...

src/boot/main.c

@@ -1,55 +1,8 @@
 #include "console.h"
-#include "multiboot2.h"
+#include "pmm.h"
-
-#include <def.h>
-#include "console.h"
-#include "multiboot2.h"
-#include "panic.h"
-#include "util.h"
-
-#define MAX_REGIONS 64
-
-typedef struct {
-    u64 base_addr;
-    u64 length;
-} memory_region;
-
-extern uptr kernel_start;
-extern uptr kernel_end;
-
-static memory_region memory_regions[MAX_REGIONS] = {0};
-static size_t memory_region_count = 0;
-
-static void find_memory_regions() {
-    multiboot_tag_mmap *tag = multiboot_get_mmap();
-    if (tag == NULL) {
-        boot_panic("Multiboot did not provide mmap tag");
-    }
-
-    u32 entry_count = (tag->size - 16) / tag->entry_size;
-    u8 *entry_ptr = (u8*)tag->entries;
-
-    for (u32 i = 0; i < entry_count; ++i) {
-        multiboot_mmap_entry *entry = (multiboot_mmap_entry*)entry_ptr;
-
-        if (entry->type == MULTIBOOT_MEMORY_AVAILABLE) {
-            if (memory_region_count >= MAX_REGIONS) {
-                boot_panic("Too many memory regions");
-            }
-
-            memory_regions[memory_region_count++] = (memory_region){ entry->base_addr, entry->length };
-        }
-
-        entry_ptr += tag->entry_size;
-    }
-}
 
 // We are now in long mode with kernel pages and vga buffer identity mapped
 void x86_64_main() {
     console_clear();
-    find_memory_regions();
+    pmm_init();
-
-    for (u32 i = 0; i < memory_region_count; ++i) {
-        kprintf("region: base_addr=0x%X, length=0x%X\n", memory_regions[i].base_addr, memory_regions[i].length);
-    }
 }

src/boot/multiboot2.c

@@ -1,4 +1,5 @@
 #include "multiboot2.h"
+#include "symbols.h"
 
 // [size:4][reserved:4][data:N]
 #define INFO_DATA_OFFSET    8
@@ -6,10 +7,8 @@
 #define TAG_TYPE_OFFSET     0
 #define TAG_SIZE_OFFSET     4
 
-extern u8 multiboot_info[];
-
 void *multiboot_get_tag(u32 type) {
-    uptr current = (uptr)&multiboot_info + INFO_DATA_OFFSET;
+    uptr current = get_multiboot_info() + INFO_DATA_OFFSET;
 
     while (true) {
         u32 tag_type = *(u32*)(current + TAG_TYPE_OFFSET);
@@ -24,7 +23,7 @@ void *multiboot_get_tag(u32 type) {
         }
 
         // note(nub31): Each tag is aligned to 8 bytes
-        current = align_up(current + tag_size, 8);
+        current = ALIGN_UP(current + tag_size, 8);
     }
 
     return NULL;

src/boot/multiboot2.h

@@ -265,6 +265,10 @@ static inline multiboot_tag_mmap *multiboot_get_mmap() {
     return multiboot_get_tag(MULTIBOOT_TAG_TYPE_MMAP);
 }
 
+static inline size_t get_mmap_entry_count(multiboot_tag_mmap *mmap) {
+    return (mmap->size - 16) / mmap->entry_size;
+}
+
 static inline multiboot_tag_vbe *multiboot_get_vbe() {
     return multiboot_get_tag(MULTIBOOT_TAG_TYPE_VBE);
 }

