Re: XWin.exe segmentation fault on Windows 7

[Chris LeBlanc]

On Thu, Aug 9, 2012 at 4:55 PM, Chris LeBlanc  wrote:
> Hi Mark,
>
>> As Jon's reference [1] explains, merely disabling the BLODA might not be
>> sufficient.  You may have to completely uninstall it to be rid of its 
>> effects.
>>
>> *Especially* if it has processes that re-launch themselves on kill; I mean, 
>> how
>> can you know whether you've ruled this particular BLODA out as an explanation
>> for the issue unless you've completely uninstalled it?
>> HTH,
>

In an effort to track down this bug, we tried completely uninstalling
the virus scanner.  XWin.exe is still failing in the same way (even
after another reinstall and rebase).

I compiled xorg with debugging from the source packages, and that
shows the same behaviour.  I can step through the debugger, but the
output is the same as what Jon found in the previous email, failing on
the call to strcpy().  I've logged the gdb output to a file and can
attach it if anyone is interested.

This machine has previously had the NoMachine client installed on it.
I noticed that it used it's own copy of cygwin1.dll, so I uninstalled
this program.  Is there any chance that this is still causing a
problem, even though it's been uninstalled?

Cheers,
Chris

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Re: XWin.exe segmentation fault on Windows 7

[Chris LeBlanc]

Hi Mark,

> As Jon's reference [1] explains, merely disabling the BLODA might not be
> sufficient.  You may have to completely uninstall it to be rid of its effects.
>
> *Especially* if it has processes that re-launch themselves on kill; I mean, 
> how
> can you know whether you've ruled this particular BLODA out as an explanation
> for the issue unless you've completely uninstalled it?
> HTH,

I agree completely.  My preference was to try a reinstall and go from
there since we know Cygwin works fine on a clean Windows 7 install.
Unfortunately our sysadmins don't want to reinstall the OS.

Being a corporate environment there's no chance of running this
machine without the approved virus scanner running.  I'll talk to the
them again and see if they will temporarily uninstall McAfee so we can
see if it's the cause of the problem.

Cheers,
Chris

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Re: XWin.exe segmentation fault on Windows 7

[Chris LeBlanc]

Hi Jon,

Thanks for the excellent response.

> Given you were getting fork problems before this upgrade, this might well be a
> problem with some other software interfering with cygwin's operation. So you
> should take a look at [1], and probably try running XWin with CYGWIN including
> detect_bloda [2]

The only software I found on her computer that is also on that list
was the McAfee virus scanner.  We disabled this and still saw the
problem (though I noticed the process was still running, and
re-launched itself if you killed it!).  I also tried uninstalling some
other software that might have been interfering; such as DVD burning
software, etc. but still saw the problem (even after a reboot and
rebaseall).

I then set the environment variable CYGWIN=detect_bloda  and launched
a bash instance but didn't see any messages about BLODA detected.
This is a nice feature, I'll be sure to use it if I find any more
forking issues in the future.

Our IT staff is pretty good at quick reinstalls, so I've asked them to
reinstall Windows 7 on this machine.  I'm hopeful this will solve the
problem, but if not I'll continue with debugging XWin.

Thanks,
Chris

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XWin.exe segmentation fault on Windows 7

[Chris LeBlanc]

Hi,

I'm trying to help a coworker get Cygwin running on her Windows 7
(64b) machine, but we're seeing a segmentation fault with XWin.exe.
Previous versions of X11 worked fine on this machine, but recently it
has been unable to fork processes.  It's been giving the error "fork:
child -1 - forked process died unexpectedly ...", which is why I've
been trying to upgrade to the most recent version of Cygwin.

Here's a summary of what I've tried today:

-I cleaned up all traces of Cygwin, including all files under the
install directory and all registry keys.

-I Installed the latest version of Cygwin, using setup.exe from
cygwin.com.  I installed the base system plus gcc4, xinit, and
libX11-devel.  No problems with install, and the normal Cygwin
terminal comes up normally.

-the "startx" script won't launch, it gives the following error:
xinit: giving up
xinit: unable to connect to X server" Connection refused
xinit: server error

-It writes to XWin.exe.stackdump (see below).

-As per http://x.cygwin.com/devel/backtrace.html I installed the
tar.bz2 file for version 1.12.3-1 of xorg-server-debuginfo and ran
"gdb --args /usr/bin/XWin -multiwindow".  Here is the output,
unfortunately it seems to be missing symbols for the most important
part (see below).  It's indicating a problem with strcpy() copying
from a NULL source to an address that is out of bounds (presumably
both could cause a segfault), but unfortunately I can't see a line
number or filename for the code that causes this issue.

