Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> writes: > 2018-07-12 20:32 GMT+09:00 Dirk Gouders <dirk@xxxxxxxxxxx>: >> Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> writes: >> >>> 2018-07-09 20:39 GMT+09:00 Dirk Gouders <dirk@xxxxxxxxxxx>: >>>> Dirk Gouders <dirk@xxxxxxxxxxx> writes: >>>> >>>> I think, I solved the puzzle and perhaps, that saves others some time: >>>> >>>> The problem is that "if_changed" was not designed for multiple use >>>> inside a recipe and in the case of compressed/vmlinux, the 2-fold use >>>> created a kind of flip-flop for situations when nothing has to be done >>>> to build the target. >>>> >>>> Because each of the two users of "if_changed" stores it's footprint in >>>> .vmlinux.cmd but that file then isn't re-read, one of the two >>>> "if_changed" calculates that nothing has to be done wheras the other one >>>> recognizes a change in the commandline, because it sees the command-line >>>> for the other part of the reciepe. >>>> >>>> In the next make, the roles flip, because the previously satisfied >>>> "if_changed" now sees the command-line of the other one. And so on... >>>> >>>> I am not a Kbuild expert but the attached patch fixes that problem by >>>> introducing "if_changed_multi" that accepts two commands -- one whose >>>> commandline should be checked and a second one that should be >>>> executed. >>> >>> >>> if_changed should not appear multiple times in one target. >>> >>> I think the simplest fix-up is to >>> create a new command that combines >>> 'cmd_check_data_rel' and 'cmd_ld'. >>> >>> >>> quiet_cmd_link-vmlinux = LD $@ >>> cmd_link-vmlinux = $(cmd_check_data_rel); $(cmd_ld) >>> >>> $(obj)/vmlinux: $(vmlinux-objs-y) FORCE >>> $(call if_changed,link-vmlinux) >>> >>> Kbuild also supports if_changed_rule, >>> but the usage is more complex. >>> >>> There are only a few usages: >>> https://github.com/torvalds/linux/blob/v4.17/scripts/Makefile.build#L288 >> >> Just for completeness I will copy in part of a reply from Kees that >> shows how double-colon rules can also avoid multiple use of if_changed >> for one target: >> >> -$(obj)/vmlinux: $(vmlinux-objs-y) FORCE >> - $(call if_changed,check_data_rel) >> +$(obj)/vmlinux:: $(vmlinux-objs-y) >> + $(call cmd,check_data_rel) >> +$(obj)/vmlinux:: $(vmlinux-objs-y) FORCE >> $(call if_changed,ld) > > It is difficult to use double-colon rules in a _sane_ way. > > The first one just checks data_rel, > but does not actually generate anything. > > Such targets should be marked as .PHONY, > but $(obj)/vmlinux is not a phony target. > This is strange. > >> The combined command seems to have the advantage that every command to >> build the target gets recorded in the .cmd file >> >> A search showed me that we have two more users that use if_changed more >> than once for a single target: >> >> arch/microblaze/boot/Makefile (fourfold) >> arch/sparc/boot/Makefile (2 times twofold) >> >> The sparc case seems to apply to any of the two suggested fixes, > > Neither is correct. > > > $(obj)/uImage: $(obj)/image.gz > $(call if_changed,uimage) > $(call if_changed,uimage.o) > > > should be split into two targets. > > > $(obj)/uImage: $(obj)/image.gz FORCE > $(call if_changed,uimage) > > $(obj)/uImage.o: $(obj)/uImage FORCE > $(call if_changed,uimage.o) > > > It is wrong in multiple ways. FORCE is missing too. > > but >> microblaze uses if_changed in a pattern rule and also makes use of >> parameter arguments in the sub-commands: >> >> $(obj)/simpleImage.%: vmlinux FORCE >> $(call if_changed,cp,.unstrip) >> $(call if_changed,objcopy) >> $(call if_changed,uimage) >> $(call if_changed,strip,.strip) >> @echo 'Kernel: $(UIMAGE_OUT) is ready' ' (#'`cat .version`')' > > > Probably, this is the same. > > Create a target for each step. > > >> In this case, double colons would have a different meaning and the >> combined command solution would result in a change of the sub-commands, >> as well. I note this in case Michal perhaps has other preferences. >> >> >> In addition to extend the documentation, we could modify if_changed to >> warn about it is being used more than once for a target: >> >> # Execute command if command has changed or prerequisite(s) are updated. >> if_changed = $(if $(filter-out undefined,$(origin if_changed_$@)), \ >> @set -e; \ >> echo "Warning: $@: multiple use of if_changed!" >&2; , \ >> @set -e $(eval if_changed_$@ := 1) ; ) \ >> $(if $(strip $(any-prereq) $(arg-check)), \ >> $(echo-cmd) $(cmd_$(1)); \ >> printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, :) >> >> But this fires only if if_changed is actually called and it defines many >> variables for just that purpose, so this is perhaps not what we want... >> > > I do not want to mess up Makefile. > > > Please do this check in scripts/checkpatch.pl > if you want. Thank you for spending your time in the detailed explanation. I will use it to assemble that all to a fix and then send it for review. Dirk -- 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
