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Date:	Mon, 05 Sep 2011 14:20:38 +0200
From:	Marco atzeri <marco DOT atzeri AT gmail DOT com>
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To:	cygwin <cygwin AT cygwin DOT com>
Subject:	debugging SIGSEV on pclose
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Hi,
I am trying to identify the octave segfault, last reported on
http://cygwin.com/ml/cygwin-announce/2011-08/msg00003.html

To reproduce: run octave from xterm and at prompt
-------------------------
  graphics_toolkit ("fltk")
  x=1:10;
  plot(x,x)
  print("fltk.png","-dpng")
-------------------------
the plot is built and printed as file but octave crashes.


After builiding cygwin (cvs), octave and fltk with
gcc-4.5.3 I was able to identify the SIGSEV in cygwin pclose.

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 5980.0x164c]
pclose (fp=0x7ffdf000) at 
/pub/cygwin/cvs/src_new/winsup/cygwin/syscalls.cc:4026
4026      if (fh->get_device () != FH_PIPEW && fh->get_device () != 
FH_PIPER)
(gdb) l
4021    int
4022    pclose (FILE *fp)
4023    {
4024      fhandler_pipe *fh = (fhandler_pipe *) cygheap->fdtab[fileno(fp)];
4025
4026      if (fh->get_device () != FH_PIPEW && fh->get_device () != 
FH_PIPER)
4027        {
4028          set_errno (EBADF);
4029          return -1;
4030        }

the pclose is relative to a single popen call:

Breakpoint 1, popen (
     command=0x207e969c "/usr/bin/gs -dQUIET -dNOPAUSE -dBATCH -dSAFER 
-sDEVICE=png16m -dTextAlphaBits=4 -dGraphicsAlphaBits=4 -r150x150 
-dEPSCrop -sOutputFile=fltk.png -", in_type=0x1a45b18 "w")
     at /pub/cygwin/cvs/src_new/winsup/cygwin/syscalls.cc:3920
3920    {

and the SIGSEV seems to happen inside NTDLL

Program received signal SIGSEGV, Segmentation fault.
0x7c90e514 in ntdll!LdrAccessResource ()
    from /cygdrive/c/WINDOWS/system32/ntdll.dll
(gdb) bt
#0  0x7c90e514 in ntdll!LdrAccessResource ()
    from /cygdrive/c/WINDOWS/system32/ntdll.dll
#1  0x7c90df5a in ntdll!ZwWaitForSingleObject ()
    from /cygdrive/c/WINDOWS/system32/ntdll.dll
#2  0x7c8025db in WaitForSingleObjectEx ()
    from /cygdrive/c/WINDOWS/system32/kernel32.dll
#3  0x0000046c in ?? ()
#4  0x00000000 in ?? ()
(gdb)

At this point I am really lost as I have no clue of the
popen/pclose internal interaction, so any suggestion is
really appreciated

thanks
Marco

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