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.

1 files changed, 0 insertions, 172 deletions

diff --git a/LibC/stdlib.cpp b/LibC/stdlib.cpp
index 656bd91ca7..17486f7c25 100644
--- a/LibC/stdlib.cpp
+++ b/LibC/stdlib.cpp
@@ -16,178 +16,6 @@
 
 extern "C" {
 
-#define MALLOC_SCRUB_BYTE 0x85
-#define FREE_SCRUB_BYTE 0x82
-
-struct MallocHeader {
-    uint16_t first_chunk_index;
-    uint16_t chunk_count : 15;
-    bool is_mmap : 1;
-    size_t size;
-};
-
-#define CHUNK_SIZE  32
-#define POOL_SIZE   4 * 1048576
-
-static const size_t malloc_budget = POOL_SIZE;
-static byte s_malloc_map[POOL_SIZE / CHUNK_SIZE / 8];
-static byte* s_malloc_pool;
-
-static uint32_t s_malloc_sum_alloc = 0;
-static uint32_t s_malloc_sum_free = POOL_SIZE;
-
-static bool s_log_malloc = false;
-static bool s_scrub_malloc = true;
-static bool s_scrub_free = true;
-
-void* malloc(size_t size)
-{
-    if (s_log_malloc)
-        dbgprintf("LibC: malloc(%u)\n", size);
-
-    if (size == 0)
-        return nullptr;
-
-    // We need space for the MallocHeader structure at the head of the block.
-    size_t real_size = size + sizeof(MallocHeader);
-
-    if (real_size >= PAGE_SIZE) {
-        auto* memory = mmap(nullptr, real_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
-        if (memory == MAP_FAILED) {
-            fprintf(stderr, "malloc() failed to mmap() for a %u-byte allocation: %s", size, strerror(errno));
-            volatile char* crashme = (char*)0xf007d00d;
-            *crashme = 0;
-            return nullptr;
-        }
-        auto* header = (MallocHeader*)(memory);
-        byte* ptr = ((byte*)header) + sizeof(MallocHeader);
-        header->chunk_count = 0;
-        header->first_chunk_index = 0;
-        header->size = real_size;
-        header->is_mmap = true;
-        return ptr;
-    }
-
-    if (s_malloc_sum_free < real_size) {
-        fprintf(stderr, "malloc(): Out of memory\ns_malloc_sum_free=%u, real_size=%u\n", s_malloc_sum_free, real_size);
-        ASSERT_NOT_REACHED();
-    }
-
-    size_t chunks_needed = real_size / CHUNK_SIZE;
-    if (real_size % CHUNK_SIZE)
-        chunks_needed++;
-
-    size_t chunks_here = 0;
-    size_t first_chunk = 0;
-
-    for (unsigned i = 0; i < (POOL_SIZE / CHUNK_SIZE / 8); ++i) {
-        if (s_malloc_map[i] == 0xff) {
-            // Skip over completely full bucket.
-            chunks_here = 0;
-            continue;
-        }
-
-        // FIXME: This scan can be optimized further with TZCNT.
-        for (unsigned j = 0; j < 8; ++j) {
-            if ((s_malloc_map[i] & (1<<j))) {
-                // This is in use, so restart chunks_here counter.
-                chunks_here = 0;
-                continue;
-            }
-            if (chunks_here == 0) {
-                // Mark where potential allocation starts.
-                first_chunk = i * 8 + j;
-            }
-
-            ++chunks_here;
-
-            if (chunks_here == chunks_needed) {
-                auto* header = (MallocHeader*)(s_malloc_pool + (first_chunk * CHUNK_SIZE));
-                byte* ptr = ((byte*)header) + sizeof(MallocHeader);
-                header->chunk_count = chunks_needed;
-                header->first_chunk_index = first_chunk;
-                header->is_mmap = false;
-                header->size = size;
-
-                for (size_t k = first_chunk; k < (first_chunk + chunks_needed); ++k)
-                    s_malloc_map[k / 8] |= 1 << (k % 8);
-
-                s_malloc_sum_alloc += header->chunk_count * CHUNK_SIZE;
-                s_malloc_sum_free  -= header->chunk_count * CHUNK_SIZE;
-
-                if (s_scrub_malloc)
-                    memset(ptr, MALLOC_SCRUB_BYTE, (header->chunk_count * CHUNK_SIZE) - sizeof(MallocHeader));
-                return ptr;
-            }
-        }
-    }
-
-    fprintf(stderr, "malloc(): Out of memory (no consecutive chunks found for size %u)\n", size);
-    volatile char* crashme = (char*)0xc007d00d;
-    *crashme = 0;
-    return nullptr;
-}
-
-void free(void* ptr)
-{
-    if (!ptr)
-        return;
-
-    auto* header = (MallocHeader*)((((byte*)ptr) - sizeof(MallocHeader)));
-    if (header->is_mmap) {
-        int rc = munmap(header, header->size);
-        if (rc < 0)
-            fprintf(stderr, "free(): munmap(%p) for allocation %p with size %u failed: %s\n", header, ptr, header->size, strerror(errno));
-        return;
-    }
-
-    for (int i = header->first_chunk_index; i < (header->first_chunk_index + header->chunk_count); ++i)
-        s_malloc_map[i / 8] &= ~(1 << (i % 8));
-
-    s_malloc_sum_alloc -= header->chunk_count * CHUNK_SIZE;
-    s_malloc_sum_free += header->chunk_count * CHUNK_SIZE;
-
-    if (s_scrub_free)
-        memset(header, FREE_SCRUB_BYTE, header->chunk_count * CHUNK_SIZE);
-}
-
-void __malloc_init()
-{
-    s_malloc_pool = (byte*)mmap(nullptr, malloc_budget, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
-    int rc = set_mmap_name(s_malloc_pool, malloc_budget, "malloc pool");
-    if (rc < 0)
-        perror("set_mmap_name failed");
-
-    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;
-}
-
-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);
-    auto* header = (MallocHeader*)((((byte*)ptr) - sizeof(MallocHeader)));
-    size_t old_size = header->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;
-}
-
 typedef void(*__atexit_handler)();
 static int __atexit_handler_count = 0;
 static __atexit_handler __atexit_handlers[32];