On 06/14/2016 06:26 AM, Stefan Hajnoczi wrote: > On Thu, Jun 09, 2016 at 05:57:55PM +0100, Daniel P. Berrange wrote: >> +$(BUILD_DIR)/trace-events-all: $(trace-events-y:%=$(SRC_PATH)/%) >> + $(call quiet-command,cat $^ > $@) > > $^ needs to be a stable ordering across make invocations and across > machines to avoid thrashing ccache and spuriously renumbering trace > event IDs. > > I guess it is stable but just in case anyone knows of a case where $^ > would change order without any changes to the actual files (e.g. > readdir(2) returning things in a different order, make parallel jobs, > etc)...
As far as I can tell from 'info make', $^ is the list of prerequisites, _in prerequisite order_, minus duplicates. So the only way the order will change is if you edit Makefile, and thus it looks stable to me. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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