Segmentation error in programm

[nigga-man]

I'm a complete noob and I need help! I like everything written correctly, here's the code:

#include <stdio.h>
#include "iwlib.h"

int set_essid(int    skfd, char ifname[], char arg[], int count);

int main(int argc, char *argv[])
{
  int skfd;
  if((skfd = iw_sockets_open()) < 0)
  {
    perror("socket");
    exit(-1);
  }
  
  if(argc != 3) {
    printf("USING: %s [FACE] [essid]\n", argv[0]);
    goto quit;
  }
  
  if( set_essid(skfd, argv[2], argv[3], 0) == 0 ) {
    printf("OK!\n");
  }
  else {
    printf("ERROR!\n");
    perror("iw_set_ext");
  }
  
  quit:
  iw_sockets_close(skfd);
  return 0;
}

int set_essid(int    skfd, char ifname[], char arg[], int count)
{
  struct iwreq wrq;
  char essid[IW_ESSID_MAX_SIZE + 1];
  int we_kernel_version;
  
  
  wrq.u.essid.flags = 1;
  strcpy(essid, arg);
  
  we_kernel_version = iw_get_kernel_we_version();
  
  wrq.u.essid.pointer = (caddr_t) essid;
  wrq.u.essid.length = strlen(essid);
  if(we_kernel_version < 21)
    wrq.u.essid.length++;

  if(iw_set_ext(skfd, ifname, SIOCSIWESSID, &wrq) < 0)
    return(-1);
  
  return 0;
}

I compiled this way

gcc libiw.so.29 main.c -lm -Wall

At startup gives an error:

user $ ./a.out wifi d
Segmentation error (the memory stack is flushed to disk)

Help me!!!!

[Salem]

This is where learning how to use a debugger comes in handy.

$ gcc -g foo.c -liw
$ ./a.out wifi d
Segmentation fault (core dumped)
$ gdb -q ./a.out
Reading symbols from ./a.out...done.
(gdb) run wifi d
Starting program: /home/salem/a.out wifi d

Program received signal SIGSEGV, Segmentation fault.
__strcpy_sse2_unaligned () at ../sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S:296
296	../sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S: No such file or directory.
(gdb) bt
#0  __strcpy_sse2_unaligned () at ../sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S:296
#1  0x0000000000400af1 in set_essid (skfd=3, ifname=0x7fffffffe265 "d", arg=0x0, count=0) at foo.c:41
#2  0x0000000000400a75 in main (argc=3, argv=0x7fffffffde98) at foo.c:20
(gdb) frame 1
#1  0x0000000000400af1 in set_essid (skfd=3, ifname=0x7fffffffe265 "d", arg=0x0, count=0) at foo.c:41
41	  strcpy(essid, arg);
(gdb) frame 2
#2  0x0000000000400a75 in main (argc=3, argv=0x7fffffffde98) at foo.c:20
20	  if( set_essid(skfd, argv[2], argv[3], 0) == 0 ) {
(gdb) print argv[0]
$1 = 0x7fffffffe23d "/home/salem/a.out"
(gdb) print argv[1]
$2 = 0x7fffffffe260 "wifi"
(gdb) print argv[2]
$3 = 0x7fffffffe265 "d"

It looks like you mis-counted your arguments.

[userxbw]

remember you're working off a zero base .. 0 = program name 1 = next item 2 = next item check with argc for length on cli

int main(int argc, char **argv)
{

if ( argc != 2  )
{
    printf("error_message"\n);
    exit(1);
}
..........

return 0;
}

[ordak]

Please do not use goto at all.

[nigga-man]

This is where learning how to use a debugger comes in handy.

$ gcc -g foo.c -liw
$ ./a.out wifi d
Segmentation fault (core dumped)
$ gdb -q ./a.out
Reading symbols from ./a.out...done.
(gdb) run wifi d
Starting program: /home/salem/a.out wifi d

Program received signal SIGSEGV, Segmentation fault.
__strcpy_sse2_unaligned () at ../sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S:296
296    ../sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S: No such file or directory.
(gdb) bt
#0  __strcpy_sse2_unaligned () at ../sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S:296
#1  0x0000000000400af1 in set_essid (skfd=3, ifname=0x7fffffffe265 "d", arg=0x0, count=0) at foo.c:41
#2  0x0000000000400a75 in main (argc=3, argv=0x7fffffffde98) at foo.c:20
(gdb) frame 1
#1  0x0000000000400af1 in set_essid (skfd=3, ifname=0x7fffffffe265 "d", arg=0x0, count=0) at foo.c:41
41      strcpy(essid, arg);
(gdb) frame 2
#2  0x0000000000400a75 in main (argc=3, argv=0x7fffffffde98) at foo.c:20
20      if( set_essid(skfd, argv[2], argv[3], 0) == 0 ) {
(gdb) print argv[0]
$1 = 0x7fffffffe23d "/home/salem/a.out"
(gdb) print argv[1]
$2 = 0x7fffffffe260 "wifi"
(gdb) print argv[2]
$3 = 0x7fffffffe265 "d"

It looks like you mis-counted your arguments.

Ah that's the problem, the whole program works!