On Thu, Aug 21, 2014 at 4:32 PM, Eric Blake <eblake@xxxxxxxxxx> wrote: > Make folks: > You may want to check out http://austingroupbugs.net/view.php?id=857 and > add comments and/or change GNU make behavior accordingly. There, the > argument is made that HP-UX make behavior is nicer than GNU's current > behavior when two files have identical timestamps: HP-UX considers the > file as out-of-date, while GNU make considers it up-to-date. A strict > reading of POSIX can argue that GNU's behavior was required, but this > reading has been called into question. > > GNU's behavior is an optimization that avoids needless churn on file > systems with course timestamps (well, FAT still exists, but these days, > MOST file systems have sub-second resolution, so it is harder to get > files with identical timestamps without actually touch'ing them that > way) - but it risks leaving a tree in an incomplete state. HP-UX > behavior guarantees the rules are run, even if they were not strictly > necessary, but has the nice property that the tree is never left in an > incomplete state due to unfortunate timing on a file system with course > timestamps. > > The POSIX recommendation was therefore that GNU should change its > behavior to act like HP-UX, and consider identical timestamps as > out-of-date, because the standard will be fixed to allow HP-UX behavior. > > Autoconf folks: > The section of the autoconf manual that discusses this should probably > be modernized, particularly if changes to POSIX and/or GNU make result > from this discussion. > https://www.gnu.org/software/autoconf/manual/autoconf.html#Timestamps-and-Make > Some projects that want to have deterministic builds by using the gitian builder [1] use libfaketime to set the timestamps to a known constant, and gnu make trips up on this, occasionally causing broken builds and othertimes autoconf declares suck a build system "insane". There was a bug in libfaketime so that the nanosecond field wasn't cleared and this allowed you to avoid both these bugs if the planets were aligned correctly (which has since been fixed). I agree that these issues should be fixed in make and autoconf. [1] https://gitian.org/ > -- > Eric Blake eblake redhat com +1-919-301-3266 > Libvirt virtualization library http://libvirt.org > > > _______________________________________________ > Bug-make mailing list > Bug-make@xxxxxxx > https://lists.gnu.org/mailman/listinfo/bug-make > _______________________________________________ Autoconf mailing list Autoconf@xxxxxxx https://lists.gnu.org/mailman/listinfo/autoconf
