[PATCH] Setting TZ may break time() in non-Cygwin programs

[Christian Franke]

Christopher Faylor wrote:
> On Tue, Apr 17, 2012 at 09:06:15AM +0200, Corinna Vinschen wrote:
>> On Apr 11 20:52, Christian Franke wrote:
>>> Yes. Patch is attached.
>>>
>>> Christian
>>>
>> Thanks for the patch.  I'm just wondering if we shouldn't generalize
>> this right from the start by keeping an array of variables to skip
>> when starting native apps and a function to handle this, along the
>> lines of the getwinenv function and the conv_envvars array.
>> It might only contain TZ now, but there's always a chance we suddenly
>> stumble over a similar problem, isn't it?
> I really hate having Cygwin be "smart" like this.  It seems like it's
> asking for a follow-on "How do I set TZ for my Windoze program???"
> email, followed by a "We need a CYGWIN environment variable option!"
>
> What's the problem with just unsetting TZ again?  Yes, I know you
> have to remember to do it but does this affect enough programs that
> we need to add even more head standing code in Cygwin to accommodate
> it.

It affects all C/C++ programs which use time() and friends from any 
version of MSVCRT as DLL or static library.

Which means that cygcheck is also affected:

$ echo $TZ
Europe/Berlin

$ objdump -p /bin/cygwin1.dll | grep 'Time/Date[^ ]'
Time/Date               Sun Apr 15 19:56:27 2012

$ cygcheck -v /bin/cygwin1.dll | grep 'cygwin1.*ts'
   "cygwin1.dll" v0.0 ts=2012/4/15 18:56

$ export TZ=America/Los_Angeles

$ objdump -p /bin/cygwin1.dll | grep 'Time/Date[^ ]'
Time/Date               Sun Apr 15 10:56:27 2012

$ cygcheck -v /bin/cygwin1.dll | grep 'cygwin1.*ts'
   "cygwin1.dll" v0.0 ts=2012/4/15 18:56

$ unset TZ

$ objdump -p /bin/cygwin1.dll | grep 'Time/Date[^ ]'
Time/Date               Sun Apr 15 19:56:27 2012

$ cygcheck -v /bin/cygwin1.dll | grep 'cygwin1.*ts'
   "cygwin1.dll" v0.0 ts=2012/4/15 19:56


In this case the effect is harmless. In other cases it may break 
functionality.

Christian