LibC: Implement a simple freelist-based malloc() with size classes.

It's not thread-safe yet, and there is lots of room for improvement.
Still it's a lot faster than the first-fit bitmap-based one it replaces.

LibC/Makefile

@@ -17,6 +17,7 @@ LIBC_OBJS = \
        strings.o \
        mman.o \
        dirent.o \
+       malloc.o \
        stdlib.o \
        time.o \
        utsname.o \
@@ -84,4 +85,4 @@ install: $(LIBRARY)
 	cp $(LIBRARY) ../Base/usr/lib
 	cp crt0.o ../Base/usr/lib/
 	cp crti.ao ../Base/usr/lib/crti.o
-	cp crtn.ao ../Base/usr/lib/crtn.o
+	cp crtn.ao ../Base/usr/lib/crtn.o

LibC/malloc.cpp

@@ -0,0 +1,228 @@
+#include <AK/Bitmap.h>
+#include <AK/InlineLinkedList.h>
+#include <sys/mman.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <stdio.h>
+#include <serenity.h>
+
+// FIXME: Thread safety.
+
+//#define MALLOC_DEBUG
+#define MALLOC_SCRUB_BYTE 0x85
+#define FREE_SCRUB_BYTE 0x82
+#define MAGIC_PAGE_HEADER 0x42657274
+#define MAGIC_BIGALLOC_HEADER 0x42697267
+#define PAGE_ROUND_UP(x) ((((size_t)(x)) + PAGE_SIZE-1) & (~(PAGE_SIZE-1)))
+
+static bool s_log_malloc = false;
+static bool s_scrub_malloc = true;
+static bool s_scrub_free = true;
+static unsigned short size_classes[] = { 8, 16, 32, 64, 128, 252, 508, 1016, 2036, 0 };
+static constexpr size_t num_size_classes = sizeof(size_classes) / sizeof(unsigned short);
+
+struct CommonHeader {
+    size_t m_magic;
+    size_t m_size;
+};
+
+struct BigAllocationBlock : public CommonHeader {
+    BigAllocationBlock(size_t size)
+    {
+        m_magic = MAGIC_BIGALLOC_HEADER;
+        m_size = size;
+    }
+    unsigned char* m_slot[0];
+};
+
+struct FreelistEntry {
+    FreelistEntry* next;
+};
+
+struct ChunkedBlock : public CommonHeader, public InlineLinkedListNode<ChunkedBlock> {
+    ChunkedBlock(size_t bytes_per_chunk)
+    {
+        m_magic = MAGIC_PAGE_HEADER;
+        m_size = bytes_per_chunk;
+        m_free_chunks = chunk_capacity();
+        m_freelist = (FreelistEntry*)chunk(0);
+        for (size_t i = 0; i < chunk_capacity(); ++i) {
+            auto* entry = (FreelistEntry*)chunk(i);
+            if (i != chunk_capacity() - 1)
+                entry->next = (FreelistEntry*)chunk(i + 1);
+            else
+                entry->next = nullptr;
+        }
+
+    }
+
+    ChunkedBlock* m_prev { nullptr };
+    ChunkedBlock* m_next { nullptr };
+    FreelistEntry* m_freelist { nullptr };
+
+    unsigned short m_free_chunks { 0 };
+
+    unsigned char m_slot[0];
+
+    void* chunk(int index)
+    {
+        return &m_slot[index * m_size];
+    }
+    size_t bytes_per_chunk() const { return m_size; }
+    size_t free_chunks() const { return m_free_chunks; }
+    size_t used_chunks() const { return chunk_capacity() - m_free_chunks; }
+    size_t chunk_capacity() const { return (PAGE_SIZE - sizeof(ChunkedBlock)) / m_size; }
+};
+
+static InlineLinkedList<ChunkedBlock> g_allocators[num_size_classes];
+
+static InlineLinkedList<ChunkedBlock>* allocator_for_size(size_t size, size_t& good_size)
+{
+    for (int i = 0; size_classes[i]; ++i) {
+        if (size <= size_classes[i]) {
+            good_size = size_classes[i];
+            return &g_allocators[i];
+        }
+    }
+    good_size = PAGE_ROUND_UP(size);
+    return nullptr;
+}
+
+extern "C" {
+
+size_t malloc_good_size(size_t size)
+{
+    for (int i = 0; size_classes[i]; ++i) {
+        if (size < size_classes[i])
