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101 rader
2.2 KiB
101 rader
2.2 KiB
/*
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* memlib.c - a module that simulates the memory system. Needed because it
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* allows us to interleave calls from the student's malloc package
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* with the system's malloc package in libc.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <assert.h>
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#include <unistd.h>
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#include <sys/mman.h>
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#include <string.h>
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#include <errno.h>
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#include "memlib.h"
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#include "config.h"
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/* private variables */
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static char *mem_start_brk; /* points to first byte of heap */
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static char *mem_brk; /* points to last byte of heap */
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static char *mem_max_addr; /* largest legal heap address */
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/*
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* mem_init - initialize the memory system model
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*/
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void mem_init(void)
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{
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/* allocate the storage we will use to model the available VM */
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if ((mem_start_brk = (char *)malloc(MAX_HEAP)) == NULL) {
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fprintf(stderr, "mem_init_vm: malloc error\n");
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exit(1);
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}
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mem_max_addr = mem_start_brk + MAX_HEAP; /* max legal heap address */
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mem_brk = mem_start_brk; /* heap is empty initially */
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}
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/*
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* mem_deinit - free the storage used by the memory system model
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*/
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void mem_deinit(void)
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{
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free(mem_start_brk);
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}
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/*
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* mem_reset_brk - reset the simulated brk pointer to make an empty heap
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*/
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void mem_reset_brk()
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{
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mem_brk = mem_start_brk;
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}
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/*
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* mem_sbrk - simple model of the sbrk function. Extends the heap
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* by incr bytes and returns the start address of the new area. In
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* this model, the heap cannot be shrunk.
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*/
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void *mem_sbrk(int incr)
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{
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char *old_brk = mem_brk;
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if ( (incr < 0) || ((mem_brk + incr) > mem_max_addr)) {
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errno = ENOMEM;
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fprintf(stderr, "ERROR: mem_sbrk failed. Ran out of memory...\n");
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return (void *)-1;
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}
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mem_brk += incr;
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return (void *)old_brk;
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}
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/*
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* mem_heap_lo - return address of the first heap byte
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*/
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void *mem_heap_lo()
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{
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return (void *)mem_start_brk;
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}
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/*
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* mem_heap_hi - return address of last heap byte
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*/
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void *mem_heap_hi()
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{
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return (void *)(mem_brk - 1);
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}
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/*
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* mem_heapsize() - returns the heap size in bytes
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*/
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size_t mem_heapsize()
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{
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return (size_t)(mem_brk - mem_start_brk);
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}
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/*
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* mem_pagesize() - returns the page size of the system
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*/
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size_t mem_pagesize()
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{
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return (size_t)getpagesize();
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}
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