Fixed bug in GDT length calculation in bootloader. Kernel now loads its own GDT so it doesn't clobber itself while touching memory. ATAPIO now loads its own copy of the boot sector so it isn't reliant on 0x7000 being mapped. Removed debug printf statements from a lot of places.

Makefile

@@ -2,7 +2,9 @@ CFLAGS = -m32 -mgeneral-regs-only -nostdlib -fno-builtin -fno-exceptions -fno-le
 LDFLAGS = 
 
 DISK_IMG_FILES = build/kernel/kernel.bin
-KERNEL_OBJS = build/c_code_entry.o build/kernel/screenstuff.o build/kernel/io.o build/kernel/idt.o build/kernel/keyboard.o build/kernel/strings.o build/kernel/atapio.o build/kernel/kernel.o build/kernel/paging.o build/kernel/allocate.o
+KERNEL_OBJS = build/kernel/entry.o build/kernel/screenstuff.o build/kernel/io.o build/kernel/idt.o build/kernel/keyboard.o \
+							build/kernel/strings.o build/kernel/atapio.o build/kernel/kernel.o build/kernel/paging.o build/kernel/allocate.o \
+							build/kernel/gdt.o
 STAGE2_OBS = build/c_code_entry.o build/boot_stage2/io.o build/boot_stage2/atapio.o build/boot_stage2/strings.o build/boot_stage2/screenstuff.o build/boot_stage2/stage2.o build/boot_stage2/paging.o
 
 run: disk.img
@@ -31,9 +33,14 @@ clean:
 build/boot/boot.bin: src/boot/boot.asm
 	nasm $< -o $@
 
+# Boot Stage 2
 build/boot_stage2/boot.bin: src/boot_stage2/boot_stage2.ld $(STAGE2_OBS)
 	ld $(LDFLAGS) -T $< $(STAGE2_OBS)
 
+build/boot_stage2/%.o: src/boot_stage2/%.c
+	gcc $(CFLAGS) -o $@ -c $<
+
+# Kernel
 build/kernel/kernel.bin: src/kernel/kernel.ld $(KERNEL_OBJS)
 	ld $(LDFLAGS) -T $< $(KERNEL_OBJS)
 
@@ -43,8 +50,9 @@ build/boot_stage2/stage2.o: src/boot_stage2/main.c
 build/kernel/%.o: src/kernel/%.c
 	gcc $(CFLAGS) -o $@ -c $<
 
-build/boot_stage2/%.o: src/boot_stage2/%.c
-	gcc $(CFLAGS) -o $@ -c $<
+build/kernel/%.o: src/kernel/%.asm
+	nasm -felf32 $< -o $@
 
+# Generic
 build/%.o: src/%.asm
 	nasm -felf32 $< -o $@

src/boot/boot.asm

@@ -134,7 +134,7 @@ data:
   db 0
 gdt_end:
 gdt_desc:
-  dw gdt_desc - gdt_end - 1
+  dw gdt_end - gdt - 1
   dd gdt
 
 TIMES 510 - ($ - $$) db 0

src/boot_stage2/main.c

@@ -107,7 +107,7 @@ void main() {
   PTE** kernel_page_tables = 0x521000;
 
   // Mark unavailable bitmap to 0x522000
-  mark_unavailble(bitmap, 0x522000 - (uint32_t)bitmap);
+  mark_unavailble(bitmap, 0x4000000);
 
   // Now we want to map some stuff.
   // But first, we should load the kernel somewhere
@@ -124,7 +124,7 @@ void main() {
   // Map the bitmap 
   map_many_4k_phys_to_virt(0x100000, 0xc0600000, kernel_page_directory, kernel_page_tables, 32);
 
-  map_many_4k_phys_to_virt(0x7000, 0x7000, kernel_page_directory, kernel_page_tables, 2);
+  map_4k_phys_to_virt(0x8000, 0x8000, kernel_page_directory, kernel_page_tables);
   map_many_4k_phys_to_virt(0x8a000, 0x8a000, kernel_page_directory, kernel_page_tables, 6);
 
   load_file("KERNEL  BIN", kernel_location);

src/kernel/allocate.c

@@ -57,7 +57,6 @@ void* dumb_alloc(uint32_t size) {
 
   while (size > 0) {
     for (; get_bit(last_free_page, bitmap) == 0; last_free_page++);
-    printf("Free page: %d\n", last_free_page);
 
     uint32_t phys_addr = last_free_page * 4096;
 

src/kernel/atapio.c

@@ -23,12 +23,14 @@ uint16_t sectorsPerFAT;
 void init_atapio() {
   rootDirEntries = (uint8_t*)dumb_alloc(8192);
   FAT1 = (uint16_t*)dumb_alloc(512 * 34);
-  printf("RDE: %x\nFAT1: %x\n", rootDirEntries, FAT1);
 
-  countReserved = *(uint16_t*)0x7c0e;
-  countFATs = *(uint8_t*)0x7c10;
-  countRDEs = *(uint16_t*)0x7c11;
-  sectorsPerFAT = *(uint16_t*)0x7c16;
+  uint32_t boot_sector = (uint32_t)dumb_alloc(4096);
+  read_sectors(0, 1, (uint8_t*)boot_sector);
+
+  countReserved = *((uint16_t*)(boot_sector + 0x0e));
+  countFATs = *((uint8_t*)(boot_sector + 0x10));
+  countRDEs = *((uint16_t*)(boot_sector + 0x11));
+  sectorsPerFAT = *((uint16_t*)(boot_sector + 0x16));
 
