libc: Add malloc(), calloc(), realloc() and free()

This lets us allocate more than one page of memory from the user side.

apps/app.c

@@ -1,11 +1,9 @@
-#include <bits/mmap-flags.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/syscall.h>
+#include <sys/mman.h>
 #include <time.h>
-#include <unistd.h>
 
 void bye()
 {
@@ -24,17 +22,11 @@ int main()
 
     console_write("\n", 1);
 
-    long rc = syscall(SYS_allocate_memory, 4096, PROT_READ | PROT_WRITE);
-    if (rc < 0)
-    {
-        printf("allocate_memory: %s\n", strerror(-rc));
-        return 1;
-    }
-    char* address = (char*)rc;
+    char* address = (char*)malloc(1);
     printf("address: %p\n", address);
     printf("memory at address: %c\n", *address);
     *address = 'e';
     printf("memory at address: %c\n", *address);
 
-    syscall(SYS_deallocate_memory, address);
+    free(address);
 }

kernel/CMakeLists.txt

@@ -3,11 +3,13 @@
 set(SOURCES 
     src/main.cpp
     src/Log.cpp
+    src/cxxabi.cpp
     src/video/Framebuffer.cpp
     src/video/TextConsole.cpp
     src/memory/MemoryManager.cpp
     src/memory/Heap.cpp
     src/memory/KernelVM.cpp
+    src/memory/UserVM.cpp
     src/memory/MemoryMap.cpp
     src/boot/Init.cpp
     src/arch/Serial.cpp

kernel/src/cxxabi.cpp

@@ -0,0 +1,52 @@
+typedef void* (*cxa_atexit_func_t)(void*);
+
+struct cxa_atexit_entry
+{
+    cxa_atexit_func_t function;
+    void* argument;
+    void* dso_handle;
+};
+
+#define CXA_ATEXIT_MAX 64
+
+int cxa_atexit_entry_count = 0;
+
+cxa_atexit_entry cxa_atexit_entries[CXA_ATEXIT_MAX];
+
+__attribute__((visibility("hidden"))) void* __dso_handle = 0;
+
+extern "C"
+{
+    int __cxa_atexit(cxa_atexit_func_t func, void* arg, void* dso)
+    {
+        if (cxa_atexit_entry_count >= CXA_ATEXIT_MAX) return -1;
+        cxa_atexit_entries[cxa_atexit_entry_count].function = func;
+        cxa_atexit_entries[cxa_atexit_entry_count].argument = arg;
+        cxa_atexit_entries[cxa_atexit_entry_count].dso_handle = dso;
+        cxa_atexit_entry_count++;
+        return 0;
+    }
+
+    void __cxa_finalize(void* f)
+    {
+        int i = cxa_atexit_entry_count;
+        if (!f)
+        {
+            while (i--)
+            {
+                if (cxa_atexit_entries[i].function) { cxa_atexit_entries[i].function(cxa_atexit_entries[i].argument); }
+            }
+        }
+        else
+        {
+            while (i--)
+            {
+                if (cxa_atexit_entries[i].function == (cxa_atexit_func_t)f)
+                {
+                    cxa_atexit_entries[i].function(cxa_atexit_entries[i].argument);
+                    cxa_atexit_entries[i].function = 0;
+                }
+            }
+        }
+    }
+}

kernel/src/memory/Heap.cpp

@@ -1,422 +1,14 @@
 #include "memory/Heap.h"
-#include "Log.h"
 #include "arch/MMU.h"
-#include "arch/Serial.h"
-#include "memory/KernelVM.h"
 #include "memory/MemoryManager.h"
-#include <luna/Alignment.h>
-#include <luna/Alloc.h>
-#include <luna/CString.h>
-#include <luna/LinkedList.h>
-#include <luna/SafeArithmetic.h>
-#include <luna/ScopeGuard.h>
-#include <luna/SystemError.h>
+#include <luna/Heap.h>
 
-namespace std
+Result<void*> allocate_pages_impl(usize count)
 {
-    const nothrow_t nothrow;
+    return (void*)TRY(MemoryManager::alloc_for_kernel(count, MMU::ReadWrite | MMU::NoExecute));
 }
 
