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#define _POSIX_C_SOURCE 200809L
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>
#include "mapalloc.h"
#ifndef PAGESIZE
static size_t get_pagesize(void)
{
static size_t pagesize = 0;
if (pagesize == 0) {
pagesize = (size_t)sysconf(_SC_PAGESIZE);
}
return pagesize;
}
#define PAGESIZE get_pagesize()
#endif
struct bucket {
size_t used;
size_t allocated;
};
static void *page_alloc(size_t npages)
{
int fd = -1;
int prot = PROT_READ | PROT_WRITE;
int flags = MAP_PRIVATE;
#ifdef MAP_ANONYMOUS
flags = MAP_ANONYMOUS;
#else
fd = open("/dev/zero", O_RDONLY);
#endif
void *pages = mmap(NULL, npages * PAGESIZE, prot, flags, fd, 0);
if (fd != -1) {
close(fd);
}
return pages;
}
static void map_signal_action(int sig, siginfo_t *si, void *addr)
{
(void)sig;
fprintf(stderr, "error accessing %p\n", si->si_addr);
_exit(127 + SIGSEGV);
}
static void set_signal_handler(void)
{
struct sigaction sa = {
.sa_flags = SA_SIGINFO,
.sa_sigaction = map_signal_action,
};
sigemptyset(&sa.sa_mask);
sigaction(SIGSEGV, &sa, NULL);
}
static struct bucket *get_bucket(void *ptr, int allocate)
{
static uintptr_t *trie_top = NULL;
if (trie_top == NULL) {
trie_top = page_alloc(1);
memset(trie_top, 0, PAGESIZE);
}
set_signal_handler();
uintptr_t *trie = trie_top;
uintptr_t addr = (uintptr_t)ptr;
for (size_t i = 0; i < sizeof(addr); i++) {
uintptr_t next = (addr >> ((sizeof(addr) - i) * CHAR_BIT))
& UCHAR_MAX;
if (trie[next] == 0) {
if (allocate) {
uintptr_t *newtrie = page_alloc(1);
memset(newtrie, 0, PAGESIZE);
trie[next] = (uintptr_t) newtrie;
} else {
return NULL;
}
}
trie = (uintptr_t*)trie[next];
}
return trie ? (struct bucket *)trie : NULL;
}
void *map_calloc(size_t nelem, size_t elsize)
{
size_t n = nelem * elsize;
if (n < nelem || n < elsize) {
/* overflow */
return NULL;
}
void *ptr = map_malloc(n);
memset(ptr, 0, n);
return ptr;
}
void *map_malloc(size_t nbytes)
{
size_t pages = 2 + (nbytes / PAGESIZE);
if (nbytes % PAGESIZE != 0) {
pages++;
}
char *ptr = page_alloc(pages);
mprotect(ptr, PAGESIZE, PROT_NONE);
mprotect(ptr + ((pages - 1) * PAGESIZE), PAGESIZE, PROT_NONE);
struct bucket *b = get_bucket(ptr + PAGESIZE, 1);
b->used = nbytes;
b->allocated = pages * PAGESIZE;
return ptr + PAGESIZE;
}
void *map_realloc(void *ptr, size_t n)
{
if (ptr == NULL) {
return map_malloc(n);
}
struct bucket *b = get_bucket(ptr, 0);
if (b == NULL) {
fprintf(stderr, "attempt to realloc() invalid pointer %p\n", ptr);
abort();
}
if (n < (b->allocated - (PAGESIZE * 2))) {
b->used = n;
/* munmap() and mprotect() as necessary */
return ptr;
}
void *newptr = map_malloc(n);
if (newptr != NULL) {
memcpy(newptr, ptr, b->used);
map_free(ptr);
}
return newptr;
}
void map_free(void *ptr)
{
if (ptr == NULL) {
return;
}
struct bucket *b = get_bucket(ptr, 0);
if (b == NULL) {
fprintf(stderr, "attempt to free() invalid pointer %p\n", ptr);
abort();
}
char *base = ptr;
base -= PAGESIZE;
munmap(base, b->allocated);
/* clear bucket */
}
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