Basic arena allocator(incomplete)

.c

#include <sys/mman.h>
#include <stdint.h>
#include <stddef.h>
#include <sanitizer/asan_interface.h>
#include "./stdint.h"

typedef struct
{
    u8  *arena_start_pos;
    size_t size;//total bytes allocated for the arena
    size_t offset;//bytes used up
} Arena, *ptr_arena;

#define KB(T) ((T)*1024)
#define MB(T) ((T)*1024*1024)
#define GB(T) ((T)*1024*1024*1024)

//#define arena_push_array(arena, type, count) (type *)arena_push((arena), (sizeof(type)*count))
#define arena_array_push_and_zero(arena, type, count) (type *)arena_push_and_zero((arena), (sizeof(type)*count))
#define arena_struct_push(arena, type) (type *)arena_push((arena), sizeof(type)*1 )
#define arena_struct_push_and_zero(arena, type) (type *)arena_push_and_zero((arena), sizeof(type)*1 )
#define arena_array_of_structs_push(arena, type, count) (type *)arena_push((arena), (sizeof(type)*count))

#define arena_init(name) Arena name = {0};

void arena_allocate(Arena *arena, size_t size)
{
    arena->arena_start_pos = (u8 *)mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    arena->size = size;
}

void *arena_push(Arena *arena, size_t size)
{
    void *ptr_temp = arena->arena_start_pos + arena->offset;
    arena->offset += size;
    return ptr_temp;
}

#define vector(T) struct { T *data; ptrdiff_t length, capacity; }

#define arena_array_init_and_push(arena, type, num_elements) \
    { \
        .data = (type *)arena_push((arena), sizeof(type)*(num_elements)), \
        .length = 0, \
        .capacity = (num_elements) \
    }