malloc

Implementation of malloc library (malloc, free and a few other functions) that can be used in regular applications like vim, ls or firefox (just tell the dynamic linker to use it instead of glibc).

Description

This memory allocator uses double-linked lists to keep track of free blocks. Finding a block is a simple first-fit algorithm. When there is no free block (or not big enough free block), it asks kernel for some new pages (using mmap) and creates a new block chunk. Empty chunks are unmmaped.

Implemented funtions

There are 5 main functions in src/malloc.c:

void *foo_malloc(size_t size);
void *foo_calloc(size_t count, size_t size);
void *foo_realloc(void *ptr, size_t size);
int foo_posix_memalign(void **memptr, size_t alignment, size_t size);
void foo_free(void *ptr);

and they are conforming to POSIX and C standards.

Functions are prefixed with foo_ to prevent interference with glibc during development and testing. In src/malloc.h you will find macros

#define DELETE_FOO 1

#if DELETE_FOO
    #define foo_malloc malloc
    #define foo_calloc calloc
    #define foo_realloc realloc
    #define foo_posix_memalign posix_memalign
    #define foo_free free
#endif

that delete this prefix.

How to use it in regular app

For example, to run vim that uses this malloc implementation, type:

$ make

It will create build/malloc.so shared library. Now you have to simply run vim with LD_PRELOAD environment variable set, that will tell the dynamic linker that this shared ELF should be loaded before all others.

$ LD_PRELOAD=$PWD/build/malloc.so vim

Feel free to try it on ls, xeyes, gnome-calculator, firefox or nautilus.

Tests

In tests folder you will find two tests:

• functional.c that checks some randomly interleaved scenario (as well as memory integrity after each action),
• standards.c that checks conformance to standards, e.g. whether calloc sets memory to zero or whether posix_memalign returns EINVAL when given bad alignment etc.

Tests are written in minunit, a "minimal unit testing framework for C". Running them is as simple as:

$ make test