X-Git-Url: https://scm.lunaixsky.com/lunaix-os.git/blobdiff_plain/d07db7c15d6cf9d6c0fd07ea29cca77a89b02a79..48b4a227035048fdebcd32532deb7a857c6199ac:/lunaix-os/kernel/mm/kalloc.c

diff --git a/lunaix-os/kernel/mm/kalloc.c b/lunaix-os/kernel/mm/kalloc.c
index c932bb5..91905b4 100644
--- a/lunaix-os/kernel/mm/kalloc.c
+++ b/lunaix-os/kernel/mm/kalloc.c
@@ -1,38 +1,259 @@
+/**
+ * @file kalloc.c
+ * @author Lunaixsky
+ * @brief Implicit free list implementation of malloc family, for kernel use.
+ * 
+ * This version of code is however the simplest and yet insecured, thread unsafe
+ * it just to demonstrate how the malloc/free works behind the curtain
+ * @version 0.1
+ * @date 2022-03-05
+ * 
+ * @copyright Copyright (c) 2022
+ * 
+ */
 #include <lunaix/mm/kalloc.h>
 #include <lunaix/mm/dmm.h>
 
-#include <libc/string.h>
+#include <lunaix/common.h>
+#include <lunaix/spike.h>
+
+#include <klibc/string.h>
 
 #include <stdint.h>
 
 extern uint8_t __kernel_heap_start;
 
-heap_context_t __kalloc_kheap;
+void*
+lx_malloc_internal(heap_context_t* heap, size_t size);
+
+void
+place_chunk(uint8_t* ptr, size_t size);
+
+void
+lx_free_internal(void* ptr);
+
+void*
+coalesce(uint8_t* chunk_ptr);
+
+void*
+lx_grow_heap(heap_context_t* heap, size_t sz);
+
+/*
+    At the beginning, we allocate an empty page and put our initial marker
+    
+    | 4/1 | 0/1 |
+    ^     ^ brk
+    start
+
+    Then, expand the heap further, with HEAP_INIT_SIZE (evaluated to 4096, i.e., 1 pg size)
+    This will allocate as much pages and override old epilogue marker with a free region hdr
+        and put new epilogue marker. These are handled by lx_grow_heap which is internally used
+        by alloc to expand the heap at many moment when needed.
+    
+    | 4/1 | 4096/0 |   .......   | 4096/0 | 0/1 |
+    ^     ^ brk_old                       ^
+    start                                 brk
+
+    Note: the brk always point to the beginning of epilogue.
+*/
 
 int
 kalloc_init() {
-    __kalloc_kheap.start = &__kernel_heap_start;
-    __kalloc_kheap.brk = 0;
+    heap_context_t* kheap = &__current->mm.k_heap;
+    kheap->start = &__kernel_heap_start;
+    kheap->brk = NULL;
+    kheap->max_addr = (void*)KSTACK_START;
+
+    if (!dmm_init(kheap)) {
+        return 0;
+    }
+
+    SW(kheap->start, PACK(4, M_ALLOCATED));
+    SW(kheap->start + WSIZE, PACK(0, M_ALLOCATED));
+    kheap->brk += WSIZE;
 
-    return dmm_init(&__kalloc_kheap);
+    return lx_grow_heap(kheap, HEAP_INIT_SIZE) != NULL;
 }
 
 void*
-kmalloc(size_t size) {
-    return lx_malloc(&__kalloc_kheap, size);
+lxmalloc(size_t size) {
+    return lx_malloc_internal(&__current->mm.k_heap, size);
 }
 
 void*
-kcalloc(size_t size) {
-    void* ptr = kmalloc(size);
+lxcalloc(size_t n, size_t elem) {
+    size_t pd = n * elem;
+
+    // overflow detection
+    if (pd < elem || pd < n) {
+        return NULL;
+    }
+
+    void* ptr = lxmalloc(pd);
     if (!ptr) {
         return NULL;
     }
 