+            return size_classes[i];
+    }
+    return PAGE_ROUND_UP(size);
+}
+
+static void* os_alloc(size_t size)
+{
+    return mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
+}
+
+static void os_free(void* ptr, size_t size)
+{
+    int rc = munmap(ptr, size);
+    assert(rc == 0);
+}
+
+void* malloc(size_t size)
+{
+    if (s_log_malloc)
+        dbgprintf("LibC: malloc(%u)\n", size);
+
+    if (!size)
+        return nullptr;
+
+    size_t good_size;
+    auto* allocator = allocator_for_size(size, good_size);
+
+    if (!allocator) {
+        size_t real_size = sizeof(BigAllocationBlock) + size;
+        void* page_ptr = os_alloc(real_size);
+        BigAllocationBlock* bigalloc_header = new (page_ptr) BigAllocationBlock(real_size);
+        return &bigalloc_header->m_slot[0];
+    }
+    assert(allocator);
+
+    ChunkedBlock* block = nullptr;
+    for (block = allocator->head(); block; block = block->next()) {
+        if (block->free_chunks())
+            break;
+    }
+
+    if (!block) {
+        block = (ChunkedBlock*)os_alloc(PAGE_SIZE);
+        char buffer[64];
+        snprintf(buffer, sizeof(buffer), "malloc() page (%u)", good_size);
+        set_mmap_name(block, PAGE_SIZE, buffer);
+        new (block) ChunkedBlock(good_size);
+        allocator->append(block);
+    }
+
+    --block->m_free_chunks;
+    void* ptr = block->m_freelist;
+    block->m_freelist = block->m_freelist->next;
+#ifdef MALLOC_DEBUG
+    dbgprintf("LibC: allocated %p (chunk %d in allocator %p, size %u)\n", ptr, index, page, page->bytes_per_chunk());
+#endif
+    if (s_scrub_malloc)
+        memset(ptr, MALLOC_SCRUB_BYTE, block->m_size);
+    return ptr;
+
+    ASSERT_NOT_REACHED();
+}
+
+void free(void* ptr)
+{
+    if (!ptr)
+        return;
+
+    void* page_base = (void*)((uintptr_t)ptr & (uintptr_t)~0xfff);
+    size_t magic = *(size_t*)page_base;
+
+    if (magic == MAGIC_BIGALLOC_HEADER) {
+        auto* header = (BigAllocationBlock*)page_base;
+        os_free(header, header->m_size);
+        return;
+    }
+
+    assert(magic == MAGIC_PAGE_HEADER);
+    auto* page = (ChunkedBlock*)page_base;
+
+#ifdef MALLOC_DEBUG
+    dbgprintf("LibC: freeing %p in allocator %p (size=%u, used=%u)\n", ptr, page, page->bytes_per_chunk(), page->used_chunks());
+#endif
+
+    if (s_scrub_free)
+        memset(ptr, FREE_SCRUB_BYTE, page->bytes_per_chunk());
+
+    auto* entry = (FreelistEntry*)ptr;
+    entry->next = page->m_freelist;
+    page->m_freelist = entry;
+
+    ++page->m_free_chunks;
+}
+
+void* calloc(size_t count, size_t size)
+{
+    size_t new_size = count * size;
+    auto* ptr = malloc(new_size);
+    memset(ptr, 0, new_size);
+    return ptr;
+}
+
+void* realloc(void* ptr, size_t size)
+{
+    if (!ptr)
+        return malloc(size);
+
+    size_t old_size = 0;
+    void* page_base = (void*)((uintptr_t)ptr & (uintptr_t)~0xfff);
+    auto* header = (const CommonHeader*)page_base;
+    old_size = header->m_size;
+
+    if (size == old_size)
+        return ptr;
+    auto* new_ptr = malloc(size);
+    memcpy(new_ptr, ptr, min(old_size, size));
+    free(ptr);
+    return new_ptr;
+}
+
+void __malloc_init()
+{
+    if (getenv("LIBC_NOSCRUB_MALLOC"))
+        s_scrub_malloc = false;
+    if (getenv("LIBC_NOSCRUB_FREE"))
+        s_scrub_free = false;
+    if (getenv("LIBC_LOG_MALLOC"))
+        s_log_malloc = true;
+}
+
+}
+