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Date: Sat, 28 Jun 2014 07:08:42 -0400
From: Ken Brown <kbrown AT cornell DOT edu>
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To: cygwin AT cygwin DOT com
Subject: Re: Crash in g_file_monitor on 32-bit Cygwin
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On 6/27/2014 1:52 PM, Yaakov Selkowitz wrote:
> On 2014-06-27 12:11, Ken Brown wrote:
>> On 6/25/2014 10:17 PM, Ken Brown wrote:
>>> This is a followup to
>>> https://cygwin.com/ml/cygwin/2014-06/msg00324.html, from which I
>>> extracted the following test case:
>>>
>>> $ cat gfile-test.c
>>> #include <stdio.h>
>>> #include <gio/gio.h>
>>>
>>> void
>>> gfile_add_watch (const char *file)
>>> {
>>>    GFile *gfile = g_file_new_for_path (file);
>>>    GFileMonitor *monitor;
>>>    GFileMonitorFlags gflags = G_FILE_MONITOR_NONE;
>>>    monitor = g_file_monitor (gfile, gflags, NULL, NULL);
>>>    if (! monitor)
>>>      printf ("Can't watch file %s\n", file);
>>>    else
>>>      printf ("Watching file %s\n", file);
>>> }
>>>
>>> int
>>> main ()
>>> {
>>>    const char *file = "gfile-test.c";
>>>    gfile_add_watch (file);
>>> }
>>>
>>> $ gcc -g -O0 -o gfile-test $(pkg-config --cflags gio-2.0) gfile-test.c
>>> $(pkg-config --libs gio-2.0)
>>>
>>> In the 64-bit case, this behaves as expected:
>>>
>>> $ ./gfile-test.exe
>>> Watching file gfile-test.c
>>>
>>> In the 32-bit case, however, it crashes.  Running it under gdb shows
>>> that the call to g_file_monitor leads to a SEGV, but I can't tell
>>> exactly where; when I try to single step through the Glib code, I
>>> eventually hit an assertion violation in gdb.  strace shows lots of
>>> exceptions, but I can't make much sense out of it otherwise.
>>
>> I rebuilt glib and gamin without optimization so that I could step
>> through the code in gdb.  But stepping through the code turned out to be
>> unnecessary, because the bug was gone after the rebuilds.  I don't know
>> if optimization was really the issue or whether just rebuilding with the
>> latest tools is what fixed it.
>>
>> My builds can be obtained from
>>
>>    http://sanibeltranquility.com/cygwin/
>>
>> if anyone else wants to try to reproduce this without rebuilding the
>> packages themselves.
>>
>> Yaakov, could you take a look?
>
> Sure.  Are you narrow this down to only one of glib or gamin?

The culprit is gamin, and optimization *is* relevant.  What's strange, 
though, is that when I rebuild it with optimization, my test case hangs 
instead of crashing.  Summary:

- With gamin-0.1.10-14 (and its subpackages), my test case crashes.  The 
outward symptom is that there's no output, but running the test case 
under gdb shows the SEGV.

- If I rebuild gamin without optimization, I don't see any bug.  More 
precisely, I build it using your gamin.cygport with the following line 
added:

   CFLAGS+=" -O0 -g3"

- If I rebuild gamin with optimization (i.e., just using your 
gamin.cygport with no changes), my test case hangs.

Ken


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