-static constexpr int BLOCK_USED = 1 << 0;
-static constexpr int BLOCK_START_MEM = 1 << 1;
-static constexpr int BLOCK_END_MEM = 1 << 2;
-
-static constexpr usize BLOCK_MAGIC = 0x6d616c6c6f63210a; // echo 'malloc!' | hexdump -C (includes a newline)
-static constexpr usize BLOCK_DEAD = 0xdeaddeaddeaddead;
-
-static constexpr u8 KMALLOC_SCRUB_BYTE = 0xac;
-static constexpr u8 KFREE_SCRUB_BYTE = 0xde;
-
-static constexpr usize MINIMUM_PAGES_PER_ALLOCATION = 4;
-
-struct HeapBlock : LinkedListNode<HeapBlock>
+Result<void> release_pages_impl(void* address, usize count)
 {
-    usize req_size;
-    usize full_size;
-    int status;
-    usize magic;
-};
-
-static_assert(sizeof(HeapBlock) == 48UL);
-
-static const isize HEAP_BLOCK_SIZE = 48;
-
-static LinkedList<HeapBlock> heap;
-
-static Result<HeapBlock*> allocate_pages(usize count)
-{
-    void* const ptr = (void*)TRY(MemoryManager::alloc_for_kernel(count, MMU::ReadWrite | MMU::NoExecute));
-    return (HeapBlock*)ptr;
-}
-
-static Result<void> release_pages(void* ptr, usize count)
-{
-    return MemoryManager::unmap_owned_and_free_vm((u64)ptr, count);
-}
-
-// If we're allocating a large amount of memory, map enough pages for it, but otherwise just use the default amount of
-// pages.
-static usize get_pages_for_allocation(usize bytes)
-{
-    usize pages = get_blocks_from_size(bytes, ARCH_PAGE_SIZE);
-    if (pages < MINIMUM_PAGES_PER_ALLOCATION) pages = MINIMUM_PAGES_PER_ALLOCATION;
-    return pages;
-}
-
-static bool is_block_free(HeapBlock* block)
-{
-    return !(block->status & BLOCK_USED);
-}
-
-static usize space_available(HeapBlock* block)
-{
-    expect(!is_block_free(block), "Attempting to split a free block");
-    return block->full_size - block->req_size;
-}
-
-// The heap block is stored right behind a memory block.
-static HeapBlock* get_heap_block_for_pointer(void* ptr)
-{
-    return (HeapBlock*)offset_ptr(ptr, -HEAP_BLOCK_SIZE);
-}
-
-static void* get_pointer_from_heap_block(HeapBlock* block)
-{
-    return (void*)offset_ptr(block, HEAP_BLOCK_SIZE);
-}
-
-static usize get_fair_offset_to_split_at(HeapBlock* block, usize min)
-{
-    usize available = space_available(block);
-
-    available -= min; // reserve at least min size for the new block.
-
-    available -= (available /
-                  2); // reserve half of the rest for the new block, while still leaving another half for the old one.
-
-    available = align_down<16>(available); // Everything has to be aligned on a 16-byte boundary
-
-    return available + block->req_size;
-}
-
-static Option<HeapBlock*> split(HeapBlock* block, usize size)
-{
-    const usize available = space_available(block); // How much space can we steal from this block?
-    const usize old_size =
-        block->full_size; // Save the old value of this variable since we are going to use it after modifying it
-
-    if (available < (size + sizeof(HeapBlock)))
-        return {}; // This block hasn't got enough free space to hold the requested size.
-
-    const usize offset = get_fair_offset_to_split_at(block, size + sizeof(HeapBlock));
-    block->full_size = offset; // shrink the old block to fit this offset
-
-    HeapBlock* new_block = offset_ptr(block, offset + sizeof(HeapBlock));
-
-    new_block->magic = BLOCK_MAGIC;
-    new_block->status = (block->status & BLOCK_END_MEM) ? BLOCK_END_MEM : 0;
-    new_block->full_size = old_size - (offset + sizeof(HeapBlock));
-    heap.add_after(block, new_block);
-
-    block->status &= ~BLOCK_END_MEM; // this block is no longer the last block in its memory range
-
-    return new_block;
-}
-
-static Result<void> combine_forward(HeapBlock* block)
-{
-    // This block ends a memory range, cannot be combined with blocks outside its range.
-    if (block->status & BLOCK_END_MEM) return {};
-
-    // The caller needs to ensure there is a next block.
-    HeapBlock* const next = heap.next(block).value();
-    // This block starts a memory range, cannot be combined with blocks outside its range.
-    if (next->status & BLOCK_START_MEM) return {};
-
-    heap.remove(next);
-    next->magic = BLOCK_DEAD;
-
-    if (next->status & BLOCK_END_MEM)
-    {
-        if (next->status & BLOCK_START_MEM)
-        {
-            const usize pages = get_blocks_from_size(next->full_size + sizeof(HeapBlock), ARCH_PAGE_SIZE);
-            TRY(release_pages(next, pages));
-            return {};
-        }
-        else
-            block->status |= BLOCK_END_MEM;
-    }
-
-    block->full_size += next->full_size + sizeof(HeapBlock);
-
-    return {};
-}
-
-static Result<HeapBlock*> combine_backward(HeapBlock* block)
-{
-    // This block starts a memory range, cannot be combined with blocks outside its range.
-    if (block->status & BLOCK_START_MEM) return block;
-
-    // The caller needs to ensure there is a last block.
-    HeapBlock* const last = heap.previous(block).value();
-    // This block ends a memory range, cannot be combined with blocks outside its range.
-    if (last->status & BLOCK_END_MEM) return block;
-    heap.remove(block);
-    block->magic = BLOCK_DEAD;
-
-    if (block->status & BLOCK_END_MEM)
-    {
-        if (block->status & BLOCK_START_MEM)
-        {
-            const usize pages = get_blocks_from_size(block->full_size + sizeof(HeapBlock), ARCH_PAGE_SIZE);
-            TRY(release_pages(block, pages));
-            return last;
-        }
-        else
-            last->status |= BLOCK_END_MEM;
-    }
-
-    last->full_size += block->full_size + sizeof(HeapBlock);
-
-    return last;
-}
-
-Result<void*> kmalloc(usize size, bool should_scrub)
-{
-    if (!size) return (void*)BLOCK_MAGIC;
-
-    size = align_up<16>(size);
-
-    if (heap.count() == 0)
-    {
-        const usize pages = get_pages_for_allocation(size + sizeof(HeapBlock));
-        HeapBlock* const block = TRY(allocate_pages(pages));
-
-        block->full_size = (pages * ARCH_PAGE_SIZE) - sizeof(HeapBlock);
-        block->magic = BLOCK_MAGIC;
-        block->status = BLOCK_START_MEM | BLOCK_END_MEM;
-        heap.append(block);
-    }
-
-    Option<HeapBlock*> block = heap.first();
-    while (block.has_value())
-    {
-        HeapBlock* const current = block.value();
-        // Trying to find a free block...
-        if (is_block_free(current))
-        {
-            if (current->full_size < size)
-            {
-                block = heap.next(current);
-                continue;
-            }
-            break; // We found a free block that's big enough!!
-        }
-        auto rc = split(current, size);
-        if (rc.has_value())
-        {
-            block = rc.value(); // We managed to get a free block from a larger used block!!
-            break;
-        }
-        block = heap.next(current);
-    }
-
-    if (!block.has_value()) // No free blocks, let's allocate a new one
-    {
-        usize pages = get_pages_for_allocation(size + sizeof(HeapBlock));
-        HeapBlock* const current = TRY(allocate_pages(pages));
-
-        current->full_size = (pages * ARCH_PAGE_SIZE) - sizeof(HeapBlock);
-        current->magic = BLOCK_MAGIC;
-        current->status = BLOCK_START_MEM | BLOCK_END_MEM;
-        heap.append(current);
-
-        block = current;
-    }
-
-    HeapBlock* const current = block.value();
-
-    current->req_size = size;
-    current->status |= BLOCK_USED;
-
-    if (should_scrub) { memset(get_pointer_from_heap_block(current), KMALLOC_SCRUB_BYTE, size); }
-
-    return get_pointer_from_heap_block(current);
-}
-
-Result<void> kfree(void* ptr)
-{
-    if (ptr == (void*)BLOCK_MAGIC) return {}; // This pointer was returned from a call to malloc(0)
-    if (!ptr) return {};
-
-    HeapBlock* block = get_heap_block_for_pointer(ptr);
-
-    if (block->magic != BLOCK_MAGIC)
-    {
-        if (block->magic == BLOCK_DEAD)
-        {
-            kerrorln("ERROR: Attempt to free memory at %p, which was already freed", ptr);
-        }
-        else
-            kerrorln("ERROR: Attempt to free memory at %p, which wasn't allocated with kmalloc", ptr);
-
-        return err(EFAULT);
-    }
-
-    if (is_block_free(block))
-    {
-        kerrorln("ERROR: Attempt to free memory at %p, which was already freed", ptr);
-        return err(EFAULT);
-    }
-    else
-        block->status &= ~BLOCK_USED;
-
-    memset(ptr, KFREE_SCRUB_BYTE, block->req_size);
-
-    auto maybe_next = heap.next(block);
-    if (maybe_next.has_value() && is_block_free(maybe_next.value()))
-    {
-        // The next block is also free, thus we can merge!
-        TRY(combine_forward(block));
-    }
-
-    auto maybe_last = heap.previous(block);
-    if (maybe_last.has_value() && is_block_free(maybe_last.value()))
-    {
-        // The last block is also free, thus we can merge!
-        block = TRY(combine_backward(block));
-    }
-
-    if ((block->status & BLOCK_START_MEM) && (block->status & BLOCK_END_MEM))
-    {
-        heap.remove(block);
-        const usize pages = get_blocks_from_size(block->full_size + sizeof(HeapBlock), ARCH_PAGE_SIZE);
-        TRY(release_pages(block, pages));
-    }
-
-    return {};
-}
-
-Result<void*> krealloc(void* ptr, usize size)
-{
-    if (!ptr) return kmalloc(size);
-    if (ptr == (void*)BLOCK_MAGIC) return kmalloc(size);
-    if (!size)
-    {
-        TRY(kfree(ptr));
-        return (void*)BLOCK_MAGIC;
-    }
-
-    HeapBlock* const block = get_heap_block_for_pointer(ptr);
-
-    if (block->magic != BLOCK_MAGIC)
-    {
-        if (block->magic == BLOCK_DEAD)
-        {
-            kerrorln("ERROR: Attempt to realloc memory at %p, which was already freed", ptr);
-        }
-        else
-            kerrorln("ERROR: Attempt to realloc memory at %p, which wasn't allocated with kmalloc", ptr);
-
-        return err(EFAULT);
-    }
-
-    size = align_up<16>(size);
-
-    if (is_block_free(block))
-    {
-        kerrorln("ERROR: Attempt to realloc memory at %p, which was already freed", ptr);
-        return err(EFAULT);
-    }
-
-    if (block->full_size >= size)
-    {
-        // This block is already large enough!
-        // FIXME: Scrub this if necessary.
-        block->req_size = size;
-        return ptr;
-    }
-
-    usize old_size = block->req_size;
-
-    void* const new_ptr = TRY(kmalloc(size, false));
-    memcpy(new_ptr, ptr, old_size > size ? size : old_size);
-    TRY(kfree(ptr));
-
-    if (old_size < size) { memset(offset_ptr(new_ptr, old_size), KMALLOC_SCRUB_BYTE, size - old_size); }
-
-    return new_ptr;
-}
-
-Result<void*> kcalloc(usize nmemb, usize size)
-{
-    const usize realsize = TRY(safe_mul(nmemb, size));
-    void* const ptr = TRY(kmalloc(realsize, false));
-    return memset(ptr, 0, realsize);
-}
-
-void dump_heap_usage()
-{
-    kdbgln("-- Dumping usage stats for kernel heap:");
-    if (!heap.count())
-    {
-        kdbgln("- Heap is not currently being used");
-        return;
-    }
-    usize alloc_total = 0;
-    usize alloc_used = 0;
-    auto block = heap.first();
-    while (block.has_value())
-    {
-        HeapBlock* current = block.value();
-        if (is_block_free(current))
-        {
-            kdbgln("- Available block (%p), of size %zu (%s%s)", (void*)current, current->full_size,
-                   current->status & BLOCK_START_MEM ? "b" : "-", current->status & BLOCK_END_MEM ? "e" : "-");
-            alloc_total += current->full_size + sizeof(HeapBlock);
-        }
-        else
-        {
-            kdbgln("- Used block (%p), of size %zu, of which %zu bytes are being used (%s%s)", (void*)current,
-                   current->full_size, current->req_size, current->status & BLOCK_START_MEM ? "b" : "-",
-                   current->status & BLOCK_END_MEM ? "e" : "-");
-            alloc_total += current->full_size + sizeof(HeapBlock);
-            alloc_used += current->req_size;
-        }
-        block = heap.next(current);
-    }
-
-    kdbgln("-- Total memory allocated for heap: %zu bytes", alloc_total);
-    kdbgln("-- Heap memory in use by the kernel: %zu bytes", alloc_used);
-}
-
-void* operator new(usize size, const std::nothrow_t&) noexcept
-{
-    return kmalloc(size).value_or(nullptr);
-}
-
-void* operator new[](usize size, const std::nothrow_t&) noexcept
-{
-    return kmalloc(size).value_or(nullptr);
-}
-
-void operator delete(void* p) noexcept
-{
-    kfree(p);
-}
-
-void operator delete[](void* p) noexcept
-{
-    kfree(p);
-}
-
-void operator delete(void* p, usize) noexcept
-{
-    kfree(p);
-}
-
-void operator delete[](void* p, usize) noexcept
-{
-    kfree(p);
+    return MemoryManager::unmap_owned_and_free_vm((u64)address, count);
 }

