[Python-bugs-list] [ python-Bugs-448351 ] coredump in selectmodule.c on Solaris 8

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Bugs item #448351, was opened at 2001-08-06 01:23
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Category: Extension Modules
Group: Platform-specific
Status: Open
Resolution: Fixed
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
>Assigned to: Barry Warsaw (bwarsaw)
Summary: coredump in selectmodule.c on Solaris 8

Initial Comment:
I get coredump if I run a small script with Python 2.0
on Solaris 8, compiled with Sun CC Forte 6.1 compiler
(64 bits). I suggest to run it more than once to
produce the error. Purify showed me that there are
reading and writings outside the stack boundary.  

The interesting part of the source:

Modules/selectmodule.c
.
.
static PyObject *
select_select(PyObject *self, PyObject *args)
{
#ifdef MS_WINDOWS
        /* This would be an awful lot of stack space on
Windows! */
        pylist *rfd2obj, *wfd2obj, *efd2obj;
#else
        pylist rfd2obj[FD_SETSIZE + 3];
        pylist wfd2obj[FD_SETSIZE + 3];
        pylist efd2obj[FD_SETSIZE + 3];
#endif
.
.
.
}

In our environment FD_SETSIZE is 65536 as defined in
sys/select.h (see
below). The allocated stack space in select_select is
3*sizeof(rfd2obj)*(FD_SETSIZE+3). It is more than
3Mbytes. The difference between the addresses of the
same variable in two
seperate threads is about 2Mbytes. Lets suppose char
*p1 = (char *)rfd2obj
in thread N and char *p2 = (char *)rfd2obj in thread N
+ 1, abs(p1-p2)
is about 2MB (dbx showed this). The stack is
overwritten between the threads. Is it possible that
the stack size is limited to 2 Mbytes per thread? We
fixed it as solved on Windows allocating these
variables on the heap.

Select.h from Solaris 8.

/usr/include/sys/select.h:
.
.
#ifndef FD_SETSIZE
#ifdef _LP64
#define FD_SETSIZE      65536
#else
#define FD_SETSIZE      1024
#endif  /* _LP64 */
.
.

----------------------------------------------------------------------

>Comment By: Tim Peters (tim_one)
Date: 2001-08-16 14:58

Message:
Logged In: YES 
user_id=31435

Back to Barry for re-testing on Linux:  I checked in 
another version that refuses to add 3 to FD_SETSIZE 
anymore.  Fortune favors the bold.

----------------------------------------------------------------------

Comment By: Barry Warsaw (bwarsaw)
Date: 2001-08-16 09:53

Message:
Logged In: YES 
user_id=12800

I've just checked in a minimal patch, taking the easy way
out (i.e. testing for FD_SETSIZE > 1024).  This subtly
changes the behavior on Windows (where Tim says the value is
now 512) since Windows won't normally take the
allocate-on-heap path now.  

selectmodule.c 2.54 has the change.

The changes pass on Linux both for normal, small FD_SETSIZEs
and for artificially cranked FD_SETSIZEs.  Assigning back to
Tim for verification on Windows.

----------------------------------------------------------------------

Comment By: Tim Peters (tim_one)
Date: 2001-08-06 13:52

Message:
Logged In: YES 
user_id=31435

Reassigned to Barry.  I may a good choice to write the 
code, but not to test it (I know zilch about sockets, and 
can't provoke the problem on Windows anyway).

----------------------------------------------------------------------

Comment By: Guido van Rossum (gvanrossum)
Date: 2001-08-06 05:36

Message:
Logged In: YES 
user_id=6380

Dear Anonymous,

a quick workaround is to change the three #ifdef MS_WINDOWS
in selectmodule.c into #if FD_SETSIZE > 1024.

A better idea is currently being discussed on python-dev.


----------------------------------------------------------------------

Comment By: Nobody/Anonymous (nobody)
Date: 2001-08-06 01:31

Message:
Logged In: NO 

The attachment missed, this is the mentioned script:

import threading
import telnetlib

def telnetToHost():
    
        hostname = "my_hostname"
        username = "user_name"
        password = "password"
        
        tn = telnetlib.Telnet(hostname)
        tn.read_until("login: ")
        tn.write(username + '\n')
        tn.read_until("Password: ")
        tn.write(password + '\n')

class MyThread(threading.Thread):
        
        def run(self):
                print "ThreadID", self.cnt, "started"
                telnetToHost()
                print "ThreadID", self.cnt, "finished"

for i in range(0,4):
        m = MyThread()
        m.cnt = i
        m.start()

----------------------------------------------------------------------

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