diff --git a/cmd.py b/cmd.py
index c15aa80..7cef1a4 100644
--- a/cmd.py
+++ b/cmd.py
@@ -289,6 +289,16 @@ def build(key):
                     "-o", "./bin/bst"
                 ],
             ],
+        "malloc" : [
+                [
+                    "/usr/bin/gcc-7", 
+                    "-Wall", "-g", "-O0", "-Werror", "-std=gnu99", "-Wno-unused-but-set-variable", "-Wno-unused-variable", "-Wno-unused-function",
+                    "-I", "./src",
+                    "-DDEBUG_MALLOC",
+                    "./src/mains/mem_alloc.c",
+                    "-o", "./bin/malloc"
+                ],
+            ],
     }
 
     if not key in gcc_map:
@@ -308,6 +318,7 @@ def run(key):
         "rb" : ["./bin/rb"],
         "trie" : ["./bin/trie"],
         "bst" : ["./bin/bst"],
+        "malloc" : ["./bin/malloc"],
     }
     if not key in bin_map:
         print("input the correct binary key:", bin_map.keys())
diff --git a/src/mains/mem_alloc.c b/src/mains/mem_alloc.c
new file mode 100644
index 0000000..8e1331a
--- /dev/null
+++ b/src/mains/mem_alloc.c
@@ -0,0 +1,264 @@
+/* BCST - Introduction to Computer Systems
+ * Author:      yangminz@outlook.com
+ * Github:      https://github.com/yangminz/bcst_csapp
+ * Bilibili:    https://space.bilibili.com/4564101
+ * Zhihu:       https://www.zhihu.com/people/zhao-yang-min
+ * This project (code repository and videos) is exclusively owned by yangminz 
+ * and shall not be used for commercial and profitting purpose 
+ * without yangminz's permission.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+int heap_init();
+uint64_t mem_alloc(uint32_t size);
+void mem_free(uint64_t vaddr);
+
+uint64_t heap_start_vaddr = 0;
+uint64_t heap_end_vaddr = 0;
+
+#define HEAP_MAX_SIZE (4096 * 8)
+uint8_t heap[HEAP_MAX_SIZE];
+
+// Round up to next multiple of n:
+// if (x == k * n)
+// return x
+// else, x = k * n + m and m < n
+// return (k + 1) * n
+static uint64_t round_up(uint64_t x, uint64_t n)
+{
+    return n * ((x + n - 1) / n);
+}
+
+// applicapable for both header & footer
+static uint32_t get_blocksize(uint64_t header_vaddr)
+{
+    assert(heap_start_vaddr <= header_vaddr && header_vaddr <= heap_end_vaddr);
+    assert(header_vaddr & 0x3 == 0x0);  // header & footer should be 4 bytes alignment
+
+    uint32_t header_value = *(uint32_t *)&heap[header_vaddr];
+    return header_value & 0xFFFFFFF8;
+}
+
+// applicapable for both header & footer
+static void set_blocksize(uint64_t header_vaddr, uint32_t blocksize)
+{
+    assert(heap_start_vaddr <= header_vaddr && header_vaddr <= heap_end_vaddr);
+    assert(header_vaddr & 0x3 == 0x0);  // header & footer should be 4 bytes alignment
+    assert(blocksize & 0x7 == 0x0); // blocksize should be 8 bytes aligned
+
+    *(uint32_t *)&heap[header_vaddr] &= 0x00000007;
+    *(uint32_t *)&heap[header_vaddr] |= blocksize;
+}
+
+// applicapable for both header & footer
+static uint32_t get_allocated(uint64_t header_vaddr)
+{
+    assert(heap_start_vaddr <= header_vaddr && header_vaddr <= heap_end_vaddr);
+    assert(header_vaddr & 0x3 == 0x0);  // header & footer should be 4 bytes alignment
+
+    uint32_t header_value = *(uint32_t *)&heap[header_vaddr];
+    return header_value & 0x1;    
+}
+
+// applicapable for both header & footer
+static void set_allocated(uint64_t header_vaddr, uint32_t allocated)
+{
+    assert(heap_start_vaddr <= header_vaddr && header_vaddr <= heap_end_vaddr);
+    assert(header_vaddr & 0x3 == 0x0);  // header & footer should be 4 bytes alignment
+
+    *(uint32_t *)&heap[header_vaddr] &= 0xFFFFFFF8;
+    *(uint32_t *)&heap[header_vaddr] |= (allocated & 0x1);
+}
+
+static uint64_t get_payload(uint64_t vaddr)
+{
+    // vaddr can be:
+    // 1. starting address of the block (8 * n + 4)
+    // 2. starting address of the payload (8 * m)
+    return round_up(vaddr, 8);
+}
+
+static uint64_t get_blockheader(uint64_t vaddr)
+{
+    // vaddr can be:
+    // 1. starting address of the block (8 * n + 4)
+    // 2. starting address of the payload (8 * m)
+    return round_up(vaddr, 8) - 4;
+}
+
+static uint64_t get_nextheader(uint64_t vaddr)
+{
+    // vaddr can be:
+    // 1. starting address of the block (8 * n + 4)
+    // 2. starting address of the payload (8 * m)
+    uint64_t header_vaddr = get_blockheader(vaddr);
+    uint32_t block_size = get_blocksize(header_vaddr);
+
+    uint64_t next_header_vaddr = header_vaddr + block_size;
+    assert(heap_start_vaddr <= next_header_vaddr &&
+        next_header_vaddr <= heap_end_vaddr);
+    
+    return next_header_vaddr;
+}
+
+static uint64_t get_prevheader(uint64_t vaddr)
+{
+    // vaddr can be:
+    // 1. starting address of the block (8 * n + 4)