kernel/src/memory/Heap.h

@@ -1,10 +1,7 @@
 #pragma once
-#include <luna/PlacementNew.h>
-#include <luna/Result.h>
+#include <luna/Heap.h>
 
-Result<void*> kmalloc(usize size, bool should_scrub = true);
-Result<void*> kcalloc(usize nmemb, usize size);
-Result<void*> krealloc(void* ptr, usize size);
-Result<void> kfree(void* ptr);
-
-void dump_heap_usage();
+#define kmalloc malloc_impl
+#define kcalloc calloc_impl
+#define krealloc realloc_impl
+#define kfree free_impl

kernel/src/memory/UserVM.cpp

@@ -0,0 +1,115 @@
+#include "memory/UserVM.h"
+#include "Log.h"
+#include "arch/MMU.h"
+#include "memory/Heap.h"
+#include <luna/ScopeGuard.h>
+
+static constexpr u64 VM_BASE = 0x10000000;
+
+static constexpr usize INITIAL_VM_SIZE = 80;
+static constexpr usize MAX_VM_SIZE = 1024 * 1024 * 16;
+
+Result<OwnedPtr<UserVM>> UserVM::try_create()
+{
+    void* const base = TRY(kmalloc(INITIAL_VM_SIZE));
+
+    auto guard = make_scope_guard([&] { kfree(base); });
+
+    OwnedPtr<UserVM> ptr = TRY(make_owned<UserVM>(base, INITIAL_VM_SIZE));
+
+    guard.deactivate();
+
+    return move(ptr);
+}
+
+UserVM::UserVM(void* base, usize size)
+{
+    kdbgln("user vm created with base=%p, size=%zu", base, size);
+    m_bitmap.initialize(base, size);
+    m_bitmap.clear(false);
+}
+
+Result<bool> UserVM::try_expand(usize size)
+{
+    if (m_bitmap.size_in_bytes() == MAX_VM_SIZE) { return false; }
+
+    usize new_size = m_bitmap.size_in_bytes() + size;
+
+    if (new_size > MAX_VM_SIZE) new_size = MAX_VM_SIZE;
+
+    usize old_size = m_bitmap.size_in_bytes();
+
+    void* const base = TRY(krealloc(m_bitmap.location(), new_size));
+
+    m_bitmap.initialize(base, new_size);
+    m_bitmap.clear_region(old_size * 8, (new_size - old_size) * 8, false);
+
+    kdbgln("user vm expanded to base=%p, size=%zu", base, new_size);
+
+    return true;
+}
+
+Result<u64> UserVM::alloc_one_page()
+{
+    u64 index;
+    const auto maybe_index = m_bitmap.find_and_toggle(false);
+    if (!maybe_index.has_value())
+    {
+        bool success = TRY(try_expand());
+        if (!success) return err(ENOMEM);
+        index = TRY(Result<u64>::from_option(m_bitmap.find_and_toggle(false), ENOMEM));
+    }
+    else
+        index = maybe_index.value();
+
+    return VM_BASE + index * ARCH_PAGE_SIZE;
+}
+
+Result<u64> UserVM::alloc_several_pages(usize count)
+{
+    u64 index;
+    const auto maybe_index = m_bitmap.find_and_toggle_region(false, count);
+    if (!maybe_index.has_value())
+    {
+        bool success = TRY(try_expand((count / 8) + INITIAL_VM_SIZE));
+        if (!success) return err(ENOMEM);
+        index = TRY(Result<u64>::from_option(m_bitmap.find_and_toggle_region(false, count), ENOMEM));
+    }
+    else
+        index = maybe_index.value();
+
+    return VM_BASE + index * ARCH_PAGE_SIZE;
+}
+
+Result<void> UserVM::free_one_page(u64 address)
+{
+    if (address < VM_BASE) return err(EINVAL);
+    const u64 index = (address - VM_BASE) / ARCH_PAGE_SIZE;
+    if (index > (MAX_VM_SIZE * 8)) return err(EINVAL);
+
+    if (!m_bitmap.get(index)) return err(EFAULT);
+
+    m_bitmap.set(index, false);
+
+    return {};
+}
+
+Result<void> UserVM::free_several_pages(u64 address, usize count)
+{
+    if (address < VM_BASE) return err(EINVAL);
+    const u64 index = (address - VM_BASE) / ARCH_PAGE_SIZE;
+    if ((index + count) > (MAX_VM_SIZE * 8)) return err(EINVAL);
+
+    // FIXME: Is it necessary to check all pages?
+    if (!m_bitmap.get(index)) return err(EFAULT);
+
+    m_bitmap.clear_region(index, count, false);
+
+    return {};
+}
+
+UserVM::~UserVM()
+{
+    kdbgln("user vm destroyed: base=%p, size=%zu", m_bitmap.location(), m_bitmap.size_in_bytes());
+    kfree(m_bitmap.location());
+}

