On 06/09/18 12:26, Jan Beulich wrote: >>>> On 06.09.18 at 10:27, <[email protected]> wrote: >> On 06/09/18 10:10, Jan Beulich wrote: >>>>>> On 06.09.18 at 09:34, <[email protected]> wrote: >>>> I've setup a little example Makefile solving the problem (just to show >>>> the correct dependencies, needs to be adapted for naming the .d and .d2 >>>> files and how to build the .d2): >>>> >>>> -->8 snip here 8<-- >>>> >>>> DEPS := tst.d2 >>>> >>>> all: tst $(DEPS) >>> >>> -include $(DEPS) already ought to have the effect of such a dependency, >>> since all makefiles are checked for rules of how to re-make them. >> >> Obviously this isn't the case. Otherwise there would be .d2 files more >> common after doing a make. > > Well, be this (mis?)behavior is what needs explaining first.
In my example Makefile this is working as you are expecting it: even with removing the dependency of "all" on $(DEPS) everything is fine. I suspect there are no .d2 files after the first make due to: DEPS = .*.d DEPS_INCLUDE = $(addsuffix .d2, $(basename $(wildcard $(DEPS)))) In the beginning there is no .d file, so DEPS_INCLUDE will be empty. > >>>> %.o %.d: %.c >>>> gcc -MMD -o $(patsubst %.c,%.o,$<) -c $< >>> >>> Doesn't this result in gcc to be invoked twice, perhaps resulting in >>> corrupt .o and/or .d? I think %.d wants to depend on %.o, without >>> a command. >> >> No, that's perfectly fine. make will invoke the command only once, its >> just not clear for which target (that's the reason I need to use the >> $(patsubst %.c,%.o,$<) instead of $@, which might be the .o _or_ the .d >> file). >> >> From the make docs: >> >> Pattern rules may have more than one target. Unlike normal rules, this >> does not act as many different rules with the same prerequisites and >> recipe. If a pattern rule has multiple targets, make knows that the >> rule’s recipe is responsible for making all of the targets. The recipe >> is executed only once to make all the targets. > > Oh, right. But then there's no need to play games - just use $*. Aah, right. Good idea. > >>>> %: %.o >>>> gcc $< -o $@ >>>> >>>> -include $(DEPS) >>>> >>>> -->8 snip here 8<-- >>>> >>>> So the basic ideas are: >>>> >>>> - add a rule for constructing the .d files >>>> - let the build depend on the .d2 files >>> >>> IOW I wonder whether this really is any different from what we >>> do now (minus bugs/quirks in make itself, of course). And from this >>> as well as your original mail I still don't understand what's actually >>> broken with the current approach. >> >> The main problem is that the .d2 files used for determining which object >> files need to be (re-)built are based on the build before the last one. >> I'm not sure this is always the case, but at least when starting with a >> clean tree I need two invocations of "make" to get all .d2 files built. > > But that's correct: They're not needed _until_ a rebuild happens. > And by way of make's rebuilding of makefiles (if there are suitable > rules) they should appear _before_ any .o gets rebuilt, and even > before make evaluates which ones need rebuilding. Okay. Then the issue I'm after seems to be a different one. And now I know what is wrong with the build in tools/tests/depriv: There are no .o files specified for depriv-fd-checker, so it is built via: gcc $(CFLAGS) depriv-fd-checker.c $(LDFLAGS) -o depriv-fd-checker I'm suspecting the source file is specified via $<, as the resulting command line after touching one of the headers is: gcc $(CFLAGS) depriv-fd-checker.c <all-headers-from-d2-file> $(LDFLAGS) -o depriv-fd-checker So all files the program is depending on are added into the parameters of gcc. This is the reason for the build error I'm seeing. Juergen _______________________________________________ Xen-devel mailing list [email protected] https://lists.xenproject.org/mailman/listinfo/xen-devel