-    return memset(ptr, 0, size);
+    return memset(ptr, 0, pd);
 }
 
 void
-kfree(void* ptr) {
-    lx_free(ptr);
+lxfree(void* ptr) {
+    if (!ptr) {
+        return;
+    }
+
+    uint8_t* chunk_ptr = (uint8_t*)ptr - WSIZE;
+    uint32_t hdr = LW(chunk_ptr);
+    size_t sz = CHUNK_S(hdr);
+    uint8_t* next_hdr = chunk_ptr + sz;
+
+    // make sure the ptr we are 'bout to free makes sense
+    //   the size trick is stolen from glibc's malloc/malloc.c:4437 ;P
+    
+    assert_msg(((uintptr_t)ptr < (uintptr_t)(-sz)) && !((uintptr_t)ptr & 0x3),
+               "free(): invalid pointer");
+    
+    assert_msg(sz > WSIZE,
+               "free(): invalid size");
+
+    SW(chunk_ptr, hdr & ~M_ALLOCATED);
+    SW(FPTR(chunk_ptr, sz), hdr & ~M_ALLOCATED);
+    SW(next_hdr, LW(next_hdr) | M_PREV_FREE);
+    
+    coalesce(chunk_ptr);
+}
+
+
+void*
+lx_malloc_internal(heap_context_t* heap, size_t size)
+{
+    // Simplest first fit approach.
+
+    if (!size) {
+        return NULL;
+    }
+
+    uint8_t* ptr = heap->start;
+    // round to largest 4B aligned value
+    //  and space for header
+    size = ROUNDUP(size + WSIZE, BOUNDARY);
+    while (ptr < (uint8_t*)heap->brk) {
+        uint32_t header = *((uint32_t*)ptr);
+        size_t chunk_size = CHUNK_S(header);
+        if (!chunk_size && CHUNK_A(header)) {
+            break;
+        }
+        if (chunk_size >= size && !CHUNK_A(header)) {
+            // found!
+            place_chunk(ptr, size);
+            return BPTR(ptr);
+        }
+        ptr += chunk_size;
+    }
+
+    // if heap is full (seems to be!), then allocate more space (if it's
+    // okay...)
+    if ((ptr = lx_grow_heap(heap, size))) {
+        place_chunk(ptr, size);
+        return BPTR(ptr);
+    }
+
+    // Well, we are officially OOM!
+    return NULL;
+}
+
+void
+place_chunk(uint8_t* ptr, size_t size)
+{
+    uint32_t header = *((uint32_t*)ptr);
+    size_t chunk_size = CHUNK_S(header);
+    *((uint32_t*)ptr) = PACK(size, CHUNK_PF(header) | M_ALLOCATED);
+    uint8_t* n_hdrptr = (uint8_t*)(ptr + size);
+    uint32_t diff = chunk_size - size;
+
+    if (!diff) {
+        // if the current free block is fully occupied
+        uint32_t n_hdr = LW(n_hdrptr);
+        // notify the next block about our avaliability
+        SW(n_hdrptr, n_hdr & ~0x2);
+    } else {
+        // if there is remaining free space left
+        uint32_t remainder_hdr = PACK(diff, M_NOT_ALLOCATED | M_PREV_ALLOCATED);
+        SW(n_hdrptr, remainder_hdr);
+        SW(FPTR(n_hdrptr, diff), remainder_hdr);
+
+        /*
+            | xxxx |      |         |
+
+                        |
+                        v
+                        
+            | xxxx |                |
+        */
+        coalesce(n_hdrptr);
+    }
+}
+
+void*
+coalesce(uint8_t* chunk_ptr)
+{
+    uint32_t hdr = LW(chunk_ptr);
+    uint32_t pf = CHUNK_PF(hdr);
+    uint32_t sz = CHUNK_S(hdr);
+
+    uint32_t n_hdr = LW(chunk_ptr + sz);
+
+    if (CHUNK_A(n_hdr) && pf) {
+        // case 1: prev is free
+        uint32_t prev_ftr = LW(chunk_ptr - WSIZE);
+        size_t prev_chunk_sz = CHUNK_S(prev_ftr);
+        uint32_t new_hdr = PACK(prev_chunk_sz + sz, CHUNK_PF(prev_ftr));
+        SW(chunk_ptr - prev_chunk_sz, new_hdr);
+        SW(FPTR(chunk_ptr, sz), new_hdr);
+        chunk_ptr -= prev_chunk_sz;
+    } else if (!CHUNK_A(n_hdr) && !pf) {
+        // case 2: next is free
+        size_t next_chunk_sz = CHUNK_S(n_hdr);
+        uint32_t new_hdr = PACK(next_chunk_sz + sz, pf);
+        SW(chunk_ptr, new_hdr);
+        SW(FPTR(chunk_ptr, sz + next_chunk_sz), new_hdr);
+    } else if (!CHUNK_A(n_hdr) && pf) {
+        // case 3: both free
+        uint32_t prev_ftr = LW(chunk_ptr - WSIZE);
+        size_t next_chunk_sz = CHUNK_S(n_hdr);
+        size_t prev_chunk_sz = CHUNK_S(prev_ftr);
+        uint32_t new_hdr =
+          PACK(next_chunk_sz + prev_chunk_sz + sz, CHUNK_PF(prev_ftr));
+        SW(chunk_ptr - prev_chunk_sz, new_hdr);
+        SW(FPTR(chunk_ptr, sz + next_chunk_sz), new_hdr);
+        chunk_ptr -= prev_chunk_sz;
+    }
+
+    // (fall through) case 4: prev and next are not free
+    return chunk_ptr;
+}
+
+
+void*
+lx_grow_heap(heap_context_t* heap, size_t sz)
+{
+    void* start;
+
+    // The "+ WSIZE" capture the overhead for epilogue marker
+    if (!(start = lxbrk(heap, sz + WSIZE))) {
+        return NULL;
+    }
+    sz = ROUNDUP(sz, BOUNDARY);
+
+    // minus the overhead for epilogue, keep the invariant.
+    heap->brk -= WSIZE;
+
+    uint32_t old_marker = *((uint32_t*)start);
+    uint32_t free_hdr = PACK(sz, CHUNK_PF(old_marker));
+    SW(start, free_hdr);
+    SW(FPTR(start, sz), free_hdr);
+    SW(NEXT_CHK(start), PACK(0, M_ALLOCATED | M_PREV_FREE));
+
+    return coalesce(start);
 }
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