Paging

.gitignore

@@ -1,3 +1,4 @@
 *.iso
 isodir
 sysroot
+.vscode/

README.md

@@ -5,8 +5,31 @@ Welcome to rockOS project, a hobby OS that aims to run rogue and nethack.
 - GDT
 - IDT
 - PIC initialization
-- Semi-working keyboard driver
-- Paging initialization
+- PIT timer
+- Keyboard driver
+- Bitmap paging
+
+
+## Usage
+Just grab the latest ISO from the releases and run it on a virtual machine
+such as QEMU or Virtualbox, bare-metal not tested.
+
+## Build
+### Dependencies
+- a decent compiler such as gcc or clang
+- grub2 (if under GNU/Linux)
+- xorriso
+- make
+- tar (for compiling the toolchain)
+- wget/curl (for compiling the toolchain)
+
+If it is your first time building, you need to compile the toolchain first.
+For that, you just need to run build-toolchain.sh, which will download binutils,
+gcc, grub if youre on macOS, and then compile them to $HOME/opt/cross-i686 by default
+which can be changed from the prompt.
+
+After you compiled the toolchain and added $PREFIX/bin to your PATH as instructed by the script,
+you can run qemu.sh to compile and open the OS on QEMU or iso.sh to just generate the ISO.
 
 
 ## Credits
@@ -15,7 +38,7 @@ Welcome to rockOS project, a hobby OS that aims to run rogue and nethack.
 
 
 ## Acknowledgements
-- osdev.org community for huge documentation on osdev
+- osdev.org community for huge documentation on OS Development
 - musl for libc implementation
 
 

build-toolchain.sh

@@ -1,7 +1,8 @@
 #!/bin/sh
 #export PREFIX="$HOME/opt/cross-i686"
 
-echo "Welcome to rockOS toolchain compilation script, where would you like to install your toolchain?\nLeave blank for $HOME/opt/cross-i686"
+echo "Welcome to rockOS toolchain compilation script, where would you like to install your toolchain?"
+echo "Leave blank for $HOME/opt/cross-i686"
 
 read PREFIX
 
@@ -9,6 +10,10 @@ if [ "$PREFIX" == "" ]; then
     export PREFIX="$HOME/opt/cross-i686"
 fi
 
+echo "This is the location you chose: $PREFIX"
+echo "Press Enter to continue"
+read continue
+
 mkdir -p "$PREFIX"
 export TARGET=i686-elf
 export PATH="$PREFIX/bin:$PATH"

kernel/include/rockos/paging.h

@@ -16,10 +16,16 @@
  *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+#include <stdint.h>
+
 #ifndef _ROCKOS_PAGING_H
 #define _ROCKOS_PAGING_H
 
 #define PAGE_ENTRIES 1024
-#define PAGE_SIZE 4 * PAGE_ENTRIES
+#define PAGE_SIZE 4096
+
+uint32_t* get_page();
+void set_page_free(uint32_t*);
+uint32_t get_used_memsize();
 
 #endif

kernel/rockos/kernel.c

@@ -5,6 +5,7 @@
 #include <rockos/pic.h>
 #include <rockos/hal.h>
 #include <rockos/timer.h>
+#include <rockos/paging.h>
 
 void kernel_main(void) {
     printf("Hello, kernel World!\n");
@@ -15,13 +16,34 @@ void kernel_main(void) {
     printf("And now for 0.1 + 0.2...... which is: %.17f\n", 0.1 + 0.2);
     initialize_keyset();
     
-    outb(0x70, (0x80 << 7) | 0x0); // Seconds
+    outb(0x70, 0x0); // Seconds
     uint8_t sec = inb(0x71);
-    outb(0x70, (0x80 << 7) | 0x02); // Minutes
+    outb(0x70, 0x02); // Minutes
     uint8_t min = inb(0x71);
-    outb(0x70, (0x80 << 7) | 0x04); // Hours
+    outb(0x70, 0x04); // Hours
     uint8_t hour = inb(0x71);
-    printf("Time: %x:%x:%x\n", hour, min, sec);
+    // BCD to binary conversion
+    sec = (sec & 0x0F) + ((sec / 16) * 10);
+    min = (min & 0x0F) + ((min / 16) * 10);
+    hour = ((hour & 0x0F) + (((hour & 0x70) / 16) * 10)) | (hour & 0x80);
+    printf("Time: %02d:%02d:%02d UTC+3\n", (hour + 3) % 24, min, sec);
+
+    uint32_t first = get_used_memsize();
+    uint32_t limit = 1024 * 8;
+    uint32_t* pages[limit];
+
+    for(uint32_t i = 0; i < limit; i++) {
+        pages[i] = get_page();
+    }
+    uint32_t middle = get_used_memsize();
+
+    for(uint32_t i = 0; i < limit; i++) {
+        set_page_free(pages[i]);
+    }
+    uint32_t last = get_used_memsize();
+    
+    printf("Before Allocation: %d KiB\nAfter allocation: %d KiB\nAfter Clear: %d KiB\n", first, middle, last);
+    printf("Finished!\n");
 