kernel/src/memory/UserVM.h

@@ -0,0 +1,23 @@
+#pragma once
+#include <luna/Bitmap.h>
+#include <luna/OwnedPtr.h>
+#include <luna/Result.h>
+
+class UserVM
+{
+  public:
+    UserVM(void* base, usize size);
+    ~UserVM();
+
+    Result<u64> alloc_one_page();
+    Result<u64> alloc_several_pages(usize count);
+
+    Result<void> free_one_page(u64 address);
+    Result<void> free_several_pages(u64 address, usize count);
+
+    static Result<OwnedPtr<UserVM>> try_create();
+
+  private:
+    Result<bool> try_expand(usize size = 160);
+    Bitmap m_bitmap;
+};

kernel/src/sys/allocate_memory.cpp

@@ -13,48 +13,41 @@ Result<u64> sys_allocate_memory(Registers*, SyscallArgs args)
     usize size = (usize)args[0];
     int flags = (int)args[1];
 
-    if (size != ARCH_PAGE_SIZE) return err(EINVAL);
     if (flags < 0) return err(EINVAL);
-
     if (size == 0) return 0;
 
+    size = align_up<ARCH_PAGE_SIZE>(size);
+
     Thread* current = Scheduler::current();
-    if (!current->heap_bitmap.initialized())
-    {
-        void* bitmap_location = (void*)TRY(MemoryManager::alloc_for_kernel(1, MMU::ReadWrite));
-        current->heap_bitmap.initialize(bitmap_location, ARCH_PAGE_SIZE);
-        current->heap_bitmap.clear(false);
-    }
 
-    u64 index = TRY(Result<u64>::from_option(current->heap_bitmap.find_and_toggle(false), ENOMEM));
-
-    u64 address = USERSPACE_HEAP_BASE + (index * ARCH_PAGE_SIZE);
+    u64 address = TRY(current->vm_allocator->alloc_several_pages(size / ARCH_PAGE_SIZE));
 
     int mmu_flags = MMU::User | MMU::NoExecute;
     if (flags & PROT_WRITE) mmu_flags |= MMU::ReadWrite;
     if (flags & PROT_EXEC) mmu_flags &= ~MMU::NoExecute;
+    if (flags == PROT_NONE) mmu_flags = MMU::NoExecute;
 
-    kdbgln("allocate_memory: allocating memory at %#lx", address);
+    kdbgln("allocate_memory: allocating memory at %#lx, size=%zu", address, size);
 
-    return MemoryManager::alloc_at(address, 1, mmu_flags);
+    return MemoryManager::alloc_at(address, size / ARCH_PAGE_SIZE, mmu_flags);
 }
 
 Result<u64> sys_deallocate_memory(Registers*, SyscallArgs args)
 {
     u64 address = (u64)args[0];
+    usize size = (usize)args[1];
+
+    if (size == 0) return 0;
+
+    size = align_up<ARCH_PAGE_SIZE>(size);
 
     Thread* current = Scheduler::current();
-    if (!current->heap_bitmap.initialized()) return err(EFAULT);
 
-    u64 index = (address - USERSPACE_HEAP_BASE) / ARCH_PAGE_SIZE;
+    TRY(current->vm_allocator->free_several_pages(address, size / ARCH_PAGE_SIZE));
 
-    if (!current->heap_bitmap.get(index)) return err(EFAULT);
+    kdbgln("deallocate_memory: deallocating memory at %#lx, size=%zu", address, size);
 
-    current->heap_bitmap.set(index, false);
-
-    kdbgln("deallocate_memory: deallocating memory at %#lx", address);
-
-    TRY(MemoryManager::unmap_owned(address, 1));
+    TRY(MemoryManager::unmap_owned(address, size / ARCH_PAGE_SIZE));
 
     return { 0 };
 }

kernel/src/thread/Scheduler.cpp

@@ -126,6 +126,8 @@ namespace Scheduler
 
         auto guard = make_scope_guard([&] { delete thread; });
 
+        thread->vm_allocator = TRY(UserVM::try_create());
+
         PageDirectory* const directory = TRY(MMU::create_page_directory_for_userspace());
 
         auto directory_guard = make_scope_guard([&] {
@@ -178,11 +180,6 @@ namespace Scheduler
 
         if (!thread->is_kernel) MMU::delete_userspace_page_directory(thread->directory);
 
-        if (thread->heap_bitmap.initialized())
-            MemoryManager::unmap_owned_and_free_vm(
-                (u64)thread->heap_bitmap.location(),
-                get_blocks_from_size(thread->heap_bitmap.size_in_bytes(), ARCH_PAGE_SIZE));
-
         delete thread;
     }
 

kernel/src/thread/Thread.h

@@ -1,8 +1,9 @@
 #pragma once
 
 #include "arch/MMU.h"
-#include <luna/Bitmap.h>
+#include "memory/UserVM.h"
 #include <luna/LinkedList.h>
+#include <luna/OwnedPtr.h>
 #include <luna/Result.h>
 #include <luna/Stack.h>
 
@@ -36,7 +37,7 @@ struct Thread : public LinkedListNode<Thread>
     Stack stack;
     Stack kernel_stack;
 
