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)...