On 09/27/2010 10:32 AM, Markus Armbruster wrote:
> Why the conditional? cmp -s fails fine when argument files don't exist.
>
> Note that common versions of make including GNU Make do not stat a
> rule's target to check whether the rule changed it. Instead, they
> assume it changed, and remake everything depending on it.
>
> arm...@blackfin:~/tmp$ cat Makefile
> foo: bar
> echo "Remaking foo"
>
> bar:
> [ -f $@ ] || touch $@&& echo "Touched bar"
> arm...@blackfin:~/tmp$ rm -f foo
> arm...@blackfin:~/tmp$ make
> [ -f bar ] || touch bar&& echo "Touched bar"
> Touched bar
> echo "Remaking foo"
> Remaking foo
> arm...@blackfin:~/tmp$ make
> echo "Remaking foo"
> Remaking foo
>
> I doubt your patch avoids churn as advertized with such makes.
Indeed, see how it's done for config-*.h.
# Uses generic rule in rules.mak
trace.h: trace.h-timestamp
trace.h-timestamp: $(SRC_PATH)/trace-events config-host.mak
$(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -h <
$< > $@," GEN trace.h)
@cmp $@ trace.h >/dev/null 2>&1 || cp $@ trace.h
(untested).
Paolo
