lkml.org 
[lkml]   [2003]   [Nov]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Subjectmmap and MAP_FIXED question
Date
Hi,

I currently do not have subscribed to LKML, so please CC to my address when
answering. I will browse the archive, but on a not so regular basis.

I came across a strange behavior of mmap using the ACE library. After some
discussion on the ace-users mailing list
(http://groups.yahoo.com/group/ace-users/message/36897) I'd like to post this
question here in the hope that anyone knows more about this.

The problem basically is that a program doing a mmap call with the MAP_FIXED
flag set crashes just by unmapping and mapping of an extended (larger) memory
area. Note it crashes although it never touches (writes) to the memory it
maps.

Attached is a C file that if compiled and run on a 2.4.x Kernel crashes with a
segmentation fault. If called with any argument it uses a (delta) value to
increase the map size, so it crashes after 21 iterations on my computer.
My kernel version is:
$ cat /proc/version
Linux version 2.4.20-18.9.acpi.4 (dsanta@ltspc67.epfl.ch) (gcc version 3.2.2
20030222 (Red Hat Linux 3.2.2-5)) #1 Wed Jul 2 14:54:57 CEST 2003

If anyone knows why the program crashes instead of just failing with some
error code, please let me know.

The attached program is a slightly modified version I got from an ACE
developer
> Here's my test program. It fails under all machines that I have tested.
> Maybe you can post it to Linux Kernel and ask what is broken and tell me if
> you get any answer.

Lothar
--
Lothar Werzinger Dipl.-Ing. Univ.
framework & platform architect
Xcerla Corporation
275 Tennant Avenue, Suite 202
Morgan Hill, Ca 95037
email: lothar@xcerla.com
phone: +1-408-776-9018#include <sys/mman.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

int main(int argc, char ** argv)
{
int fd = 0;
int pagesize = 0;
unsigned int delta = 0;
int retval = 0;
size_t count = 0;
size_t size = 0;
char* addr = 0;

pagesize = getpagesize();

srand(time(0));
delta = rand() % pagesize;
if (argc > 1)
delta = 0xf96;

fprintf (stderr, "pagesize %d\n", pagesize);
fprintf (stderr, "using delta %06d, %06x\n", delta, delta);


fd = open ("/tmp/MemMapTest1.data", O_RDWR|O_CREAT);
if (fd == -1)
{
fprintf (stderr, "Unable to create file: %s\n", strerror (errno));
exit (1);
}
if (unlink ("/tmp/MemMapTest1.data") == -1)
{
fprintf (stderr, "Unable to unlink file: %s\n", strerror (errno));
exit (1);
}

retval = ftruncate (fd, delta);
if (retval == -1)
{
fprintf (stderr, "Unable to resize file: %s\n", strerror (errno));
exit (1);
}

size = delta;
addr = (char*) mmap (0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (addr == MAP_FAILED)
{
fprintf (stderr, "Unable to map file: %s\n", strerror (errno));
exit (1);
}

fprintf (stderr, "%03d address: %p, size: %06d, %06x, new size: %06d, %06x\n",
count, addr, size, size, size + delta, size + delta);

while (count < 500)
{
if (munmap(addr, size) == -1)
{
fprintf (stderr, "Unable to unmap file: %s\n", strerror (errno));
exit (1);
}

size += delta;
retval = ftruncate (fd, size);
if (retval == -1)
{
fprintf (stderr, "Unable to resize file: %s\n", strerror (errno));
exit (1);
}
addr = (char*) mmap (addr, size, PROT_READ|PROT_WRITE,
MAP_SHARED|MAP_FIXED, fd, 0);
if (addr == MAP_FAILED)
{
fprintf (stderr, "Unable to map file: %s\n", strerror (errno));
exit (1);
}

++count;
fprintf (stderr, "%03d address: %p, size: %06d, %06x, new size: %06d, %06x\n",
count, addr, size, size, size + delta, size + delta);
}
fprintf (stderr, "%03d exited loop\n", count);
return 0;
}
\
 
 \ /
  Last update: 2005-03-22 13:58    [W:0.022 / U:0.564 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site