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Date: Fri, 9 Dec 2011 18:02:08 +0100
From: Denis Excoffier <cygwin AT Denis-Excoffier DOT org>
To: cygwin AT cygwin DOT com
Subject: Re: gcc-4.5.3 segfaults wrt alloca
Message-ID: <20111209170232.GA6452@po8371>
References: <20111209105801 DOT GA10388 AT po8371> <4EE22156 DOT 4080402 AT cs DOT utoronto DOT ca>
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On Fri, Dec 09, 2011 at 09:55:18AM -0500, Ryan Johnson wrote:
>> On 09/12/2011 5:58 AM, Denis Excoffier wrote:
>> >I use the latest packages and cygwin snapshots. The problem described
>> >below began several snapshots in the past, around beginning of December.
>> >
>> >The following program, with static allocation of a reasonable amount
>> >of data, segfaults, maybe in alloca(). With a smaller size
>> >(eg 10000) it's ok. With new/malloc (even with 100 times more) it's
>> >ok. With C or C++. 100% reproducible.
>> >   unsigned int const SIZE = 689471;
>> >   int foo[SIZE];
>> Reasonable? You're trying to stack-allocate 2.5MB of data. Don't do
>> that -- stack sizes are 2MB or less in most operating systems.
>> Besides, doing anything useful with a buffer that size would
>> completely drown out the overhead of calling malloc.

You're right.

% ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
file size               (blocks, -f) unlimited
open files                      (-n) 256
pipe size            (512 bytes, -p) 8
stack size              (kbytes, -s) 2034
cpu time               (seconds, -t) unlimited
max user processes              (-u) 256
virtual memory          (kbytes, -v) unlimited
% ulimit -s 3000
sh: ulimit: stack size: cannot modify limit: Invalid argument
%

Regards,

Denis Excoffier.

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