On Mon, Sep 27, 2010 at 9:51 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: > 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).
I just copied the rule from %/config-devices.mak. Is also that rule then incorrect? Perhaps there could be a macro for this, not unlike move-if-change script in various GNU packages?
