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Date: Tue, 14 May 2013 15:39:50 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: mktime loop
Message-ID: <20130514133950.GC23910@calimero.vinschen.de>
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References: <5244063b734b165baf34bdebaff0aca5 AT denis-excoffier DOT org> <20130513153651 DOT GD5045 AT calimero DOT vinschen DOT de> <20130513154921 DOT GF8890 AT calimero DOT vinschen DOT de> <27BBE8FE-303A-432D-94AA-AF834124D125 AT Denis-Excoffier DOT org> <20130513165712 DOT GH8890 AT calimero DOT vinschen DOT de>
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User-Agent: Mutt/1.5.21 (2010-09-15)

On May 13 18:57, Corinna Vinschen wrote:
> On May 13 18:41, Denis Excoffier wrote:
> > On 2013-05-13 17:49, Corinna Vinschen wrote:
> > > Erm... hang on.  Is that really a problem?  2147483647 is 0x7fffffff,
> > > which is the maximum you get with a 4 byte time_t (== signed long)
> > > anyway.  If you switch the date to 2038-01-20, the value will be
> > > negative, and therefore outside the scope of the 4 byte time_t.  So this
> > > is a hard restriction of using 4 byte time_t.
> > > 
> > > The solution is:
> > > 
> > > - Either somebody changes 32 bit Cygwin to 8 byte time_t while keeping
> > >  all the 4 byte time_t APIs intact to maintain compatibility with
> > >  existing binaries(*),
> > > 
> > > - or, you switch to a 64 bit Windows and use 64 bit Cygwin ;)
> > > 
> > I understand.
> > 
> > I suppose you will however be willing to provide us a means to workaround
> > the "autoconf mktime usability test failing" (see for example in
> > gawk-4.1.0 where all the tm fields are set to 128). Now, instead of only
> > failing (i presume), it hangs. Sorry, this specific point should have been
> > noticed in my original post.
> > 
> > Or do we have to patch every impacted ./configure?
> 
> Good point.  I guess the right thing to do here is for mktime to
> return -1 instead of hanging.  I look into that.

Looks like this is a result of gcc optimization settings.  The upstream
code computing time_t <-> struct tm conversions requires integer
overflow to be fully defined, but gcc's -O2 option sets
-fstrict-overflow which results in all kinds of agressive integer
optimizations which disabled utilizing integer overflows for serious
purposes.  I fixed that by setting the -fwrapv option when building the
affected localtime.cc file (thanks to Kai Tietz for pointing this out).


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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