mmap-test

.gitignore

*swp
*swo
*.o
mmtest

Makefile

%.o:%.c
	gcc -c -g -m32 -o $@ $<

mmtest: mmtest.o
	gcc -g -m32 -o $@ $^

mmtest.o: mmtest.c

.PHONY: clean
	clean:
	-@rm *.o main &> /dev/null

mmtest.c

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int pmap() {
    char buf[4096];
    snprintf(buf, 4096, "vmmap %d", getpid()); // darwin version
    // snprintf(buf, 4096, "pmap %d", getpid()); // linux version
    system(buf);
}

int main(int argc, char **argv) {
    size_t LEN = 4096;
    void *addr = NULL;
    void *addr2 = NULL;
    int err = 0;
    int *arr = NULL;
    int i = 0;
    addr = mmap( NULL, LEN, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    fprintf(stderr, "mmap addr %p\n", addr);
    if (addr == MAP_FAILED) {
      int err = errno;
      char *msg = NULL;
      errno = 0;
      msg = strerror(err);
      fprintf(stderr, "mmap error %s\n", msg);
      return -1;
    }
    arr = (int *)addr;
    for (i = 0; i < LEN/4; i++) {
      arr[i] = i;
    }
    fprintf(stderr, "expected mmap addr2 %p\n", addr + LEN);
    addr2 = mmap(addr + LEN, LEN, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED | MAP_FIXED, -1, 0);
    if (addr2 == MAP_FAILED) {
      int err = errno;
      char *msg = NULL;
      errno = 0;
      msg = strerror(err);
      fprintf(stderr, "mmap error %s\n", msg);
      return -1;
    }
    fprintf(stderr, "mmap addr2 %p\n", addr2);
    pmap();
    for (i = LEN/4; i < (LEN*2)/4; i++) {
      arr[i] = 0xff;
    }
    for (i = 0; i < (LEN*2)/4; i++) {
      fprintf(stdout, "arr %d %d\n", i, arr[i]);
    }
    err = munmap(addr, LEN * 2);
    if (err != 0) {
      int err = errno;
      char *msg = NULL;
      errno = 0;
      msg = strerror(err);
      fprintf(stderr, "munmap error %s\n", msg);
      return -1;
    }
    pmap();
    return 0;
}