https://github.com/ritwickdey/malloc-impl-demo

Minimal implementation of malloc and free for demo purposes.
https://github.com/ritwickdey/malloc-impl-demo

demo free knowlage-share malloc

Last synced: about 1 month ago
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Minimal implementation of malloc and free for demo purposes.

• Host: GitHub
• URL: https://github.com/ritwickdey/malloc-impl-demo
• Owner: ritwickdey
• License: mit
• Created: 2022-03-20T15:03:06.000Z (almost 3 years ago)
• Default Branch: master
• Last Pushed: 2022-03-21T07:16:20.000Z (almost 3 years ago)
• Last Synced: 2024-11-11T15:24:46.671Z (3 months ago)
• Topics: demo, free, knowlage-share, malloc
• Language: C
• Homepage:
• Size: 672 KB
• Stars: 10
• Watchers: 3
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
Minimal implementation of `malloc` and `free` using `sbrk()` and `brk()` system calls. 

### Context:

How does a process *actually* request the kernel to allocate/deallocate memory blocks in runtime?

Whenever we create an object or list, we allocate memory in heap. Unlike `stack`, memory allocation in `heap` happens in runtime. No matter what programming language you choose, the fundamentals remain the same. 

In Clang, there is `malloc()` to create memory in heap and `free()` to release the memory. If you don't know `Clang`, you can relate `malloc()` call as your creating object from Class.

But there are no `free()` equivalent functions available in other high level-programming languages as they have automatic garbage collection. Probably garbage collector has some function like `free()`.

But `malloc()` and `free()` is library (`glibc`) functions, which means anyone can implement those function or tweak those function. Then the question is how `malloc()` or `free()` allocate or deallocate memory. 

There is a few `system call` available to do that. `brk`, `sbrk` and `mmap`, `munmap`. Please check the man page to know more about the functions.

Here I've tried to implement `malloc` and `free` using `brk`, `sbrk` system calls.

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### Local setup

```

> cd 

> mkdir bin obj

> make build

> ./bin/mem_test

```

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### Gist

!! Try to read **only** the comments.

`my_malloc()` implementation using `brk` and `sbrk`.



`my_free()` implementation using `brk` and `sbrk`.



### Reference:

- https://blog.holbertonschool.com/hack-the-virtual-memory-malloc-the-heap-the-program-break/

- The Linux Programming Interface by Michael Kerrisk

- Man page https://man7.org/linux/man-pages/man2/sbrk.2.html

- https://stackoverflow.com/questions/6988487/what-does-the-brk-system-call-do (https://stackoverflow.com/a/31082353)

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