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/* This should look a lot like 15-213 support code.
* Guess what...
*/
/* memlib.c - functions for modeling the memory system */
/* $begin memlib */
#include <stddef.h>
#include <stdio.h>
#include <syscall.h>
/* #define PAGE_SIZE 0x00001000 */
/* #define PAGE_ALIGN_MASK 0xFFFFF000 */
#define PAGE_ALIGN_MASK ((unsigned int) ~((unsigned int) (PAGE_SIZE-1)))
#ifndef NULL
#define NULL 0
#endif
/* private global variables */
static char *mem_max_addr; /* max virtual address for the heap */
static char *mem_brkp; /* Simulated brk pointer */
static char *mem_alloctop; /* Maximum allocated address */
extern void *_end; /* The end of the ELF binary address space */
/*
* mem_init - initializes the memory system model
*/
void mem_init(int max_heap_addr)
{
/* The max address for the heap. */
mem_max_addr = (char*)max_heap_addr;
mem_brkp = (char*)&_end + PAGE_SIZE;
mem_brkp = (char*)((int)mem_brkp & PAGE_ALIGN_MASK);
while (new_pages(mem_brkp, PAGE_SIZE))
mem_brkp += PAGE_SIZE;
mem_alloctop = mem_brkp + PAGE_SIZE;
}
/*
* mem_sbrk - simply uses the 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(int incr)
{
char *old_brk = mem_brkp;
/* Error check the request. */
if ( (incr < 0) || ((old_brk + incr) > mem_max_addr)) {
return (void *)NULL;
}
if (old_brk + incr > mem_alloctop) {
int allocincr = old_brk + incr - mem_alloctop;
allocincr += PAGE_SIZE - 1;
allocincr &= PAGE_ALIGN_MASK;
/* Issue a SBRK for more memory. */
if (new_pages((void*)mem_alloctop, allocincr)) {
return (void *)NULL;
}
mem_alloctop += allocincr;
}
mem_brkp += incr;
return (void *)old_brk;
}
/* $end memlib */
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