From 7e3279dba105f7ad5b0308392e3b7519d4c6757c Mon Sep 17 00:00:00 2001
From: g1n <g1n@ttm.sh>
Date: Sat, 12 Feb 2022 16:03:42 +0200
Subject: [PATCH] Added page frame allocator

Currently it is using bitmap. Maybe will be rewriten. Also
deallocator is needed
---
 src/include/paging.h |  7 ++++++
 src/kernel.c         |  5 -----
 src/paging.c         | 51 ++++++++++++++++++++++++++++++++++++--------
 3 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/src/include/paging.h b/src/include/paging.h
index c12ac83..5208218 100644
--- a/src/include/paging.h
+++ b/src/include/paging.h
@@ -3,6 +3,13 @@
 
 #include <idt.h>
 
+#define NPAGES 4096U // FIXME
+#define ENTRY_WIDTH 32U
+#define PAGE_SIZE 0x1000U
+
+typedef uint32_t page_addr_t;
+
+page_addr_t kalloc_frame();
 void paging_init();
 void page_fault(registers_t regs);
 
diff --git a/src/kernel.c b/src/kernel.c
index 12f7aab..46d3c21 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -6,9 +6,4 @@
 void kernel_main() {
   kprintf("Hello, World!\n");
   dbgf("Hello serial World!\n");
-  warn("test warning debug %d\n", 42);
-  error("test error debug %d\n", 42);
-  fixme("test fixme debug %d\n", 42);
-  todo("test todo debug %d\n", 42);
-  panic("test panic\n");
 }
diff --git a/src/paging.c b/src/paging.c
index 014add4..b148241 100644
--- a/src/paging.c
+++ b/src/paging.c
@@ -2,8 +2,10 @@
 #include <stdio.h>
 #include <string.h>
 
-uint32_t page_directory[1024] __attribute__((aligned(4096)));
-uint32_t first_page_table[1024] __attribute__((aligned(4096)));
+uint32_t page_dir[1024] __attribute__((aligned(4096)));
+uint32_t page_table[1024] __attribute__((aligned(4096)));
+
+static uint32_t bitmap[NPAGES/ENTRY_WIDTH] __attribute__((aligned(4096)));
 
 void page_fault(registers_t regs) {
   uint32_t faulting_address;
@@ -25,26 +27,57 @@ void page_fault(registers_t regs) {
   kprintf("PAGE FAULT\n");
 }
 
-void enable_paging(uint32_t *dir) {
+void load_directory(uint32_t *dir) {
   __asm__ volatile("mov %0, %%cr3":: "r"(dir));
+}
+
+void enable_paging() {
   uint32_t cr0;
   __asm__ volatile("mov %%cr0, %0": "=r"(cr0));
   cr0 |= 0x80000001; // Enable paging!
   __asm__ volatile("mov %0, %%cr0":: "r"(cr0));
 }
 
+page_addr_t kalloc_frame() {
+  uint32_t bitmap_index;
+  uint32_t element_index;
+  uint32_t page_frame_number;
+  
+  for (bitmap_index = 0; bitmap_index < NPAGES/ENTRY_WIDTH; bitmap_index++)
+    if (bitmap[bitmap_index] != 0) break; // FIXME
+
+  if (bitmap_index >= NPAGES/ENTRY_WIDTH)
+    return -1;
+
+  for (element_index = 0; element_index < ENTRY_WIDTH; element_index++)
+    if ((bitmap[bitmap_index] & (1U << element_index)) != 0) break; // FIXME
+
+  if ((bitmap[bitmap_index] & (1U << element_index)) == 0)
+    return -1;
+
+  bitmap[bitmap_index] &= ~(1U << element_index);
+
+  page_frame_number = bitmap_index * ENTRY_WIDTH + element_index;
+  return page_frame_number * PAGE_SIZE;
+}
+
 void paging_init() {
-  int i;
+  unsigned int i;
   for(i = 0; i < 1024; i++) {
-    page_directory[i] = 0x00000002;
+    page_dir[i] = 0x00000002;
+  }
+  
+  for(i = 0; i < NPAGES/ENTRY_WIDTH; i++) {
+    bitmap[i] = ~0;
   }
 
   for(i = 0; i < 1024; i++) {
-    first_page_table[i] = (i * 0x1000) | 3; // attributes: supervisor level, read/write, present.
+    page_table[i] = (i * 0x1000) | 3;
   }
-  
-  page_directory[0] = ((unsigned int)first_page_table) | 3;
+
+  page_dir[0] = ((unsigned int)page_table) | 3;
   
   register_interrupt_handler(14, &page_fault);
-  enable_paging(page_directory);
+  load_directory(page_dir);
+  enable_paging();
 }