-    Bitmap heap_bitmap;
+    OwnedPtr<UserVM> vm_allocator;
 
     ThreadState state = ThreadState::Runnable;
 

libc/CMakeLists.txt

@@ -10,6 +10,7 @@ set(SOURCES
     src/atexit.cpp
     src/ctype.cpp
     src/time.cpp
+    src/sys/mman.cpp
 )
 
 if(${ARCH} STREQUAL "x86_64")

libc/include/stdlib.h

@@ -52,9 +52,16 @@ extern "C"
     /* Return the result of dividing two long long integers, including the remainder. */
     lldiv_t lldiv(long long, long long);
 
-    void* malloc(size_t);
-    void* calloc(size_t, size_t);
-    void* realloc(void*, size_t);
+    /* Allocate heap memory. */
+    void* malloc(size_t size);
+
+    /* Allocate zero-initialized heap memory. */
+    void* calloc(size_t nmemb, size_t size);
+
+    /* Resize allocated heap memory. */
+    void* realloc(void* ptr, size_t size);
+
+    /* Free heap memory. */
     void free(void*);
 
     /* Abort the program without performing any normal cleanup. */

libc/include/sys/mman.h

@@ -0,0 +1,23 @@
+#ifndef _LUNA_MMAN_H
+#define _LUNA_MMAN_H
+
+#include <bits/mmap-flags.h>
+#include <sys/types.h>
+
+#define PAGE_SIZE 4096UL
+
+#define MAP_FAILED (void*)-1
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    void* allocate_memory(size_t size, int flags);
+    int deallocate_memory(void* address, size_t size);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

libc/src/stdio.cpp

@@ -71,3 +71,9 @@ extern "C"
         return 0;
     }
 }
+
+void debug_log_impl(const char* format, va_list ap)
+{
+    pure_cstyle_format(
+        format, [](char c, void*) { console_write(&c, 1); }, nullptr, ap);
+}

libc/src/stdlib.cpp

@@ -1,4 +1,7 @@
+#define _LUNA_SYSTEM_ERROR_EXTENSIONS
+#include <errno.h>
 #include <limits.h>
+#include <luna/Heap.h>
 #include <luna/NumberParsing.h>
 #include <luna/Utf8.h>
 #include <stdlib.h>
@@ -118,4 +121,42 @@ extern "C"
 
         return code_points;
     }
+
+    void* malloc(size_t size)
+    {
+        auto rc = malloc_impl(size);
+        if (rc.has_error())
+        {
+            errno = rc.error();
+            return nullptr;
+        }
+        return rc.value();
+    }
+
+    void* calloc(size_t nmemb, size_t size)
+    {
+        auto rc = calloc_impl(nmemb, size);
+        if (rc.has_error())
+        {
+            errno = rc.error();
+            return nullptr;
+        }
+        return rc.value();
+    }
+
+    void* realloc(void* ptr, size_t size)
+    {
+        auto rc = realloc_impl(ptr, size);
+        if (rc.has_error())
+        {
+            errno = rc.error();
+            return nullptr;
+        }
+        return rc.value();
+    }
+
+    void free(void* ptr)
+    {
+        free_impl(ptr);
+    }
 }

libc/src/sys/mman.cpp

@@ -0,0 +1,35 @@
+#define _LUNA_SYSTEM_ERROR_EXTENSIONS
+#include <bits/errno-return.h>
+#include <luna/Heap.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+extern "C"
+{
+    void* allocate_memory(size_t size, int flags)
+    {
+        long rc = syscall(SYS_allocate_memory, size, flags);
+        __errno_return(rc, void*);
+    }
+
+    int deallocate_memory(void* address, size_t size)
+    {
+        long rc = syscall(SYS_deallocate_memory, address, size);
+        __errno_return(rc, int);
+    }
+}
+
+Result<void*> allocate_pages_impl(usize count)
+{
+    long rc = syscall(SYS_allocate_memory, count * PAGE_SIZE, PROT_READ | PROT_WRITE);
+    if (rc < 0) { return err((int)-rc); }
+    return (void*)rc;
+}
+
+Result<void> release_pages_impl(void* address, usize count)
+{
+    long rc = syscall(SYS_deallocate_memory, address, count * PAGE_SIZE);
+    if (rc < 0) { return err((int)-rc); }
+    return {};
+}

luna/CMakeLists.txt

@@ -11,11 +11,11 @@ set(FREESTANDING_SOURCES
     src/SystemError.cpp
     src/Bitmap.cpp
     src/Stack.cpp
-    src/Alloc.cpp
     src/OwnedStringView.cpp
     src/Utf8.cpp
     src/TarStream.cpp
     src/DebugLog.cpp
+    src/Heap.cpp
 )
 
 set(SOURCES
@@ -34,6 +34,7 @@ target_compile_options(luna-freestanding PRIVATE -fno-asynchronous-unwind-tables
 target_compile_options(luna-freestanding PRIVATE -nostdlib -mcmodel=kernel)
 
 target_include_directories(luna-freestanding PUBLIC include/)
+target_include_directories(luna-freestanding PRIVATE ${LUNA_ROOT}/kernel/src)
 set_target_properties(luna-freestanding PROPERTIES CXX_STANDARD 20)
 
 add_library(luna ${SOURCES})

luna/include/luna/Alloc.h

@@ -1,38 +1,19 @@
 #pragma once
+#include <luna/Heap.h>
+#include <luna/PlacementNew.h>
 #include <luna/Result.h>
 
-namespace std
-{
-    struct nothrow_t
-    {
-        explicit nothrow_t() = default;
-    };
-
-    extern const nothrow_t nothrow;
-
-    enum class align_val_t : usize
-    {
-    };
-};
-
-[[nodiscard]] void* raw_malloc(usize);
-void raw_free(void*);
-
-void* operator new(usize size, const std::nothrow_t&) noexcept;
-void* operator new[](usize size, const std::nothrow_t&) noexcept;
-void operator delete(void* ptr, usize size, std::align_val_t alignment) noexcept;
-
 template <typename T, class... Args> [[nodiscard]] Result<T*> make(Args... args)
 {
-    T* const result = new (std::nothrow) T(args...);
-    if (!result) return err(ENOMEM);
+    T* const result = (T*)TRY(malloc_impl(sizeof(T)));
+    new (result) T(args...);
     return result;
 }
 
 template <typename T> [[nodiscard]] Result<T*> make_array(usize count)
 {
-    T* const result = new (std::nothrow) T[count];
-    if (!result) return err(ENOMEM);
+    T* const result = (T*)TRY(calloc_impl(count, sizeof(T)));
+    new (result) T[count];
     return result;
 }
 

luna/include/luna/Bitmap.h

@@ -39,6 +39,10 @@ class Bitmap
 
     Option<usize> find_and_toggle(bool value, usize begin = 0);
 
