Malloc Library

Description

The Malloc Library is a custom implementation of standard memory management functions in C: malloc, free, calloc, and realloc. This project aims to deepen the understanding of dynamic memory allocation, pointer manipulation, and system-level programming.

Features

• malloc: Allocates a block of memory of a specified size.
• free: Releases a previously allocated block of memory.
• calloc: Allocates and zeroes multiple blocks of memory.
• realloc: Resizes an existing memory block while preserving its data if possible.
• Bucket-based allocation: Uses fixed-size buckets to minimize fragmentation.
• Optimized alignment: Ensures blocks are aligned to long double for better performance.
• Automatic page release: Unmaps empty pages using munmap.
• LD_PRELOAD compatible: Can replace malloc in external programs.

Project Structure

malloc/
├── src/
│   ├── bucket.c        # Bucket management for memory blocks
│   ├── malloc.c        # Public interface for malloc, free, realloc, calloc
│   ├── my_malloc.c     # Core implementation of the memory allocator
│   ├── utils.c         # Utility functions (alignment, page management, etc.)
│   ├── bucket.h        # Header for bucket structures
│   ├── my_malloc.h     # Header for memory functions
│   ├── utils.h         # Header for utility functions
│   ├── Makefile        # Build system for compiling the library
├── tests/            # Provided test binaries for verification
│   ├── corruptionproof     # Tests metadata integrity
│   ├── memoryfootprint     # Tests memory efficiency
│   ├── speed              # Tests allocator performance
└── README.md         # This file!

Getting Started

Prerequisites

• GCC or another compatible C compiler.
• A Unix-based system is recommended for testing (Linux, macOS).

Clone the Repository

git clone https://github.com/remicku/Malloc-Library.git
cd Malloc-Library

Compilation

A Makefile is provided to simplify the build process. Compile the code by running:

make all

Available targets:

• all: Compiles the library and examples.
• library: Compiles the library
• clean: Removes all compiled files.
• debug: Enables debugging with gdb.

To clean the project:

make clean

Usage

To use this implementation instead of the standard malloc:

LD_PRELOAD=./libmalloc.so ./your_program

Examples:

LD_PRELOAD=./libmalloc.so ls
LD_PRELOAD=./libmalloc.so ./tests/memoryfootprint

You can test the library with various programs by preloading it:

factor 10 20 30 40 50
cat Makefile
ip a
ls
ls -a
find /
tree /
clang --help
firefox
discord

Implementation Details

Memory Allocation Strategy

This allocator is based on a bucket system, where each bucket manages blocks of a fixed size.

Allocation Process (malloc)

1. Determines the nearest power-of-two block size.
2. Checks for an existing bucket with available space.
3. If none is found, creates a new bucket using mmap.
4. Allocates a free block from the selected bucket.

Freeing Memory (free)

1. Marks the block as free.
2. If the entire bucket is empty, it is munmapped to free system memory.

realloc Optimization

• If the requested size fits in the same bucket, reuse the block.
• If not, allocate a new block, copy data, and free the old one.

Testing

A set of precompiled test binaries is provided to validate your implementation.

Run tests using:

LD_PRELOAD=./libmalloc.so ./tests/<test_binary>

Provided Tests

Test Binary	Description
speed	Ensures the allocator runs within a fixed time limit.
memoryfootprint	Evaluates memory fragmentation and efficiency.
corruptionproof	Checks for metadata corruption resistance.

Example Test Runs

LD_PRELOAD=./libmalloc.so ./tests/speed; echo $?
# Expected output: 0 (success)

LD_PRELOAD=./libmalloc.so ./tests/memoryfootprint 512; echo $?
# Expected output: 50%+ memory efficiency (varies by implementation)

LD_PRELOAD=./libmalloc.so ./tests/corruptionproof; echo $?
# Expected output: 0 (success)

Debugging

Debugging a shared library requires special handling.

Using GDB with a linked binary

make debug
gdb ./your_program
(gdb) set env LD_LIBRARY_PATH=.
(gdb) run

Using GDB with LD_PRELOAD

make debug
gdb ls
(gdb) set exec-wrapper env 'LD_PRELOAD=./libmalloc.so'
(gdb) run

Contributing

Contributions are welcome! Feel free to open an issue or submit a pull request if you have ideas for improvements or new features.