   // Select Drive 0 on the Primary Bus
   outb(0x1f6, 0xa0);

src/kernel/entry.asm

@@ -0,0 +1,6 @@
+[BITS 32]
+
+_start:
+  call main
+
+extern main

src/kernel/gdt.c

@@ -0,0 +1,76 @@
+#include "gdt.h"
+
+gdt_entry gdt[] = {
+  (gdt_entry){ // Null Segment
+    .limit_lo = 0,
+    .limit_hi = 0,
+    .base_lo = 0,
+    .base_mid = 0,
+    .base_hi = 0,
+    .accessed = 0,
+    .read_write = 0,
+    .direction = 0,
+    .executable = 0,
+    .system_segment = 0,
+    .privilege = 0,
+    .present = 0,
+    .size = 0,
+    .granularity = 0,
+
+    .__ignored__ = 0,
+  },
+  (gdt_entry){ // Code Segment
+    .limit_lo = 0xffff,
+    .limit_hi = 0xf,
+    .base_lo = 0,
+    .base_mid = 0,
+    .base_hi = 0,
+    .accessed = 0,
+    .read_write = 1,
+    .direction = 0,
+    .executable = 1,
+    .system_segment = 1,
+    .privilege = 0,
+    .present = 1,
+    .size = 1,
+    .granularity = 1,
+
+    .__ignored__ = 0,
+  },
+  (gdt_entry){ // Data Segment
+    .limit_lo = 0xffff,
+    .limit_hi = 0xf,
+    .base_lo = 0,
+    .base_mid = 0,
+    .base_hi = 0,
+    .accessed = 0,
+    .read_write = 1,
+    .direction = 0,
+    .executable = 0,
+    .system_segment = 1,
+    .privilege = 0,
+    .present = 1,
+
+    .size = 1,
+    .granularity = 1,
+
+    .__ignored__ = 0,
+  }
+};
+
+gdt_descr descr = (gdt_descr){
+  .size = sizeof(gdt) - 1,
+  .offset = gdt,
+};
+
+__attribute__((far)) void far_call() {}
+
+void init_gdt() {
+  asm volatile("lgdt %0;"
+               "mov $0x10, %%eax;"
+               "mov %%eax, %%ss;"
+               "mov $0x10, %%eax;"
+               "mov %%eax, %%ds" : : "m" (descr));
+  
+  far_call();
+}

src/kernel/gdt.h

@@ -0,0 +1,32 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include "types.h"
+
+typedef struct {
+  uint32_t limit_lo : 16;
+  uint32_t base_lo : 16;
+
+  uint32_t base_mid : 8;
+  uint32_t accessed : 1;
+  uint32_t read_write : 1;
+  uint32_t direction : 1;
+  uint32_t executable : 1;
+  uint32_t system_segment : 1;
+  uint32_t privilege : 2;
+  uint32_t present : 1;
+
+  uint32_t limit_hi : 4;
+  uint32_t __ignored__ : 2;
+  uint32_t size : 1;
+  uint32_t granularity : 1;
+  
+  uint32_t base_hi : 8;
+}__attribute__((packed)) gdt_entry;
+
+typedef struct {
+  uint16_t size;
+  uint32_t offset;
+}__attribute__((packed)) gdt_descr;
+
+#endif

src/kernel/kernel.c

@@ -5,11 +5,12 @@
 #include "keyboard.h"
 #include "strings.h"
 #include "atapio.h"
+#include "gdt.h"
 
 int main() {
+  init_gdt();
   init_idt();
   init_term();
-//  init_allocator();
 
   printf("Hello, World!\n\nWe are running XnoeOS Code in C now, Protected Mode has been achieved (as well as Virtual Memory / Paging!!!) and everything is working super nicely!\n\nHow wonderful!\n\nNow I just need to hope my print function works properly too~~\n");
   
@@ -20,19 +21,11 @@ int main() {
   enable_idt();
   init_atapio();
 
-  //while (1);
-
   uint8_t sector[512];
 
   read_sector(0, sector);
 
-  printf("OEM ID: %s\n", (char*)(sector+0x3));
-
-  char hellotxt[1024];
-
-  load_file("HELLO   TXT", hellotxt);
-  printf("%s", hellotxt);
-
+  uint8_t* filebuffer = (uint8_t*)dumb_alloc(0x3000);
 
   while (1) {
     printf(">>> ");
@@ -43,7 +36,6 @@ int main() {
 
     char* rest = split_on_first(' ', buffer);
 
-
     if (strcmp(buffer, "help", 4)) {
       printf(
         "XnoeOS 32 Bit Mode Help.\n"
@@ -64,7 +56,6 @@ int main() {
       printf("%s\n", rest);
     } else if (strcmp(buffer, "type", 4)) {
       char filenamebuffer[12];
-      uint8_t* filebuffer = 0x1006400;
 
       decode_filename(rest, filenamebuffer);
       if (!file_exists(filenamebuffer)) {
@@ -72,8 +63,8 @@ int main() {
         continue;
       }
 
-      for (int i=0; i<1024; i++)
-        hellotxt[i] = 0;
+      for (int i=0; i<4096; i++)
+        filebuffer[i] = 0;
       
       load_file(filenamebuffer, filebuffer);
       printf(filebuffer);

src/kernel/kernel.ld

@@ -7,9 +7,8 @@ SECTIONS {
   . = 0xc0000000;
 
   .text : { 
-    build/c_code_entry.o(.text)
+    build/kernel/entry.o(.text)
     build/kernel/kernel.o(.text)
     build/kernel/*(.text)
-    heap_section = .;
   }
 }