src/boot/pmm.c

@@ -0,0 +1,116 @@
+#include "pmm.h"
+#include "util.h"
+#include "panic.h"
+#include "multiboot2.h"
+#include "symbols.h"
+#include <def.h>
+
+#define PAGE_SIZE 4096
+#define MAX_PHYS_MEM  GiB(128)
+#define MAX_PAGES (MAX_PHYS_MEM / PAGE_SIZE)
+#define BITMAP_SIZE ((MAX_PAGES + 63) / 64)
+
+static u64 pmm_bitmap[BITMAP_SIZE];
+
+static inline void bitmap_set(size_t bit) {
+    pmm_bitmap[bit / 64] |=  (U64_C(1) << (bit % 64));
+}
+
+static inline void bitmap_clear(size_t bit) {
+    pmm_bitmap[bit / 64] &= ~(U64_C(1) << (bit % 64));
+}
+
+static inline int bitmap_test(size_t bit) {
+    return pmm_bitmap[bit / 64] & (U64_C(1) << (bit % 64));
+}
+
+static inline size_t to_page(uptr addr) {
+    if (addr % PAGE_SIZE != 0) {
+        boot_panic("Address is not page aligned");
+    }
+
+    return addr / PAGE_SIZE;
+}
+
+static inline uptr to_addr(size_t page) {
+    return page * PAGE_SIZE;
+}
+
+static void clear_range(size_t start_page, size_t end_page) {
+    if (start_page >= MAX_PAGES) {
+        return;
+    }
+
+    if (end_page > MAX_PAGES) {
+        end_page = MAX_PAGES;
+    }
+
+    for (size_t j = start_page; j < end_page; ++j) {
+        bitmap_clear(j);
+    }
+}
+
+static void set_range(size_t start_page, size_t end_page) {
+    if (start_page >= MAX_PAGES) {
+        return;
+    }
+
+    if (end_page > MAX_PAGES) {
+        end_page = MAX_PAGES;
+    }
+
+    for (size_t j = start_page; j < end_page; ++j) {
+        bitmap_set(j);
+    }
+}
+
+void pmm_init() {
+    for (size_t i = 0; i < BITMAP_SIZE; i++) {
+        pmm_bitmap[i] = U64_MAX;
+    }
+
+    multiboot_tag_mmap *mmap = multiboot_get_mmap();
+    if (mmap == NULL) {
+        boot_panic("No memory map found");
+    }
+
+    for (size_t i = 0; i < get_mmap_entry_count(mmap); ++i) {
+        multiboot_mmap_entry entry = mmap->entries[i];
+        if (entry.type == MULTIBOOT_MEMORY_AVAILABLE) {
+            size_t start_page = to_page(ALIGN_DOWN(entry.base_addr, PAGE_SIZE));
+            size_t end_page = to_page(ALIGN_UP(entry.base_addr + entry.length, PAGE_SIZE));
+
+            clear_range(start_page, end_page);
+        }
+    }
+
+    size_t start_page = to_page(ALIGN_DOWN(get_kernel_start(), PAGE_SIZE));
+    size_t end_page = to_page(ALIGN_UP(get_kernel_end(), PAGE_SIZE));
+
+    set_range(start_page, end_page);
+}
+
+void *pmm_alloc_page() {
+    for (size_t i = 0; i < MAX_PAGES; ++i) {
+        if (!bitmap_test(i)) {
+            bitmap_set(i);
+            return (void*)to_addr(i);
+        }
+    }
+
+    boot_panic("Out of physical memory");
+}
+
+void pmm_free_page(void *addr) {
+    size_t page = to_page((uptr)addr);
+
+    if (page >= MAX_PAGES) {
+        boot_panic("Trying to free page beyond physical memory limit");
+    }
+
+    if (!bitmap_test(page)) {
+        boot_panic("Page is already free");
+    }
+
+    bitmap_clear(page);
+}

src/boot/pmm.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void pmm_init();

src/boot/symbols.c

@@ -0,0 +1,19 @@
+#include "symbols.h"
+
+extern u8 kernel_start[];
+
+uptr get_kernel_start() {
+    return (uptr)&kernel_start;
+}
+
+extern u8 kernel_end[];
+
+uptr get_kernel_end() {
+    return (uptr)&kernel_end;
+}
+
+extern u8 multiboot_info[];
+
+uptr get_multiboot_info() {
+    return (uptr)&multiboot_info;
+}

src/boot/symbols.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <def.h>
+
+uptr get_kernel_start();
+uptr get_kernel_end();
+uptr get_multiboot_info();

src/boot/util.h

@@ -1,12 +1,9 @@
 #pragma once
 
-static inline uptr align_up(uptr value, size_t alignment) {
+#include <def.h>
-    return (value + alignment - 1) / alignment * alignment;
-}
 
-static inline uptr align_down(uptr value, size_t alignment) {
+#define ALIGN_UP(value, alignment) ((value + alignment - 1) / alignment * alignment)
-    return value - (value % alignment);
+#define ALIGN_DOWN(value, alignment) (value - (value % alignment))
-}
 
 static inline void hlt() {
     asm("hlt");