This is the mail archive of the cygwin mailing list for the Cygwin project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Stack size on 64-bit Cygwin


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


--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]