+    Option<usize> find_region(bool value, usize count, usize begin = 0) const;
+
+    Option<usize> find_and_toggle_region(bool value, usize count, usize begin = 0);
+
     void clear(bool value);
     void clear_region(usize start, usize bits, bool value);
 

luna/include/luna/Heap.h

@@ -0,0 +1,30 @@
+#pragma once
+#include <luna/Result.h>
+
+namespace std
+{
+    struct nothrow_t
+    {
+        explicit nothrow_t() = default;
+    };
+
+    extern const nothrow_t nothrow;
+
+    enum class align_val_t : usize
+    {
+    };
+};
+
+void* operator new(usize size, const std::nothrow_t&) noexcept;
+void* operator new[](usize size, const std::nothrow_t&) noexcept;
+void operator delete(void* ptr, usize size, std::align_val_t alignment) noexcept;
+
+extern Result<void*> allocate_pages_impl(usize count);
+extern Result<void> release_pages_impl(void* address, usize count);
+
+Result<void*> malloc_impl(usize size, bool should_scrub = true);
+Result<void*> calloc_impl(usize nmemb, usize size);
+Result<void*> realloc_impl(void* ptr, usize size);
+Result<void> free_impl(void* ptr);
+
+void dump_heap_usage();

luna/include/luna/OwnedPtr.h

@@ -7,6 +7,11 @@ template <typename T> class SharedPtr;
 template <typename T> class OwnedPtr
 {
   public:
+    OwnedPtr()
+    {
+        m_ptr = nullptr;
+    }
+
     OwnedPtr(T* ptr)
     {
         m_ptr = ptr;
@@ -25,6 +30,20 @@ template <typename T> class OwnedPtr
         other.m_ptr = nullptr;
     }
 
+    OwnedPtr<T>& operator=(const OwnedPtr<T>& other) = delete;
+
+    OwnedPtr<T>& operator=(OwnedPtr<T>&& other)
+    {
+        if (&other == this) return *this;
+
+        if (m_ptr) delete m_ptr;
+
+        m_ptr = other.m_ptr;
+        other.m_ptr = nullptr;
+
+        return *this;
+    }
+
     T* ptr() const
     {
         return m_ptr;

luna/include/luna/SharedPtr.h

@@ -30,6 +30,12 @@ template <typename T> class SharedPtr
     using RefCount = __detail::RefCount;
 
   public:
+    SharedPtr()
+    {
+        m_ptr = nullptr;
+        m_ref_count = nullptr;
+    }
+
     SharedPtr(T* ptr, RefCount* ref_count) : m_ptr(ptr), m_ref_count(ref_count)
     {
     }

luna/include/luna/Utf8.h

@@ -18,7 +18,7 @@ class Utf8StringDecoder
     // The caller must ensure that 'buf' is at least code_points() + a NULL wide.
     Result<void> decode(wchar_t* buf) const;
 
-    Result<void> decode(wchar_t* buf, size_t max) const;
+    Result<void> decode(wchar_t* buf, usize max) const;
 
   private:
     const char* m_str;
@@ -40,7 +40,7 @@ class Utf8StringEncoder
     // The caller must ensure that 'buf' is at least byte_length() + a NULL wide.
     Result<void> encode(char* buf) const;
 
-    Result<void> encode(char* buf, size_t max) const;
+    Result<void> encode(char* buf, usize max) const;
 
   private:
     const wchar_t* m_str;

luna/src/Alloc.cpp

@@ -1,38 +0,0 @@
-#include <luna/Alloc.h>
-
-#ifndef USE_FREESTANDING
-#include <stdlib.h>
-#endif
-
-[[nodiscard]] void* raw_malloc(usize size)
-{
-#ifdef USE_FREESTANDING
-    char* const rc = new (std::nothrow) char[size];
-    return (void*)rc;
-#else
-    // return malloc(size);
-    (void)size;
-    return NULL;
-#endif
-}
-
-void raw_free(void* ptr)
-{
-#ifdef USE_FREESTANDING
-    char* const arr = (char*)ptr;
-    delete[] arr;
-#else
-    // return free(ptr);
-    (void)ptr;
-#endif
-}
-
-void operator delete(void* ptr, usize size, std::align_val_t) noexcept
-{
-#ifdef USE_FREESTANDING
-    operator delete(ptr, size);
-#else
-    (void)ptr;
-    (void)size;
-#endif
-}

luna/src/Bitmap.cpp

@@ -132,3 +132,38 @@ Option<usize> Bitmap::find_and_toggle(bool value, usize begin)
     set(index, !value);
     return index;
 }
+
+Option<usize> Bitmap::find_region(bool value, usize count, usize begin) const
+{
+    // FIXME: Optimize this using bit and byte manipulation.
+    u64 region_bits_found = 0;
+    u64 region_start = 0;
+
+    for (u64 index = begin; index < m_size_in_bytes * 8; index++)
+    {
+        if (get(index) != value)
+        {
+            region_bits_found = 0;
+            continue;
+        }
+
+        if (region_bits_found == 0)
+        {
+            region_start = index;
+            region_bits_found++;
+        }
+        else
+            region_bits_found++;
+
+        if (region_bits_found == count) return region_start;
+    }
+
+    return {};
+}
+
+Option<usize> Bitmap::find_and_toggle_region(bool value, usize count, usize begin)
+{
+    usize index = TRY(find_region(value, count, begin));
+    clear_region(index, count, !value);
+    return index;
+}

luna/src/CString.cpp

@@ -68,7 +68,7 @@ extern "C"
     {
         const usize len = strlen(str);
 
-        char* dest = (char*)raw_malloc(len + 1);
+        char* dest = (char*)malloc_impl(len + 1).value_or(nullptr);
         if (!dest) return nullptr;
 
         memcpy(dest, str, len + 1);

