Re: [XenAccess-devel] Segmentation fault when calling the same function twice

[Daniele S. <da...@ya...>]

> 
> Have you been able to reproduce this problem without
> the python  
> ctypes library?
 
I've been trying these days to locate the problem: I
don't know very well how to use ctypes. But I've been
able to reproduce the same problem in C; the file is
process-data.c: again, the "main" has been renamed to
"process-data" and I've removed all the printf
statements:

-------------------------process-data.c-------------------------

#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/mman.h>
#include <stdio.h>
#include "../xenaccess.h"
#include "../xa_private.h"

int process_data (int argc, char **argv)
{
    xa_instance_t xai;
    xa_linux_taskaddr_t taskaddr;
    unsigned char *memory = NULL;
    uint32_t offset = 0;

    /* this is the domain ID that we are looking at */
    uint32_t dom = atoi(argv[1]);

    /* This is the pid that we are looking at, passed
as
       an argument on the command line. */
    int pid = atoi(argv[2]);

    /* initialize the xen access library */
    if (xa_init(dom, &xai) == XA_FAILURE){
        perror("failed to init XenAccess library");
        goto error_exit;
    }

    /* get the relavent addresses for this process */
    if (xa_linux_get_taskaddr(&xai, pid, &taskaddr) ==
XA_FAILURE){
        perror("failed to get task addresses");
        goto error_exit;
    }

    /* grab the memory at the start of the code
segment
       for this process and print it out */
    memory = xa_access_user_virtual_address(
                &xai, taskaddr.start_code, &offset,
pid);
    if (NULL == memory){
        perror("failed to map memory");
        goto error_exit;
    }

error_exit:

    /* cleanup any memory associated with the
XenAccess instance */
    xa_destroy(&xai);

    /* sanity check to unmap shared pages */
    if (memory) munmap(memory, XA_PAGE_SIZE);

    return 0;
}

int main (int argc, char **argv)
{
  int i;
  for(i=0; i<100; i++)
    {
      printf("%d ", i);
      process_data(argc, argv);
    }
  return 0;
}

-------------------------------------------------------------------
[root@dhcp12 example]# xm list
Name                              ID Mem(MiB) VCPUs
State  Time(s)
Debian1                            1       64     1
-b----    12.7
Domain-0                           0      419     1
r-----    74.4

[root@dhcp12 example]# ./run ./process-data 1 1
Entity: line 1: parser error : Start tag expected, '<'
not found
^
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
ERROR: could not parse xml data for domain id 1
*** glibc detected *** ./process-data: double free or
corruption (!prev): 0x08ed3d30 ***
======= Backtrace: =========
/lib/libc.so.6[0xdd0d0a]
/lib/libc.so.6(__libc_free+0x70)[0xdd3f48]
../libxenaccess.so(linux_get_kernel_name+0x127)[0xd6e287]
../libxenaccess.so(linux_predict_sysmap_name+0x1f)[0xd6e34f]
../libxenaccess.so(linux_system_map_symbol_to_address+0x28)[0xd6d7b8]
../libxenaccess.so(linux_access_kernel_symbol+0x75)[0xd6dfd5]
../libxenaccess.so(xa_access_kernel_symbol+0x34)[0xd6ca14]
../libxenaccess.so(helper_init+0xfb)[0xd6c88b]
../libxenaccess.so(xa_init+0x42)[0xd6c922]
./process-data[0x80486a2]
./process-data[0x804878f]
/lib/libc.so.6(__libc_start_main+0xc6)[0xd8670e]
./process-data[0x80485a1]
.....


The problem is that sometime everything just works
fine!
I hope that can help you!
Thanks!!!




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