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/*
* memlib.c - a module that simulates the memory system. Needed because it
* allows us to interleave calls from the student's malloc package
* with the system's malloc package in libc.
*/
#include "memlib.h"
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#define MAX_HEAP (100 * (1 << 20)) /* 100 MB */
/* private variables */
static uint8_t *heap;
static uint8_t *mem_brk;
/*
* mem_init - initialize the memory system model
*/
void mem_init() {
heap = mmap((void *) 0x800000000, /* suggested start*/
MAX_HEAP, /* length */
PROT_READ | PROT_WRITE, /* heap can be read or written */
MAP_PRIVATE | MAP_ANONYMOUS, /* initialize region with zeros */
-1, /* fd (unused) */
0 /* offset (unused) */
);
/* Heap is initially empty. */
mem_reset_brk(true);
}
/*
* mem_deinit - free the storage used by the memory system model
*/
void mem_deinit() {
munmap(heap, MAX_HEAP);
}
/*
* mem_reset_brk - reset the simulated brk pointer to make an empty heap
*/
void mem_reset_brk(bool clear) {
mem_brk = heap;
/* Fill heap with garbage since it is uninitialized. */
if (clear) {
memset(heap, 0xCC, MAX_HEAP);
}
}
/*
* mem_sbrk - simple model of the sbrk function. Extends the heap
* by incr bytes and returns the start address of the new area. In
* this model, the heap cannot be shrunk.
*/
void *mem_sbrk(ssize_t incr) {
void *old_brk = mem_brk;
if (incr < 0 || mem_brk + incr > heap + MAX_HEAP) {
errno = ENOMEM;
fprintf(stderr, "ERROR: mem_sbrk failed. Ran out of memory...\n");
return (void *) -1;
}
mem_brk += incr;
return old_brk;
}
/*
* mem_heap_lo - return address of the first heap byte
*/
void *mem_heap_lo() {
return heap;
}
/*
* mem_heap_hi - return address of last heap byte
*/
void *mem_heap_hi() {
return mem_brk - 1;
}
/*
* mem_heapsize() - returns the heap size in bytes
*/
size_t mem_heapsize() {
return mem_brk - heap;
}