Custom Heap Allocator in Netwide Assembly

Warning

This custom heap allocator implementation is for educational or experimental purposes only. It is NOT suitable yet for production use due to the following limitations:

1. Limited Error Handling: This implementation may lack robust error-checking mechanisms and could fail unpredictably with large or unexpected allocations.

2. No Thread Safety: This allocator is not designed to handle concurrent memory allocations from multiple threads. Use in a multi-threaded environment could lead to data races or crashes.

3. No Memory Protection: this implementation does not guarantee that freed memory cannot be accessed, which may lead to undefined behavior.

Usage

Allocation

To allocate memory, use the malloc function:

mov     rdi, 64          ; Size in bytes
call    malloc           ; Allocates 64 bytes and returns pointer in RAX

cmp     rax, 0
jl      .error           ; make sure it didn't fail 

Deallocation

To free allocated memory, use the free function:

mov     rdi, rax         ; Address of the memory chunk to free
call    free             ; Deallocates memory at the given address

cmp     rax, 0
jl      .error           ; make sure it didn't fail 

Other functions

To allocate memory and initialise all bytes to zero, use the calloc function:

mov     rdi, 10          ; number of elements
mov     rsi, 64          ; size of each element
call    calloc           ; Allocate 10 elements of 64 bytes and initialise to 0 

cmp     rax, 0
jl      .error           ; make sure it didn't fail 

Example

section .text
    global _start

    ; include .inc files
    %include "utils.inc"
    %include "malloc.inc"
    %include "free.inc"
    %include "memset.inc"
    %include "mmap.inc"

_start:
    ; allocate memory
    mov     rdi, 64
    call    malloc

    cmp     rax, 0
    jl      .error

    mov     rbx, rax      ; Store allocated pointer

    ; write data to the memory
    mov     qword [rbx], 0x1234

    ; free allocated memory
    mov     rdi, rbx
    call    free

    cmp     rax, 0
    jl      .error

    ; exit
    mov     rax, SYS_EXIT
    mov     rdi, SUCCESS_CODE
    syscall

.error:
    mov     rax, SYS_EXIT
    mov     rdi, FAILURE_CODE
    syscall