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X-HELO:	cliff.scrc.umanitoba.ca
Subject:	Re: libharfbuzz0 1.7.6-1 update causing xwin-xdg-menu.exe to crash
To:	The Cygwin Mailing List <cygwin AT cygwin DOT com>
References:	<30aa068b-574f-8770-d8f3-eb037c038709 AT scrc DOT umanitoba DOT ca> <63a969f7-00eb-2067-7dbe-f141bfecbaae AT dronecode DOT org DOT uk>
From:	Gilles Detillieux <grdetil AT scrc DOT umanitoba DOT ca>
Message-ID:	<45934aef-f59b-7ca6-5cf9-8e60ad559cae@scrc.umanitoba.ca>
Date:	Thu, 26 Apr 2018 10:40:01 -0500
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In-Reply-To:	<63a969f7-00eb-2067-7dbe-f141bfecbaae@dronecode.org.uk>

On 2018-04-26 09:03, Jon Turney wrote:
> On 19/04/2018 22:15, Gilles Detillieux wrote:
>> Has anybody else run into this problem? I've done two installations 
>> of Cygwin/X on Windows 10 systems this week, and they both had 
>> problems with the XWin Server dying just a few seconds after starting 
>> up. I traced the problem back to xwin-xdg-menu.exe getting a 
>> Segmentation fault, which then causes XWin Server to exit. I hacked 
>> an alternate .startxwinrc file to prevent XWin Server from dying (it 
>> ends with a "sleep infinity"), so I could debug it further.
>>
>> With the XWin Server running reliably, I then ran "strace 
>> xwin-xdg-menu.exe" and saw that it got a segmentation fault just 
>> after reading a TTF font from the Windows Font directory 
>> (bahnschrift.ttf if it matters). I noticed there were two recent 
>> library updates related to font handling, so I tried back out to the 
>> previous version for each. It turns out that when I reverted to 
>> version 1.7.4-1 of libharfbuzz0, xwin-xdg-menu.exe stopped crashing.
>>
>> If it matters, both these systems are the Fall Creator's Update 
>> (1709) of Windows 10 64-bit, and I'm running the 32-bit version of 
>> Cygwin.
>>
>> Hopefully someone can track down and fix this recent bug!
>
> Thanks for reporting this.
>
> I can reproduce this problem, but it only seems to occur with 32-bit 
> cygwin.
>
> (Obviously you also need a recent enough Windows 10 to have the 
> Bahnschrift font)
>
> The actual crash seems to be in fontconfig, e.g. 'fc-query 
> /usr/share/fonts/microsoft/bahnschrift.ttf' fails in the same way.
>
> I didn't get very far investigating the problem, as rebuilding the 
> fontconfig package with the current toolchain seems to be enough to 
> make the problem go away.

Thanks for the follow-up and narrowing down the problem, Jon. 
Interesting that rebuilding fontconfig clears up the issue. Although, if 
it's a memory corruption issue, it could just be that the new toolchain 
lays things out differently enough that the bug doesn't manifest itself 
the same way. It could also be that the new gcc fixes a compiler or 
optimizer bug that led to the problem. Perhaps you and Yaakov could 
touch base on which toolchain versions you're using and see if an update 
to his toolchain may be in order.

Are you using the test version of gcc (7.3.0-1) announced April 11, or 
the older release. I've got gcc-core-6.4.0-5 on mine, which I assume is 
the latest stable release.

-- 
Gilles R. Detillieux              E-mail: <grdetil AT scrc DOT umanitoba DOT ca>
Spinal Cord Research Centre       WWW:    http://www.scrc.umanitoba.ca/
Dept. of Physiology and Pathophysiology, Faculty of Health Sciences,
Univ. of Manitoba  Winnipeg, MB  R3E 0J9  (Canada)


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