[Python-bugs-list] [ python-Bugs-462783 ] mmap bus error on linux

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Bugs item #462783, was opened at 2001-09-19 03:31
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Category: Extension Modules
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Andrew Dalke (dalke)
>Assigned to: Neal Norwitz (nnorwitz)
Summary: mmap bus error on linux

Initial Comment:
Not using the mmap module correctly can cause a
bus error under Linux.  This is a DEC, err, Compaq,
err, HP Alpha.

Here's a reproducible.  The problem appears to
be trying to mmap past the end of the file,
since putting in a "seek(0)" at the indicated
spot fixes things.


[dalke@pw600a src]$ ./python
Python 2.2a3+ (#6, Sep 17 2001, 05:05:24)
[GCC egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)] 
on linux2
Type "help", "copyright", "credits" or "license" for 
more information.
>>> file = open("test.dat", "w+")
>>> file.write("12345")
>>> import mmap
>>> # Forgot to do "file.seek(0)" here
>>> s = mmap.mmap(file.fileno(), 5)
>>> s[:5]
Bus error
[dalke@pw600a src]$ gdb ./python core
GNU gdb 19991004
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General 
Public License, and you are
welcome to change it and/or distribute copies of it 
under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show 
warranty" for details.
This GDB was configured as "alpha-redhat-linux"...

warning: "/home/dalke/cvses/python/dist/src/core": 
ambiguous core format, 2 handle
rs match

warning: core file may not match specified executable 
file.
Core was generated by `perl'.
Program terminated with signal 8, Floating point 
exception.
#0  0x12004d7b8 in com_assert_stmt (c=0x0, n=0x0) at 
Python/compile.c:717
717             PyString_AsString(c->c_code)[c-
>c_nexti++] = byte;
(gdb) where
#0  0x12004d7b8 in com_assert_stmt (c=0x0, n=0x0) at 
Python/compile.c:717
(gdb)

                     Andrew
                     dalke@dalkescientific.com


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>Comment By: Neal Norwitz (nnorwitz)
Date: 2002-09-11 23:39

Message:
Logged In: YES 
user_id=33168

This bug was fixed by fixing bug 585792.

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

Comment By: Andrew Dalke (dalke)
Date: 2002-04-05 07:04

Message:
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user_id=190903

The patch (against current CVS as of 2002 April 05)
passes the regression above, by raising an OSError
exception instead of giving a bus error, which is
the case without the patch.

I don't know enough about mmap, but the code and
explanation looks reasonable.  The exception text given
is good enough that I could figure out how to fix
my problem/misunderstanding.


The regression test tests this bug.  However, there
is a small typo in the patch to test_mmap.py.  Line
277 says

  ... not in ('win32'):
when it should say
  ... not in ('win32', ):


+1 on accepting the gist of this patch (with this fix).


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

Comment By: Guido van Rossum (gvanrossum)
Date: 2002-04-04 12:22

Message:
Logged In: YES 
user_id=6380

Note that Greg Green has uploaded a fix for this, patch
536578.

Andrew, can you test that patch?

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

Comment By: Jeremy Hylton (jhylton)
Date: 2001-10-22 19:37

Message:
Logged In: YES 
user_id=31392

I can reproduce the problem just fine on Intel Linux, but
I'm not really sure what we can do about it.  When I run the
test, I get a bus error when it tries to dereference
self->data in mmap_slice().  I don't see how we can prevent
the bus error short of checking the length of the file
before we map it.


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

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