     unsigned char key;
     for(;;) {

kernel/rockos/paging.c

@@ -18,24 +18,80 @@ void enable_paging() {
     );
 }
 
+static uint32_t page_dir[PAGE_ENTRIES] __attribute__((aligned(PAGE_SIZE)));
+static uint32_t first_page_table[PAGE_ENTRIES] __attribute__((aligned(PAGE_SIZE)));
+
 void paging_init() {
-    uint32_t page_dir[PAGE_ENTRIES] __attribute__((aligned(PAGE_SIZE)));
     for(int i = 0; i < PAGE_ENTRIES; i++) {
         // Supervisor: only kernel-mode can access
         // Write Enabled: Can be both read and written to
         // Not Present: Page table not present
         page_dir[i] = 0x00000002;
     }
-
-    uint32_t first_page_table[PAGE_ENTRIES] __attribute__((aligned(PAGE_SIZE)));
+    
     for(unsigned int i = 0; i < PAGE_ENTRIES; i++) {
         // As the address is page aligned, it will leave 12 bits zeroed,
         // which are used by the attributes.
-        first_page_table[i] = (i * 0x1000) | 3; // attr: supervisor, r/w, present
+        first_page_table[i] = (i * 0x1000) | 0x103; // attr: supervisor, r/w, present, 9th bit set
     }
 
     page_dir[0] = ((unsigned int)first_page_table) | 3; //attr: supervisor, r/w, present
 
     load_page_dir(page_dir);
     enable_paging();
+}
+
+uint32_t* get_page() {
+    // Search directories for tables
+    for (int i = 0; i < PAGE_ENTRIES; ++i) {
+        // If table is found (if 2nd and 1st bit are set)
+        if((page_dir[i] & 0x3) == 0x3) {
+            // Cast table location
+            uint32_t *mytable = (uint32_t*)((page_dir[i] >> 12) << 12);
+            // Search table for pages
+            for(int j = 0; j < PAGE_ENTRIES; ++j) {
+                // If page is found (9th, 2nd, 1st bit set)
+                if((mytable[j] & 0x103) == 0x103) {
+                    mytable[j] &= ~0x100; // Unset 9th bit
+                    return &mytable[j];
+                }
+            } // No page found till last entry
+            // Check if next table is not initialized
+            if((page_dir[i+1] & 0x3) != 0x3) {
+                // The last page of previous table points to the next table
+                uint32_t *newtable = &mytable[2*PAGE_ENTRIES];
+                for(int k = 0; k < PAGE_ENTRIES; ++k) {
+                    newtable[k] = (k * 0x1000) | 0x103; // attr: supervisor, r/w, present, 9th bit set
+                }
+                page_dir[i+1] = ((unsigned int)newtable) | 3; //attr: supervisor, r/w, present
+            }
+        }
+    }
+    return 0;
+}
+
+void set_page_free(uint32_t* addr) {
+    // Set 9th, 2nd and 1st bits
+    *(addr) |= 0x103;
+}
+
+uint32_t get_used_memsize() {
+    uint32_t used = 0;
+    // Iterate over page_dirs
+    for(int i = 0; i < PAGE_ENTRIES; ++i) {
+        // If a table is available
+        if((page_dir[i] & 3) == 3) {
+            // Cast the table
+            uint32_t* table = ((page_dir[i] >> 12) << 12);
+            // Iterate over table
+            for(int j = 0; j < PAGE_ENTRIES; ++j) {
+                // If a page is unavailable
+                if((table[j] & 0x103) != 0x103) {
+                    // Then it is used
+                    used += 4*4;
+                }
+            }
+        }
+    }
+    return used;
 }