Re: sendto generates SIGSEGV

[Matti Aarnio <matti.aarnio@zmailer.org>]

On Sun, Jul 29, 2001 at 11:27:29PM +0200, Oliver Kowalke wrote:
> From:	oliver.kowalke@t-online.de (Oliver Kowalke)
> To:	linux-kernel@vger.kernel.org
> Subject: sendto generates SIGSEGV
> Date:	Sun, 29 Jul 2001 23:27:29 +0200

  Two hours ago you asked this very same question at the  linux-net -list.
  At how many lists you are asking this ?

> Hi,
> 
> I've written an c++ class which wrappes a socket.. With function writen() 
> you can write to an TCP and UDP socket ( TCP : pointer to stuct sockaddr == 
> NULL; UDP :  pointer to struct sockaddr != NULL). If I use this function 
> with TCP sockets all works. If I call this function for an UDP socket it 
> generates an SIGSEGV signal.
> What is wrong?

    You are presenting incomplete source, and worse, incomplete
  debug trace.   Furthermore, this really does not look like KERNEL
  problem, which makes it  Out-of-Topic  issue at these lists.

  From certain signature features in the very scant debug data, I would
  venture to think that you are running it at Solaris, and debugging
  it there.

  Do yourself a favour and learn to use debuggers, and compile for
  debugging.   ``Backtrace'' or ``where'' (or whatever the debugger
  of your choice calls it) is your friend in most cases.


  Syscall trace may give you also some clues in some cases.
  At Solaris see: 'man truss'.  At Linux see: 'man strace'.

  If you can show  strace  output with SIGSEGV during a network syscall,
  now THAT would be most appropriate at the   linux-net   list.

> with regards,
> Oliver

    /Matti Aarnio

> ssize_t writen( const void * vptr, size_t n, struct sockaddr * to)
> {
>         size_t          nleft = n;
>         ssize_t         nwritten;
>         const char      *ptr = static_cast< const char * >( vptr);
>         
>         struct sigaction new_sa;
>         struct sigaction old_sa;
>         
>         new_sa.sa_handler = SIG_IGN;
>         ::sigemptyset( & new_sa.sa_mask);
>         new_sa.sa_flags = 0;
>         ::sigaction( SIGPIPE, & new_sa, & old_sa);              
> 
>         while ( nleft > 0)
>         {
> 
>                 if ( ( nwritten = ::sendto( m_handle, ptr, nleft, 0, to, sizeof * to) )<=0)
>                 {
>                         if ( errno == EINTR)
>                                 nwritten = 0;   // and call sendto() again
>                         else if ( errno == EPIPE)
>                         {
>                                 ::sigaction( SIGPIPE, & old_sa, 0);
> 
>                                 return -1;              // write to sock with no readers (peer has the sock closed)
> 
>                         }
>                         else
>                         {
>                                 ::sigaction( SIGPIPE, & old_sa, 0);
>                                 throw; // error
>                         }
>                 }
> 
>                 nleft -= nwritten;
>                 ptr   += nwritten;
>         }
>         ::sigaction( SIGPIPE, & old_sa, 0);     // set to its previous action
> 
>         return n;
> }
> 
> here the output of the generated core file:
> 
> Core was generated by 'lt-ogx 192.168.1.3 10000'.
> Program terminated with signal 11, Segmentation fault.
> rw_common (): write: Success.
> warning: unable to get global thread event mask
> [New Thread 1024 (LWP 32350)]
> rw_common (): write: Success.
> warning: stop_or_attach_thread: generic error
> #0 0x0 in ?? ()