On Mar 5 12:35, Corinna Vinschen wrote: > On Mar 5 11:45, Irfan Adilovic wrote: > > On Tue, Mar 4, 2014 at 9:19 AM, Corinna Vinschen wrote: > > > On Mar 3 23:28, Irfan Adilovic wrote: > > >> > tm_gmtoff is not required by the standard: > > >> > http://www.opengroup.org/onlinepubs/009695399/basedefs/time.h.html > > >> > > > >> > However, it is an extension available in the Olson tzcode, which > > >> > cygwin seems to use. Enabling it would seem to be a matter of > > >> > setting -DTM_GMTOFF=tm_gmtoff and adding it to time.h. > > > > > > And same for TM_ZONE. > > > > > >> I have successfully done this and use the tm_gmtoff in my code > > >> actively. Is there a reason this isn't enabled? Is there any interest > > >> in the community to make tm_gmtoff available by default (It's so easy, > > >> it's a shame it's not :-))? > > > > > > It's easy to change the struct, but changing the size of a structure > > > is an incompatible change to existing applications which leads to > > > overwriting memory. > > > > > > A change to Cygwin involves an extra check if the application has been > > > build against an older or a newer version of Cygwin, and to fill the > > > tm_gmtoff/tm_zone structure members dependent on that. So it's not just > > > done by defining TM_GMTOFF and TM_ZONE. > > > > Now that you mention the incompatibility, it seems logical -- the size > > of the struct is hard-coded when allocation frames in the executable > > (or when mallocing), and passing that to the library will write > > tm_gmtoff past the allocated area -- but how can one even try to > > recognize and act upon that at runtime, without recompiling the > > executable? > > The Cygwin DLL can check under which version of the Cygwin DLL an > executable has been compiled. We're using this knowledge already in > other circumstances. If the DLL finds it has been compiled under an old > Cygwin version which doesn't know these new members, it will not try to > read or write these members, if it's an executabled compiled under a > newer DLL which knows these members, it will utilize them. If you're > running a new executable under an old version of the DLL, the members > will probably contain garbage, but that's an unsupported scenario > anyway.
I created new snapshots on http://cygwin.com/snapshots/ which provide tm_gmtoff and tm_zone for executables linked against that version of the DLL. Please note that it's *not* sufficient to install the new DLL for this functionality to get. You *must* install the full snapshot, including libs and header files. Please give this a thorough test. Thanks, Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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