Small kernel heap for VMM internals, kmalloc/kfree

src/mem/heap/kheap.c

@@ -0,0 +1,106 @@
+#include "kheap.h"
+#include "mem/paging/paging.h"
+#include "mem/paging/pmm.h"
+#include <stddef.h>
+#include <kernel.h>
+
+extern uint64_t kernel_phys_base;
+extern uint64_t kernel_virt_base;
+
+uintptr_t kheap_start;
+
+static struct heap_block_t* head = NULL;
+static uintptr_t end;
+
+// Kernel root table (level 4)
+extern uint64_t *kernel_pml4;
+
+static void kheap_map_page()
+{
+    uintptr_t phys = pmm_alloc();
+    paging_map_page(kernel_pml4, end, phys, PTE_PRESENT | PTE_WRITABLE | PTE_NOEXEC);
+    end += PAGE_SIZE;
+    DEBUG("Mapped first kheap page");
+}
+
+void kheap_init()
+{
+    kheap_start = ALIGN_UP(kernel_virt_base + KERNEL_SIZE, PAGE_SIZE);
+    end = kheap_start;
+
+    // At least 1 page must be mapped for it to work
+    kheap_map_page();
+
+    // Give linked list head its properties
+    head = (struct heap_block_t*)kheap_start;
+    head->size = PAGE_SIZE - sizeof(struct heap_block_t);
+    head->free = true;
+    head->next = NULL;
+    DEBUG("kheap initialized, head=0x%p, size=%u", head, head->size);
+}
+
+void* kmalloc(size_t size)
+{
+    // No size, no memory allocated!
+    if (!size) return NULL;
+
+    struct heap_block_t* curr = head;
+
+    while (curr)
+    {
+        // Is block free and big enough for us?
+        if (curr->free && curr->size >= size)
+        {
+            // We split the block if it is big enough
+            if (curr->size > size + sizeof(struct heap_block_t))
+            {
+                struct heap_block_t* new_block = (struct heap_block_t*)((uintptr_t)curr + sizeof(struct heap_block_t) + size);
+                // We have to subtract the size of our block struct
+                new_block->size = curr->size - size - sizeof(struct heap_block_t);
+                new_block->free = true;
+
+                // Then we chain up the block in the list
+                new_block->next = curr->next;
+                curr->next = new_block;
+
+                curr->size = size;
+            }
+
+            // Found a good block, we return it
+            curr->free = false;
+            return (void*)((uintptr_t)curr + sizeof(struct heap_block_t));
+        }
+        // Continue browsing the list if nothing good was found yet
+        curr = curr->next;
+    }
+
+    // If we're hear it means we didn't have enough memory
+    // for the block allocation. So we will allocate more..
+    uintptr_t old_end = end;
+    kheap_map_page();
+
+    struct heap_block_t* block = (struct heap_block_t*)old_end;
+    block->size = PAGE_SIZE - sizeof(struct heap_block_t);
+    block->free = false;
+    block->next = NULL;
+
+    // Put the block at the end of the list
+    curr = head;
+    while (curr->next)
+    {
+        curr = curr->next;
+    }
+    curr->next = block;
+
+    return (void*)((uintptr_t)block + sizeof(struct heap_block_t));
+}
+
+void kfree(void* ptr)
+{
+    // Nothing to free
+    if (!ptr) return;
+
+    // Set it free!
+    struct heap_block_t* block = (struct heap_block_t*)((uintptr_t)ptr - sizeof(struct heap_block_t));
+    block->free = true;
+}