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Message-ID: <5211F83A.30901@cs.utoronto.ca>
Date: Mon, 19 Aug 2013 06:49:30 -0400
From: Ryan Johnson <ryan DOT johnson AT cs DOT utoronto DOT ca>
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To: cygwin AT cygwin DOT com
Subject: Re: Stack size on 64-bit Cygwin
References: <520E905A DOT 409 AT cornell DOT edu> <20130819093242 DOT GB18757 AT calimero DOT vinschen DOT de>
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On 19/08/2013 5:32 AM, Corinna Vinschen wrote:
> On Aug 16 16:49, Ken Brown wrote:
>> The problem that has been discussed at length in the thread "64-bit
>> emacs crashes a lot" appears to have been solved on the emacs-devel
>> list.  (I say "appears to" because I'm waiting for Ryan to confirm
>> this.)  The problem went away for me when I built emacs with
>> 'LDFLAGS=-Wl,--stack,4194304'.  I'm wondering if it's just that
>> emacs needs an unusually big stack or if the default stack size on
>> 64-bit Cygwin should be increased for all applications.
>>
>> I noticed that ulimit -s gives 2025 on both 32-bit Cygwin and 64-bit
>> Cygwin.  Shouldn't 64-bit applications need a larger stack than
>> 32-bit applications in general?
>  From my POV, if you have a stack-active application, just add the
> aforementioned --stack linker option, or call peflags -x after the
> build.  The latter can be done any time
FYI, I just tried upping the stack size on /usr/bin/emacs-nox, but it 
still crashes. Most likely because the damage was already done during 
bootstrap, when it has much larger memory requirements than normal.

Still no crashes so far in the version I linked with --stack, though.

One thing I don't understand, though: shouldn't a stack overflow 
normally manifest as a seg fault when trying to access the invalid 
addresses, rather than silent memory corruption?

However, /proc/pid/maps for emacs shows:
> 00010000-00020000 rw-s 00000000 0000:0000 0                   [win 
> heap 1 default shared]
> 00020000-00030000 rw-s 00000000 0000:0000 0                   [win 
> heap 2 default shared]
> 00030000-001E4000 ===p 00000000 0000:0000 0 [stack (tid 4896)]
> 001E4000-001E6000 rw-g 001B4000 0000:0000 0 [stack (tid 4896)]
> 001E6000-00230000 rw-p 001B6000 0000:0000 0 [stack (tid 4896)]
GDB reports that thread 4896 is the main thread... so I guess Windows 
doesn't reserve a red zone around its stack, but instead chooses to 
place the main thread stack right next to the fully-mapped global shared 
heap to maximize the potential for Fun?

Ryan


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