debugging SIGSEV on pclose

Marco atzeri marco.atzeri@gmail.com
Thu Sep 8 16:20:00 GMT 2011


On 9/8/2011 5:12 PM, Marco atzeri wrote:
> On 9/8/2011 4:27 PM, Christopher Faylor wrote:
>> On Thu, Sep 08, 2011 at 04:15:47PM +0200, Marco atzeri wrote:
>
>>> Question:
>>> is a mistake in pclose to assume that fh could be invalid
>>
>> I'm not sure what you're asking here. It's not a mistake to assume that
>> pclose is being passed a valid fp. Linux also crashes if the fp is
>> closed twice.
>
> Just as I noticed earlier on syscall.cc a defensive approuch
>
> -----------------------------------------------
> close_all_files (bool norelease)
> {
> cygheap->fdtab.lock ();
>
> semaphore::terminate ();
>
> fhandler_base *fh;
> HANDLE h = NULL;
>
> for (int i = 0; i < (int) cygheap->fdtab.size; i++)
> if ((fh = cygheap->fdtab[i]) != NULL)
> {
> ------------------------------------------------

using the same defensive approuch on pclose,
I see no more SEGFAULT, just some lost popen childs
that are closed on octave exit.

--- syscalls.cc~        2011-08-02 20:19:18.000000000 +0200
+++ syscalls.cc 2011-09-08 16:31:03.109375000 +0200
@@ -4023,7 +4023,7 @@
  {
    fhandler_pipe *fh = (fhandler_pipe *) cygheap->fdtab[fileno(fp)];

-  if (fh->get_device () != FH_PIPEW && fh->get_device () != FH_PIPER)
+  if ( !fh ||(fh->get_device () != FH_PIPEW && fh->get_device () != 
FH_PIPER))
      {
        set_errno (EBADF);
        return -1;


Does it make sense ?

>
>>
>>> or something is just trashing cygheap->fdtab ?
>>
>> Who knows? strace should show if the fp is closed twice.
>>
>> cgf
>
> correct, it looks I have two close in excess for fd 5 and 6
>
> Thanks
> Marco
>
>

too fast, the mismatch are the pipe closure,
that are reported differently as opening

I see a double pipe closure

$ grep 'pipe:\[5\]'  octave.strace
    24     595 [main] sh 2840 fhandler_base::fixup_after_exec: here for 
'/dev/fd/pipe:[5]'
    35 103396815 [main] octave-3.4.2 3664 fhandler_base::close: closing 
'/dev/fd/pipe:[5]' handle 0x46C
    37     896 [main] gs 2840 fhandler_base::fixup_after_exec: here for 
'/dev/fd/pipe:[5]'
    48   93072 [main] sh 2840! fhandler_base::close: closing 
'/dev/fd/pipe:[5]' handle 0x46C
    31 2358333 [main] gs 2840 fhandler_base::close: closing 
'/dev/fd/pipe:[5]' handle 0x46C

but I guess they are the two sides of the pipe


spawn_guts: 2840 = spawn_guts (/bin/sh, E:\cygwin2\bin\sh.exe -c 
"/usr/bin/gs -dQUIET -dNOPAUSE -dBATCH -dSAFER -sDEVICE=png16m 
-dTextAlphaBits=4 -dGraphicsAlphaBits=4 -r150x150 -dEPSCrop 
-sOutputFile=plot.png -")


Marco


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