I tried reinstalling all of the packages, rebooting, and
rebaseall-ing, but none of this has fixed the problem.

Any advice on how to get more debug info?  How hard is it to build
XWin from source?  If it's a minor strcpy() issue it could be a pretty
easy fix.  Any other advice?

Thanks in advance for any help you can offer.

Cheers,
Chris




Output from XWin.exe.stackdump:
Exception: STATUS_ACCESS_VIOLATION at eip=61129F8B
eax=0028D624 ebx= ecx= edx= esi=0028D624 edi=0028AB5C
ebp=0028A968 esp=0028A95C program=C:\cygwin\bin\XWin.exe, pid 6164, thread main
cs=0023 ds=002B es=002B fs=0053 gs=002B ss=002B
Stack trace:
Frame Function  Args
0028A968  61129F8B  (0028D624, , 0028FF14, 771170D5)
0028AA28  6108E2BA  (0028AA58, 611DF23B, 60FE8510, 0068)
0028AB78  6108EB57  (60FE000C, 0005, 0028ABC4, 005C2DE9)
0028AB98  61091F56  (005C2DCE, 005C2DCC, , )
0028ABF8  610D5F05  (6C34, 0001, 0028FD24, 0002)
0028AC38  00528F43  (0002, 0028AC60, 800280E8, 8003A441)
0028ACF8  61007535  (, 0028CD78, 61006B20, )
End of stack trace



$ gdb --args /usr/bin/XWin -multiwindow
GNU gdb (GDB) 7.3.50.20111026-cvs (cygwin-special)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-cygwin".
For bug reporting instructions, please see:
...
Reading symbols from /usr/bin/XWin...Reading symbols from
/usr/lib/debug/usr/bin/XWin.exe.dbg...done.
done.
(gdb) r
Starting program: /usr/bin/XWin -multiwindow
[New Thread 6164.0x1424]
[New Thread 6164.0x1380]
  0 [main] XWin 6164 exception::handle: Exception: STATUS_ACCESS_VIOLATION
454 [main] XWin 6164 open_stackdumpfile: Dumping stack trace to
XWin.exe.stackdump

Program received signal SIGSEGV, Segmentation fault.
strcpy (dst0=0x40010006 , src0=0x0)
at /usr/src/debug/cygwin-1.7.16-1/newlib/libc/string/strcpy.c:86
86while (!DETECTNULL(*aligned_src))
(gdb) bt full
#0  strcpy (dst0=0x40010006 , src0=0x0)
at /usr/src/debug/cygwin-1.7.16-1/newlib/libc/string/strcpy.c:86
dst = 0x40010006 
src = 0x0
aligned_dst = 0x40010006
aligned_src = 0x28a026
#1  0x751d2ad6 in OutputDebugStringA () from
/cygdrive/c/Windows/syswow64/KERNELBASE.dll
No symbol table info available.
#2  0x40010006 in ?? ()
No symbol table info available.
#3  0x in ?? ()
No symbol table info available.
(gdb)

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X11R7.4 and Webex problem, X apps hang

[Chris LeBlanc]

Hello,

Just wanted to mention a bug I've seen with Cygwin, X11R7.4, and Webex
(a Java based meeting and collaboration tool, www.webex.com).  Webex
has the ability to share a users desktop or individual applications
with other people logged into the meeting.

I can run X11 apps from Cygwin nicely, but if I try to run a Webex
"share application" session, it will cause the X11 apps to hang.  I've
been able to use Webex and Cygwin/X prior to X11R7.4.

Unfortunately, there is no information in the X11 logfiles.  Also,
Webex is a closed source Java program, so I have no control over it.

As a test, I tried running a few Cygwin X apps, but using Xwin32
instead of Cygwin's X server (under Windows 2000).  This didn't crash
with Webex, which indicates there is some problem between Cygwin's X
and Webex's share application feature.  Cygwin is at version 1.5.25-15
(updated a couple weeks ago), xorg-server is at 1.5.3-7, and cygcheck
doesn't show any problems.

Sorry in advance for the vague bug report, but its a difficult problem
to debug.  I've suggested our company switch from Webex to a different
product (one that also works under Linux), but they prefer to use
Webex and have asked that I submit this as a bug report.

Cheers,
Chris LeBlanc

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