luna/src/Heap.cpp

@@ -0,0 +1,400 @@
+#include <luna/Alignment.h>
+#include <luna/Alloc.h>
+#include <luna/CString.h>
+#include <luna/DebugLog.h>
+#include <luna/Heap.h>
+#include <luna/LinkedList.h>
+#include <luna/SafeArithmetic.h>
+#include <luna/ScopeGuard.h>
+#include <luna/SystemError.h>
+
+#ifdef USE_FREESTANDING
+#include "arch/MMU.h"
+#define PAGE_SIZE ARCH_PAGE_SIZE
+#else
+#include <sys/mman.h>
+#endif
+
+namespace std
+{
+    const nothrow_t nothrow;
+}
+
+static constexpr int BLOCK_USED = 1 << 0;
+static constexpr int BLOCK_START_MEM = 1 << 1;
+static constexpr int BLOCK_END_MEM = 1 << 2;
+
+static constexpr usize BLOCK_MAGIC = 0x6d616c6c6f63210a; // echo 'malloc!' | hexdump -C (includes a newline)
+static constexpr usize BLOCK_DEAD = 0xdeaddeaddeaddead;
+
+static constexpr u8 KMALLOC_SCRUB_BYTE = 0xac;
+static constexpr u8 KFREE_SCRUB_BYTE = 0xde;
+
+static constexpr usize MINIMUM_PAGES_PER_ALLOCATION = 4;
+
+struct HeapBlock : LinkedListNode<HeapBlock>
+{
+    usize req_size;
+    usize full_size;
+    int status;
+    usize magic;
+};
+
+static_assert(sizeof(HeapBlock) == 48UL);
+
+static const isize HEAP_BLOCK_SIZE = 48;
+
+static LinkedList<HeapBlock> heap;
+
+// If we're allocating a large amount of memory, map enough pages for it, but otherwise just use the default amount of
+// pages.
+static usize get_pages_for_allocation(usize bytes)
+{
+    usize pages = get_blocks_from_size(bytes, PAGE_SIZE);
+    if (pages < MINIMUM_PAGES_PER_ALLOCATION) pages = MINIMUM_PAGES_PER_ALLOCATION;
+    return pages;
+}
+
+static bool is_block_free(HeapBlock* block)
+{
+    return !(block->status & BLOCK_USED);
+}
+
+static usize space_available(HeapBlock* block)
+{
+    expect(!is_block_free(block), "Attempting to split a free block");
+    return block->full_size - block->req_size;
+}
+
+// The heap block is stored right behind a memory block.
+static HeapBlock* get_heap_block_for_pointer(void* ptr)
+{
+    return (HeapBlock*)offset_ptr(ptr, -HEAP_BLOCK_SIZE);
+}
+
+static void* get_pointer_from_heap_block(HeapBlock* block)
+{
+    return (void*)offset_ptr(block, HEAP_BLOCK_SIZE);
+}
+
+static usize get_fair_offset_to_split_at(HeapBlock* block, usize min)
+{
+    usize available = space_available(block);
+
+    available -= min; // reserve at least min size for the new block.
+
+    available -= (available /
+                  2); // reserve half of the rest for the new block, while still leaving another half for the old one.
+
+    available = align_down<16>(available); // Everything has to be aligned on a 16-byte boundary
+
+    return available + block->req_size;
+}
+
+static Option<HeapBlock*> split(HeapBlock* block, usize size)
+{
+    const usize available = space_available(block); // How much space can we steal from this block?
+    const usize old_size =
+        block->full_size; // Save the old value of this variable since we are going to use it after modifying it
+
+    if (available < (size + sizeof(HeapBlock)))
+        return {}; // This block hasn't got enough free space to hold the requested size.
+
+    const usize offset = get_fair_offset_to_split_at(block, size + sizeof(HeapBlock));
+    block->full_size = offset; // shrink the old block to fit this offset
+
+    HeapBlock* new_block = offset_ptr(block, offset + sizeof(HeapBlock));
+
+    new_block->magic = BLOCK_MAGIC;
+    new_block->status = (block->status & BLOCK_END_MEM) ? BLOCK_END_MEM : 0;
+    new_block->full_size = old_size - (offset + sizeof(HeapBlock));
+    heap.add_after(block, new_block);
+
+    block->status &= ~BLOCK_END_MEM; // this block is no longer the last block in its memory range
+
+    return new_block;
+}
+
+static Result<void> combine_forward(HeapBlock* block)
+{
+    // This block ends a memory range, cannot be combined with blocks outside its range.
+    if (block->status & BLOCK_END_MEM) return {};
+
+    // The caller needs to ensure there is a next block.
+    HeapBlock* const next = heap.next(block).value();
+    // This block starts a memory range, cannot be combined with blocks outside its range.
+    if (next->status & BLOCK_START_MEM) return {};
+
+    heap.remove(next);
+    next->magic = BLOCK_DEAD;
+
+    if (next->status & BLOCK_END_MEM)
+    {
+        if (next->status & BLOCK_START_MEM)
+        {
+            const usize pages = get_blocks_from_size(next->full_size + sizeof(HeapBlock), PAGE_SIZE);
+            TRY(release_pages_impl(next, pages));
+            return {};
+        }
+        else
+            block->status |= BLOCK_END_MEM;
+    }
+
+    block->full_size += next->full_size + sizeof(HeapBlock);
+
+    return {};
+}
+
+static Result<HeapBlock*> combine_backward(HeapBlock* block)
+{
+    // This block starts a memory range, cannot be combined with blocks outside its range.
+    if (block->status & BLOCK_START_MEM) return block;
+
+    // The caller needs to ensure there is a last block.
+    HeapBlock* const last = heap.previous(block).value();
+    // This block ends a memory range, cannot be combined with blocks outside its range.
+    if (last->status & BLOCK_END_MEM) return block;
+    heap.remove(block);
+    block->magic = BLOCK_DEAD;
+
+    if (block->status & BLOCK_END_MEM)
+    {
+        if (block->status & BLOCK_START_MEM)
+        {
+            const usize pages = get_blocks_from_size(block->full_size + sizeof(HeapBlock), PAGE_SIZE);
+            TRY(release_pages_impl(block, pages));
+            return last;
+        }
+        else
+            last->status |= BLOCK_END_MEM;
+    }
+
+    last->full_size += block->full_size + sizeof(HeapBlock);
+
+    return last;
+}
+
+Result<void*> malloc_impl(usize size, bool should_scrub)
+{
+    if (!size) return (void*)BLOCK_MAGIC;
+
+    size = align_up<16>(size);
+
+    Option<HeapBlock*> block = heap.first();
+    while (block.has_value())
+    {
+        HeapBlock* const current = block.value();
+        // Trying to find a free block...
+        if (is_block_free(current))
+        {
+            if (current->full_size < size)
+            {
+                block = heap.next(current);
+                continue;
+            }
+            break; // We found a free block that's big enough!!
+        }
+        auto rc = split(current, size);
+        if (rc.has_value())
+        {
+            block = rc.value(); // We managed to get a free block from a larger used block!!
+            break;
+        }
+        block = heap.next(current);
+    }
+
+    if (!block.has_value()) // No free blocks, let's allocate a new one
+    {
+        usize pages = get_pages_for_allocation(size + sizeof(HeapBlock));
+        HeapBlock* const current = (HeapBlock*)TRY(allocate_pages_impl(pages));
+
+        current->full_size = (pages * PAGE_SIZE) - sizeof(HeapBlock);
+        current->magic = BLOCK_MAGIC;
+        current->status = BLOCK_START_MEM | BLOCK_END_MEM;
+        heap.append(current);
+
+        block = current;
+    }
+
+    HeapBlock* const current = block.value();
+
+    current->req_size = size;
+    current->status |= BLOCK_USED;
+
+    if (should_scrub) { memset(get_pointer_from_heap_block(current), KMALLOC_SCRUB_BYTE, size); }
+
+    return get_pointer_from_heap_block(current);
+}
+
+Result<void> free_impl(void* ptr)
+{
+    if (ptr == (void*)BLOCK_MAGIC) return {}; // This pointer was returned from a call to malloc(0)
+    if (!ptr) return {};
+
+    HeapBlock* block = get_heap_block_for_pointer(ptr);
+
+    if (block->magic != BLOCK_MAGIC)
+    {
+        if (block->magic == BLOCK_DEAD) { dbgln("ERROR: Attempt to free memory at %p, which was already freed", ptr); }
+        else
+            dbgln("ERROR: Attempt to free memory at %p, which wasn't allocated with kmalloc", ptr);
+
+        return err(EFAULT);
+    }
+
+    if (is_block_free(block))
+    {
+        dbgln("ERROR: Attempt to free memory at %p, which was already freed", ptr);
+        return err(EFAULT);
+    }
+    else
+        block->status &= ~BLOCK_USED;
+
+    memset(ptr, KFREE_SCRUB_BYTE, block->req_size);
+
+    auto maybe_next = heap.next(block);
+    if (maybe_next.has_value() && is_block_free(maybe_next.value()))
+    {
+        // The next block is also free, thus we can merge!
+        TRY(combine_forward(block));
+    }
+
+    auto maybe_last = heap.previous(block);
+    if (maybe_last.has_value() && is_block_free(maybe_last.value()))
+    {
+        // The last block is also free, thus we can merge!
+        block = TRY(combine_backward(block));
+    }
+
+    if ((block->status & BLOCK_START_MEM) && (block->status & BLOCK_END_MEM))
+    {
+        heap.remove(block);
+        const usize pages = get_blocks_from_size(block->full_size + sizeof(HeapBlock), PAGE_SIZE);
+        TRY(release_pages_impl(block, pages));
+    }
+
+    return {};
+}
+
+Result<void*> realloc_impl(void* ptr, usize size)
+{
+    if (!ptr) return malloc_impl(size);
+    if (ptr == (void*)BLOCK_MAGIC) return malloc_impl(size);
+    if (!size)
+    {
+        TRY(free_impl(ptr));
+        return (void*)BLOCK_MAGIC;
+    }
+
+    HeapBlock* const block = get_heap_block_for_pointer(ptr);
+
+    if (block->magic != BLOCK_MAGIC)
+    {
+        if (block->magic == BLOCK_DEAD)
+        {
+            dbgln("ERROR: Attempt to realloc memory at %p, which was already freed", ptr);
+        }
+        else
+            dbgln("ERROR: Attempt to realloc memory at %p, which wasn't allocated with kmalloc", ptr);
+
+        return err(EFAULT);
+    }
+
+    size = align_up<16>(size);
+
+    if (is_block_free(block))
+    {
+        dbgln("ERROR: Attempt to realloc memory at %p, which was already freed", ptr);
+        return err(EFAULT);
+    }
+
+    if (block->full_size >= size)
+    {
+        // This block is already large enough!
+        // FIXME: Scrub this if necessary.
+        block->req_size = size;
+        return ptr;
+    }
+
+    usize old_size = block->req_size;
+
+    void* const new_ptr = TRY(malloc_impl(size, false));
+    memcpy(new_ptr, ptr, old_size > size ? size : old_size);
+    TRY(free_impl(ptr));
+
+    if (old_size < size) { memset(offset_ptr(new_ptr, old_size), KMALLOC_SCRUB_BYTE, size - old_size); }
+
+    return new_ptr;
+}
+
+Result<void*> calloc_impl(usize nmemb, usize size)
+{
+    const usize realsize = TRY(safe_mul(nmemb, size));
+    void* const ptr = TRY(malloc_impl(realsize, false));
+    return memset(ptr, 0, realsize);
+}
+
+void dump_heap_usage()
+{
+    dbgln("-- Dumping usage stats for heap:");
+    if (!heap.count())
+    {
+        dbgln("- Heap is not currently being used");
+        return;
+    }
+    usize alloc_total = 0;
+    usize alloc_used = 0;
+    auto block = heap.first();
+    while (block.has_value())
+    {
+        HeapBlock* current = block.value();
+        if (is_block_free(current))
+        {
+            dbgln("- Available block (%p), of size %zu (%s%s)", (void*)current, current->full_size,
+                  current->status & BLOCK_START_MEM ? "b" : "-", current->status & BLOCK_END_MEM ? "e" : "-");
+            alloc_total += current->full_size + sizeof(HeapBlock);
+        }
+        else
+        {
+            dbgln("- Used block (%p), of size %zu, of which %zu bytes are being used (%s%s)", (void*)current,
+                  current->full_size, current->req_size, current->status & BLOCK_START_MEM ? "b" : "-",
+                  current->status & BLOCK_END_MEM ? "e" : "-");
+            alloc_total += current->full_size + sizeof(HeapBlock);
+            alloc_used += current->req_size;
+        }
+        block = heap.next(current);
+    }
+
+    dbgln("-- Total memory allocated for heap: %zu bytes", alloc_total);
+    dbgln("-- Heap memory in use: %zu bytes", alloc_used);
+}
+
+void* operator new(usize size, const std::nothrow_t&) noexcept
+{
+    return malloc_impl(size).value_or(nullptr);
+}
+
+void* operator new[](usize size, const std::nothrow_t&) noexcept
+{
+    return malloc_impl(size).value_or(nullptr);
+}
+
+void operator delete(void* p) noexcept
+{
+    free_impl(p);
+}
+
+void operator delete[](void* p) noexcept
+{
+    free_impl(p);
+}
+
+void operator delete(void* p, usize) noexcept
+{
+    free_impl(p);
+}
+
+void operator delete[](void* p, usize) noexcept
+{
+    free_impl(p);
+}

