x04) // Descriptor type (0 for system, 1 for code/data)
+#define SEG_PRES(x)      ((x) << 0x07) // Present
+#define SEG_SAVL(x)      ((x) << 0x0C) // Available for system use
+#define SEG_LONG(x)      ((x) << 0x0D) // Long mode
+#define SEG_SIZE(x)      ((x) << 0x0E) // Size (0 for 16-bit, 1 for 32)
+#define SEG_GRAN(x)      ((x) << 0x0F) // Granularity (0 for 1B - 1MB, 1 for 4KB - 4GB)
+#define SEG_PRIV(x)     (((x) &  0x03) << 0x05)   // Set privilege level (0 - 3)
+ 
+#define SEG_DATA_RD        0x00 // Read-Only
+#define SEG_DATA_RDA       0x01 // Read-Only, accessed
+#define SEG_DATA_RDWR      0x02 // Read/Write
+#define SEG_DATA_RDWRA     0x03 // Read/Write, accessed
+#define SEG_DATA_RDEXPD    0x04 // Read-Only, expand-down
+#define SEG_DATA_RDEXPDA   0x05 // Read-Only, expand-down, accessed
+#define SEG_DATA_RDWREXPD  0x06 // Read/Write, expand-down
+#define SEG_DATA_RDWREXPDA 0x07 // Read/Write, expand-down, accessed
+#define SEG_CODE_EX        0x08 // Execute-Only
+#define SEG_CODE_EXA       0x09 // Execute-Only, accessed
+#define SEG_CODE_EXRD      0x0A // Execute/Read
+#define SEG_CODE_EXRDA     0x0B // Execute/Read, accessed
+#define SEG_CODE_EXC       0x0C // Execute-Only, conforming
+#define SEG_CODE_EXCA      0x0D // Execute-Only, conforming, accessed
+#define SEG_CODE_EXRDC     0x0E // Execute/Read, conforming
+#define SEG_CODE_EXRDCA    0x0F // Execute/Read, conforming, accessed
+ 
+#define GDT_CODE_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(0)     | SEG_CODE_EXRD
+ 
+#define GDT_DATA_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(0)     | SEG_DATA_RDWR
+ 
+#define GDT_CODE_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(3)     | SEG_CODE_EXRD
+ 
+#define GDT_DATA_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(3)     | SEG_DATA_RDWR
+#define GDT_MAX_DESCRIPTORS 3
+
+struct gdt_entry {
+  uint16_t limit_low;
+  uint16_t base_low;
+  uint8_t base_middle;
+  uint8_t access;
+  uint8_t granularity;
+  uint8_t base_high;
+}__attribute__((packed));
+
+struct gdt_ptr {
+  uint16_t limit;
+  uint32_t base;
+}__attribute__((packed));
+
+struct gdt_entry gdt[GDT_MAX_DESCRIPTORS];
+struct gdt_ptr gp;
+
+extern void gdt_flush(struct gdt_ptr* gdt_ptr_addr);
+
+void
+create_descriptor(uint32_t base, uint32_t limit, uint16_t flag)
+{
+    uint64_t descriptor;
+ 
+    // Create the high 32 bit segment
+    descriptor  =  limit       & 0x000F0000;         // set limit bits 19:16
+    descriptor |= (flag <<  8) & 0x00F0FF00;         // set type, p, dpl, s, g, d/b, l and avl fields
+    descriptor |= (base >> 16) & 0x000000FF;         // set base bits 23:16
+    descriptor |=  base        & 0xFF000000;         // set base bits 31:24
+ 
+    // Shift by 32 to allow for low part of segment
+    descriptor <<= 32;
+ 
+    // Create the low 32 bit segment
+    descriptor |= base  << 16;                       // set base bits 15:0
+    descriptor |= limit  & 0x0000FFFF;               // set limit bits 15:0
+ 
+    printf("0x%.16llX\n", descriptor);
+}
+
+void gdt_init() {
+  gp.limit = (sizeof(struct gdt_entry) * GDT_MAX_DESCRIPTORS) - 1;
+  gp.base = (uint32_t) &gdt;
+
+  create_descriptor(0, 0, 0);
+  create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0));
+  create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0));
+  create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3));
+  create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3));
+
+  /*
+  gdt_set_gate(0, 0, 0, 0, 0);
+  gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+  gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
+  */
+  
+  gdt_flush(&gp);
+}

kernel/kernel/kernel.c

@@ -1,13 +1,6 @@
-#define PORT 0x3f8
-
 #include <stdio.h>
 
-#include <kernel/tty.h>
-#include "serial.h"
-
 void kernel_main(void) {
-	terminal_initialize();
-	init_serial();
 	printf("Hello from OrionOS!\n");
 	printf("Testing serial\n");
 	serial_printf("Test is success!\n");