Hi,
I try a simple C program for check mmap() function.
Is it possible for Valgrind notify if a memory region has a mmap() but
not the munmap() ??
The program's code is:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#define FILEPATH "test.txt"
#define NUMINTS (1000)
#define FILESIZE (NUMINTS * sizeof(int))
int main(int argc, char *argv[])
{
int i;
int fd;
int result;
int *map; /* mmapped array of int's */
/* Open a file for writing.
* - Creating the file if it doesn't exist.
* - Truncating it to 0 size if it already exists. (not really
needed)
*
* Note: "O_WRONLY" mode is not sufficient when mmaping.
*/
fd = open(FILEPATH, O_RDWR | O_CREAT | O_TRUNC, (mode_t)0600);
if (fd == -1) {
perror("Error opening file for writing");
exit(EXIT_FAILURE);
}
/* Stretch the file size to the size of the (mmapped) array of ints */
result = lseek(fd, FILESIZE-1, SEEK_SET);
if (result == -1) {
close(fd);
perror("Error calling lseek() to 'stretch' the file");
exit(EXIT_FAILURE);
}
/* Something needs to be written at the end of the file to
* have the file actually have the new size.
* Just writing an empty string at the current file position
will do.
*
* Note:
* - The current position in the file is at the end of the
stretched
* file due to the call to lseek().
* - An empty string is actually a single '\0' character, so a
zero-byte
* will be written at the last byte of the file.
*/
result = write(fd, "", 1);
if (result != 1) {
close(fd);
perror("Error writing last byte of the file");
exit(EXIT_FAILURE);
}
/* Now the file is ready to be mmapped. */
map = (int *) mmap(0, FILESIZE, PROT_READ | PROT_WRITE,
MAP_SHARED, fd, 0);
if (map == MAP_FAILED) {
close(fd);
perror("Error mmapping the file");
exit(EXIT_FAILURE);
}
/* Now write int's to the file as if it were memory (an array
of ints). */
for (i = 1; i <=NUMINTS; ++i) {
map[i] = 2 * i;
}
/* Don't forget to free the mmapped memory */
if (munmap(map, FILESIZE) == -1) {
perror("Error un-mmapping the file");
}
/* Un-mmaping doesn't close the file, so we still need to do
that. */
close(fd);
return 0;
}
Thanks.
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