luna/src/OwnedStringView.cpp

@@ -23,7 +23,7 @@ OwnedStringView::OwnedStringView(char* c_str)
 
 OwnedStringView::~OwnedStringView()
 {
-    if (m_string) raw_free(m_string);
+    if (m_string) free_impl(m_string);
 }
 
 Result<OwnedStringView> OwnedStringView::clone() const

luna/src/Utf8.cpp

@@ -146,7 +146,7 @@ Result<usize> Utf8StringDecoder::code_points() const
     return len;
 }
 
-Result<void> Utf8StringDecoder::decode(wchar_t* buf, size_t max) const
+Result<void> Utf8StringDecoder::decode(wchar_t* buf, usize max) const
 {
     const char* it = m_str;
 
@@ -165,7 +165,7 @@ Result<void> Utf8StringDecoder::decode(wchar_t* buf, size_t max) const
 
 Result<void> Utf8StringDecoder::decode(wchar_t* buf) const
 {
-    return decode(buf, (size_t)-1);
+    return decode(buf, (usize)-1);
 }
 
 Utf8StringEncoder::Utf8StringEncoder(const wchar_t* str) : m_str(str), m_code_points(wcslen(str))
@@ -186,7 +186,7 @@ Result<usize> Utf8StringEncoder::byte_length() const
     return len;
 }
 
-Result<void> Utf8StringEncoder::encode(char* buf, size_t max) const
+Result<void> Utf8StringEncoder::encode(char* buf, usize max) const
 {
     const wchar_t* it = m_str;
 
@@ -206,7 +206,7 @@ Result<void> Utf8StringEncoder::encode(char* buf, size_t max) const
 
 Result<void> Utf8StringEncoder::encode(char* buf) const
 {
-    return encode(buf, (size_t)-1);
+    return encode(buf, (usize)-1);
 }
 
 Utf8StateDecoder::Utf8StateDecoder() : m_state_len(0), m_state_index(0)