Create pmm.c

Add implementation for the physical memory manager pmm

kernel/pmm.h

@@ -0,0 +1,21 @@
+#ifndef PMM_H
+#define PMM_H
+
+#include <stdint.h>
+#include <stddef.h>
+#include "memmap.h"
+#include "paging.h" // For PAGE_SIZE
+
+#define BLOCKS_PER_BYTE 8
+
+void pmm_init(memory_map_entry_t* mmap, uint32_t mmap_size, uintptr_t bitmap_addr);
+void pmm_mark_used(uintptr_t addr);
+void pmm_mark_free(uintptr_t addr);
+
+void* pmm_alloc_block();
+void  pmm_free_block(void* addr);
+
+uint32_t pmm_get_used_block_count();
+uint32_t pmm_get_free_block_count();
+
+#endif

pmm.c

@@ -0,0 +1,102 @@
+#include "pmm.h"
+#include "memory.h" // For memset
+
+static uint32_t* pmm_bitmap = NULL;
+static uint32_t  max_blocks = 0;
+static uint32_t  used_blocks = 0;
+
+// Internal bitmap helpers
+static inline void bitmap_set(uint32_t bit) {
+    pmm_bitmap[bit / 32] |= (1 << (bit % 32));
+}
+
+static inline void bitmap_unset(uint32_t bit) {
+    pmm_bitmap[bit / 32] &= ~(1 << (bit % 32));
+}
+
+static inline int bitmap_test(uint32_t bit) {
+    return pmm_bitmap[bit / 32] & (1 << (bit % 32));
+}
+
+void pmm_init(memory_map_entry_t* mmap, uint32_t mmap_size, uintptr_t bitmap_addr) {
+    // 1. Calculate total memory from mmap to find max_blocks
+    uint64_t total_mem = 0;
+    for (uint32_t i = 0; i < mmap_size; i++) {
+        if (mmap[i].type == 1) { // Available RAM
+            total_mem = mmap[i].base_addr + mmap[i].length;
+        }
+    }
+
+    max_blocks = (uint32_t)(total_mem / PAGE_SIZE);
+    used_blocks = max_blocks; 
+    pmm_bitmap = (uint32_t*)bitmap_addr;
+
+    // 2. Default all memory to "Reserved" (1s)
+    memset(pmm_bitmap, 0xFF, max_blocks / BLOCKS_PER_BYTE);
+
+    // 3. Mark only the regions reported as Type 1 (Available) as free (0s)
+    for (uint32_t i = 0; i < mmap_size; i++) {
+        if (mmap[i].type == 1) {
+            uint32_t start_block = (uint32_t)(mmap[i].base_addr / PAGE_SIZE);
+            uint32_t block_count = (uint32_t)(mmap[i].length / PAGE_SIZE);
+            
+            for (uint32_t j = 0; j < block_count; j++) {
+                bitmap_unset(start_block + j);
+                used_blocks--;
+            }
+        }
+    }
+
+    // 4. Critical: Re-protect the first 1MB (BIOS/VGA/Real Mode stuff)
+    for (uint32_t i = 0; i < (1024 * 1024) / PAGE_SIZE; i++) {
+        pmm_mark_used(i * PAGE_SIZE);
+    }
+
+    // 5. Critical: Re-protect the Kernel + Page Tables
+    // Since your paging tables are at 0x200000 and linker at 1MB, 
+    // mark everything from 0x100000 to roughly 0x400000 as used for safety.
+    for (uint32_t i = 0x100000 / PAGE_SIZE; i < 0x400000 / PAGE_SIZE; i++) {
+        pmm_mark_used(i * PAGE_SIZE);
+    }
+    
+    // 6. Protect the bitmap itself
+    uint32_t bitmap_size_blocks = (max_blocks / BLOCKS_PER_BYTE) / PAGE_SIZE + 1;
+    for(uint32_t i = 0; i < bitmap_size_blocks; i++) {
+        pmm_mark_used(bitmap_addr + (i * PAGE_SIZE));
+    }
+}
+
+void pmm_mark_used(uintptr_t addr) {
+    uint32_t block = addr / PAGE_SIZE;
+    if (!bitmap_test(block)) {
+        bitmap_set(block);
+        used_blocks++;
+    }
+}
+
+void pmm_mark_free(uintptr_t addr) {
+    uint32_t block = addr / PAGE_SIZE;
+    if (bitmap_test(block)) {
+        bitmap_unset(block);
+        used_blocks--;
+    }
+}
+
+void* pmm_alloc_block() {
+    for (uint32_t i = 0; i < max_blocks / 32; i++) {
+        if (pmm_bitmap[i] != 0xFFFFFFFF) {
+            for (int j = 0; j < 32; j++) {
+                if (!bitmap_test(i * 32 + j)) {
+                    uint32_t addr = (i * 32 + j) * PAGE_SIZE;
+                    pmm_mark_used(addr);
+                    return (void*)addr;
+                }
+            }
+        }
+    }
+    return NULL; // OOM
+}
+
+void pmm_free_block(void* addr) {
+    pmm_mark_free((uintptr_t)addr);
+}