feat/kernel: Added First-Fit algorithm for kernel heap

kernel/src/boot/emk.h

@@ -4,12 +4,14 @@
 
 #include <boot/limine.h>
 #include <stdint.h>
+#include <mm/vmm.h>
 
 extern uint64_t hhdm_offset;
 extern struct limine_memmap_response *memmap;
 extern uint64_t kvirt;
 extern uint64_t kphys;
 extern uint64_t kstack_top;
+extern vctx_t *kvm_ctx;
 
 #define HIGHER_HALF(ptr) ((void *)((uint64_t)(ptr) < hhdm_offset ? (uint64_t)(ptr) + hhdm_offset : (uint64_t)(ptr)))
 #define PHYSICAL(ptr) ((void *)((uint64_t)(ptr) >= hhdm_offset ? (uint64_t)(ptr) - hhdm_offset : (uint64_t)(ptr)))

kernel/src/emk.c

@@ -12,6 +12,7 @@
 #include <mm/pmm.h>
 #include <arch/paging.h>
 #include <mm/vmm.h>
+#include <mm/heap.h>
 
 __attribute__((used, section(".limine_requests"))) static volatile LIMINE_BASE_REVISION(3);
 __attribute__((used, section(".limine_requests"))) static volatile struct limine_memmap_request memmap_request = {
@@ -31,6 +32,7 @@ struct limine_memmap_response *memmap = NULL;
 uint64_t kvirt = 0;
 uint64_t kphys = 0;
 uint64_t kstack_top = 0;
+vctx_t *kvm_ctx = NULL;
 
 void emk_entry(void)
 {
@@ -91,7 +93,7 @@ void emk_entry(void)
     log_early("Initialized paging");
 
     /* Kernel Virtual Memory Context, not to be confused with KVM */
-    vctx_t *kvm_ctx = vinit(kernel_pagemap, 0x1000);
+    kvm_ctx = vinit(kernel_pagemap, 0x1000);
     if (!kvm_ctx)
     {
         kpanic(NULL, "Failed to create kernel VMM context");
@@ -108,5 +110,18 @@ void emk_entry(void)
     vfree(kvm_ctx, b);
     log_early("Initialized virtual page manager");
 
+    /* Setup kernel heap */
+    heap_init();
+    char *c = kmalloc(1);
+    if (!c)
+    {
+        kpanic(NULL, "Failed to allocate single byte on heap");
+    }
+
+    *c = 32;
+    log_early("Allocated 1 byte @ %llx", (uint64_t)c);
+    kfree(c);
+    log_early("Initialized kernel heap");
+
     hlt();
 }

kernel/src/mm/heap.h

@@ -0,0 +1,11 @@
+/* EMK 1.0 Copyright (c) 2025 Piraterna */
+#ifndef HEAP_H
+#define HEAP_H
+
+#include <stddef.h>
+
+void heap_init();
+void *kmalloc(size_t size);
+void kfree(void *ptr);
+
+#endif // HEAP_H

kernel/src/mm/heap/ff.c

@@ -0,0 +1,82 @@
+/* EMK 1.0 Copyright (c) 2025 Piraterna */
+#include <mm/heap/ff.h>
+#include <mm/heap.h>
+#include <mm/vmm.h>
+#include <mm/pmm.h>
+#include <boot/emk.h>
+#include <util/align.h>
+#include <sys/kpanic.h>
+
+void *pool;
+block_t *freelist = NULL;
+
+void heap_init()
+{
+    pool = valloc(kvm_ctx, FF_POOL_SIZE, VALLOC_RW);
+    if (!pool)
+        kpanic(NULL, "Failed to alloc memory for the heap pool");
+    freelist = (block_t *)pool;
+    freelist->size = (FF_POOL_SIZE * PAGE_SIZE) - sizeof(block_t);
+    freelist->next = NULL;
+}
+
+void *kmalloc(size_t size)
+{
+    if (size == 0)
+        return NULL;
+
+    size = ALIGN_UP(size, 8);
+
+    block_t *prev = NULL;
+    block_t *cur = freelist;
+
+    while (cur)
+    {
+        if (cur->size >= size)
+        {
+            size_t tot_size = sizeof(block_t) + size;
+
+            if (cur->size >= ALIGN_UP(tot_size + sizeof(block_t), 8))
+            {
+                /* do splitting */
+                block_t *new_block = (block_t *)((uint8_t *)cur + tot_size);
+                new_block->size = cur->size - tot_size;
+                new_block->next = cur->next;
+
+                cur->size = size;
+
+                if (prev)
+                    prev->next = new_block;
+                else
+                    freelist = new_block;
+            }
+            else
+            {
+                /* use entire block */
+                if (prev)
+                    prev->next = cur->next;
+                else
+                    freelist = cur->next;
+            }
+
+            return (void *)((uint8_t *)cur + sizeof(block_t));
+        }
+        prev = cur;
+        cur = cur->next;
+    }
+
+    return NULL;
+}
+
+void kfree(void *ptr)
+{
+    if (!ptr)
+        return;
+
+    /* get block header */
+    block_t *block = (block_t *)((uint8_t *)ptr - sizeof(block_t));
+
+    /* insert freed block at head of freelist */
+    block->next = freelist;
+    freelist = block;
+}

kernel/src/mm/heap/ff.h

@@ -0,0 +1,18 @@
+/* EMK 1.0 Copyright (c) 2025 Piraterna */
+#ifndef FF_H
+#define FF_H
+
+/* Kevin's simple First-Fit allocator */
+
+#include <stdint.h>
+#include <stddef.h>
+
+#define FF_POOL_SIZE 512 // 2MB, in pages
+
+typedef struct block
+{
+    size_t size;
+    struct block *next;
+} block_t;
+
+#endif // FF_H