Malloc

A custom implementation of the malloc, free, and realloc functions in C, mimicking the behavior of the standard C library allocator, built using low-level system calls and zone-based memory management.

Project Description

This project reimplements the core dynamic memory allocation routines (malloc, free, realloc) without using the standard library's allocator. The allocator uses:

• mmap for allocating and freeing memory pages.
• Zone-based allocation strategy, where:
  • TINY allocations go in preallocated TINY zones
  • SMALL allocations go in SMALL zones
  • LARGE allocations use separate mmaped regions
• Thread safety via pthread_mutex to ensure consistent access to allocation metadata.
• Custom memory visualization with show_alloc_mem() and show_alloc_mem_ex() for debugging.

This memory allocator is preloadable and can be used to override standard allocation in existing binaries via environment variables like DYLD_INSERT_LIBRARIES or LD_PRELOAD.

Features

• Custom malloc, free, and realloc (replaces libc)
• Zone allocator for TINY, SMALL, and LARGE blocks
• Page alignment via getpagesize()
• Memory usage visualization:
  • show_alloc_mem(): simple block display
  • show_alloc_mem_ex(): detailed view with free/used tracking
• Thread-safe with global mutex
• Performance-optimized: minimizes mmap calls
• Supports dynamic preloading via .so file

Build Instructions

make test

Output

cc -Wall -Wextra -Werror -I includes main.c -L. -lft_malloc -o test_malloc
[+] Running test with DYLD_INSERT_LIBRARIES
DYLD_INSERT_LIBRARIES=./libft_malloc.so DYLD_FORCE_FLAT_NAMESPACE=1 ./test_malloc
======== Test: Basic ft_malloc ========
a: hello world
b: this is a small block

======== ft_show_alloc_mem() ========
LARGE : 0x102a60000
0x102a60040 - 0x102a60c00 : 3008 bytes
TINY : 0x102a50000
0x102a50040 - 0x102a500c0 : 128 bytes
TINY : 0x102a40000
0x102a40040 - 0x102a40080 : 64 bytes
Total : 3200 bytes

======== Test: ft_free() + defrag ========

======== ft_show_alloc_mem_ex() ========
LARGE ZONE @ 0x102a60000 | total zone size: 3072 bytes
  [ft_free] 0x102a60040 - 0x102a60c00 : 3008 bytes
TINY ZONE @ 0x102a50000 | total zone size: 65536 bytes
  [ft_free] 0x102a50040 - 0x102a500c0 : 128 bytes
TINY ZONE @ 0x102a40000 | total zone size: 65536 bytes
  [ft_free] 0x102a40040 - 0x102a40080 : 64 bytes
TOTAL USED : 0 bytes
TOTAL ft_free : 3200 bytes

======== Test: ft_realloc() ========
x after ft_realloc: realloc me

======== Final ft_show_alloc_mem_ex() ========
LARGE ZONE @ 0x102a60000 | total zone size: 3072 bytes
  [ft_free] 0x102a60040 - 0x102a60c00 : 3008 bytes
TINY ZONE @ 0x102a50000 | total zone size: 65536 bytes
  [USED] 0x102a50040 - 0x102a500c0 : 128 bytes
TINY ZONE @ 0x102a40000 | total zone size: 65536 bytes
  [ft_free] 0x102a40040 - 0x102a40080 : 64 bytes
TOTAL USED : 128 bytes
TOTAL ft_free : 3072 bytes

Disclaimer

This project was developed just for fun out of 42 school supervision, please don't rely on it blindly for your school work.