On Mar 13, 2016 11:26 PM, "Masahiro Yamada" <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > Hi Andy, > > > 2016-03-14 13:44 GMT+09:00 Andy Lutomirski <luto@xxxxxxxxxxxxxx>: > > On Sun, Mar 13, 2016 at 9:36 PM, Masahiro Yamada > > <yamada.masahiro@xxxxxxxxxxxxx> wrote: > >> 2016-03-14 13:28 GMT+09:00 Andy Lutomirski <luto@xxxxxxxxxxxxxx>: > >>> On Sun, Mar 13, 2016 at 9:08 PM, Masahiro Yamada > >>> <yamada.masahiro@xxxxxxxxxxxxx> wrote: > >>>> > >>>> Hi Andy > >>>> > >>>> 2016-03-14 9:39 GMT+09:00 Andy Lutomirski <luto@xxxxxxxxxxxxxx>: > >>>> > On Mar 12, 2016 4:14 PM, "Masahiro Yamada" > >>>> > <yamada.masahiro@xxxxxxxxxxxxx> wrote: > >>>> >> > >>>> >> These targets are marked as PHONY. No need to add FORCE to their > >>>> >> dependency. > >>>> > > >>>> > If this is, in fact, correct, can you update > >>>> > Documentation/kbuild/makefiles.txt as well? > >>>> > >>>> Which line do you want me to update? > >>>> > >>> > >>> All the references to FORCE should probably mention .PHONY as an alternative. > >> > >> I do not get your point. > >> > >> All the examples in the makefile.txt correctly reference to FORCE. > >> They are not PHONY targets. > >> No need to update. > > > > But they could be. For example: > > > > $(obj)/image: vmlinux FORCE > > $(call if_changed,objcopy) > > > > could be: > > > > .PHONY: $(obj)/image > > $(obj)/image: vmlinux > > $(call if_changed,objcopy) > > > > I would at least change: > > > > Note: It is a typical mistake to forget the FORCE prerequisite. > > > > to: > > > > Note: if-changed is only useful if make executes it, which won't > > happen if it determines that the inputs have not changed since the > > output was built. This can be avoided by specifying FORCE as a > > prerequisite or by making declaring the output as .PHONY. > > > > > No. This is absolutely wrong. > PHONY and FORCE are not interchangeable. > > They have different behavior. > I will show you how they behave differently. > > > BTW, Linux 4.5 is out now. > > Let's try a simple experiment on it. > > > The following shows that my source tree is v4.5 > > yamada@beagle:~/workspace/linux$ git describe > v4.5 > > > > Example 1) > > > Add the following code to the top Makefile. > > Please note "FORCE" is used here. > > > yamada@beagle:~/workspace/linux$ git diff > diff --git a/Makefile b/Makefile > index 7b3ecdc..89b7d0d 100644 > --- a/Makefile > +++ b/Makefile > @@ -914,6 +914,22 @@ export KBUILD_ALLDIRS := $(sort $(filter-out > arch/%,$(vmlinux- > > vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_INIT) $(KBUILD_VMLINUX_MAIN) > > +quiet_cmd_gen_foo = FOO $@ > + cmd_gen_foo = (cat $<; echo hello) > $@ > + > +foo: bar FORCE > + $(call if_changed,gen_foo) > + > +quiet_cmd_gen_bar = BAR $@ > + cmd_gen_bar = (cat $<; echo $(GREETING)) > $@ > + > +bar: baz FORCE > + $(call if_changed,gen_bar) > + > +baz: > + @touch $@ > + > + > # Final link of vmlinux > cmd_link-vmlinux = $(CONFIG_SHELL) $< $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) > quiet_cmd_link-vmlinux = LINK $@ > > > > Try the following. > > yamada@beagle:~/workspace/linux$ git clean -x -f > yamada@beagle:~/workspace/linux$ make -s defconfig > yamada@beagle:~/workspace/linux$ make GREETING=GoodMorning foo > scripts/kconfig/conf --silentoldconfig Kconfig > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodMorning foo > make: `foo' is up to date. > yamada@beagle:~/workspace/linux$ make GREETING=GoodAfternoon foo > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodAfternoon foo > make: `foo' is up to date. > yamada@beagle:~/workspace/linux$ make GREETING=GoodEvening foo > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodEvening foo > make: `foo' is up to date. > > > > > Please notice "foo" and "bar" were not rebuilt > when I gave the same command line as the previous run. > > > When I changed the command line, "bar" was update > and "foo" was also updated because "foo" depends on "bar". > > > It means $(call if_changed,...) is working as expected. > > > > > > > Example 2) > > > Add the following to the top Makefile. > Please notice that I just replaced "FORCE" with ".PHONY". > > > > diff --git a/Makefile b/Makefile > index 7b3ecdc..a0899c3 100644 > --- a/Makefile > +++ b/Makefile > @@ -914,6 +914,24 @@ export KBUILD_ALLDIRS := $(sort $(filter-out > arch/%,$(vmlinux- > > vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_INIT) $(KBUILD_VMLINUX_MAIN) > > +quiet_cmd_gen_foo = FOO $@ > + cmd_gen_foo = (cat $<; echo hello) > $@ > + > +.PHONY: foo > +foo: bar > + $(call if_changed,gen_foo) > + > +quiet_cmd_gen_bar = BAR $@ > + cmd_gen_bar = (cat $<; echo $(GREETING)) > $@ > + > +.PHONY: bar > +bar: baz > + $(call if_changed,gen_bar) > + > +baz: > + @touch $@ > + > + > # Final link of vmlinux > cmd_link-vmlinux = $(CONFIG_SHELL) $< $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) > quiet_cmd_link-vmlinux = LINK $@ > > > > Let's try the same thing. > > > > yamada@beagle:~/workspace/linux$ git clean -x -f > yamada@beagle:~/workspace/linux$ make -s defconfig > yamada@beagle:~/workspace/linux$ make GREETING=GoodMorning foo > scripts/kconfig/conf --silentoldconfig Kconfig > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodMorning foo > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodMorning foo > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodAfternoon foo > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodAfternoon foo > BAR bar > FOO foo > yamada@beagle:~/workspace/linux$ make GREETING=GoodAfternoon foo > BAR bar > FOO foo > > > Did you notice the difference? > > The "foo" and "bar" are always rebuilt > regardless the command line is changed or not. > > It means $(call if_changed,...) is not working. > Fair enough, although I'm curious why this happens. It might be worth changing the docs to say that .PHONY is *not* an substitute for FORCE in that context, then. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