+    // 2. starting address of the payload (8 * m)
+    uint64_t header_vaddr = get_blockheader(vaddr);
+    assert(header_vaddr >= 16);
+
+    uint64_t prev_footer_vaddr = header_vaddr - 4;
+    uint32_t prev_blocksize = get_blocksize(prev_footer_vaddr);
+
+    uint64_t prev_header_vaddr = header_vaddr - prev_blocksize;
+    assert(heap_start_vaddr <= prev_header_vaddr &&
+        prev_header_vaddr <= heap_end_vaddr - 12);
+    
+    return prev_header_vaddr;
+}
+
+static int heap_check()
+{
+    // rule 1: block[0] ==> A/F
+    // rule 2: block[-1] ==> A/F
+    // rule 3: block[i] == A ==> block[i-1] == A/F && block[i+1] == A/F
+    // rule 4: block[i] == F ==> block[i-1] == A && block[i+1] == A
+    // these 4 rules ensures that
+    // adjacent free blocks are always merged together
+    // henceforth external fragmentation are minimized
+    return 0;
+}
+
+int heap_init()
+{
+    // heap_start_vaddr is the starting address of the first block
+    // the payload of the first block is 8B aligned ([8])
+    // so the header address of the first block is [8] - 4 = [4]
+    heap_start_vaddr = 4;
+
+    set_blocksize(heap_start_vaddr, 4096 - 8);
+    set_allocated(heap_start_vaddr, 0);
+
+    // we do not set footer for the last block in heap
+    heap_end_vaddr = 4096 - 1;
+
+    return 0;
+}
+
+// size - requested payload size
+// return - the virtual address of payload
+uint64_t mem_alloc(uint32_t size)
+{
+    uint32_t request_blocksize = round_up(size, 8) + 4 + 4;
+
+    uint64_t b = heap_start_vaddr;
+    while (b <= heap_end_vaddr)
+    {
+        uint32_t b_blocksize = get_blocksize(b);
+        uint32_t b_allocated = get_allocated(b);
+
+        if (b_allocated == 0 && b_blocksize >= request_blocksize)
+        {
+            // allocate this block
+            if (b_blocksize > request_blocksize)
+            {
+                // split this block `b`
+                // b_blocksize - request_blocksize >= 8
+                set_allocated(b, 1);
+                set_blocksize(b, request_blocksize);
+
+                // set the left splitted block
+                // in the extreme situation, next block size == 8
+                // which makes the whole block of next to be:
+                // [0x00000008, 0x00000008]
+                uint64_t next_header_vaddr = b + request_blocksize;
+                set_allocated(next_header_vaddr, 0);
+                set_blocksize(next_header_vaddr, b_blocksize - request_blocksize);
+
+                return get_payload(b);
+            }
+            else
+            {
+                // no need to split this block
+                // set_blocksize(b, request_blocksize);
+                set_allocated(b, 1);
+                return get_payload(b);
+            }
+        }
+        else
+        {
+            // go to next block
+            b = get_nextheader(b);
+        }
+    }
+
+    // <==> return NULL;
+    return 0;
+}
+
+void mem_free(uint64_t vaddr)
+{
+    assert(heap_start_vaddr <= vaddr && vaddr <= heap_end_vaddr);
+    assert(vaddr & 0x7 == 0x0);
+
+    uint64_t req = get_blockheader(vaddr);
+    uint32_t req_allocated = get_allocated(req);
+    uint32_t req_blocksize = get_blocksize(req);
+    assert(req_allocated == 1);
+
+    // block starting address of next & prev blocks
+    // TODO: corner case - req can be the first or last block
+    uint64_t next = get_nextheader(vaddr);
+    uint64_t prev = get_prevheader(vaddr);
+
+    uint32_t next_allocated = get_allocated(next);
+    uint32_t prev_allocated = get_allocated(prev);
+
+    uint32_t next_blocksize = get_blocksize(next);
+    uint32_t prev_blocksize = get_blocksize(prev);
+
+    if (next_allocated == 1 && prev_allocated == 1)
+    {
+        // case 1: *A(A->F)A*
+        // ==> *AFA*
+        set_allocated(req, 0);
+    }
+    else if (next_allocated == 0 && prev_allocated == 1)
+    {
+        // case 2: *A(A->F)FA
+        // ==> *AFFA ==> *A[FF]A merge current and next
+        set_allocated(req, 0);
+        set_blocksize(req, req_blocksize + next_blocksize);
+    }
+    else if (next_allocated == 1 && prev_allocated == 0)
+    {
+        // case 3: AF(A->F)A*
+        // ==> AFFA* ==> A[FF]A* merge current and prev
+        set_allocated(prev, 0);
+        set_blocksize(prev, req_blocksize + prev_blocksize);
+    }
+    else
+    {
+        // case 4: AF(A->F)FA
+        // ==> AFFFA ==> A[FFF]A merge current and prev and next
+        set_allocated(prev, 0);
+        set_blocksize(prev, req_blocksize + prev_blocksize + next_blocksize);
+    }
+}
+
+#ifdef DEBUG_MALLOC
+int main()
+{
+    printf("malloc!\n");
+
+    heap_init();
+
+    return 0;
+}
+#endif
\ No newline at end of file