prerequisites alter choice of pattern match rules?
Hi, I have run into something I find strange with GNU Make 3.81 (yes, I know 3.82 is latest but since it's not in EL6, my target platform, I cannot depend on it's features). I would think that given the following set of rules: /tmp/%.foo: %.foo echo foo rule 1 touch $@ %.foo: echo foo rule 2 touch $@ /tmp/%.bar: make $*.bar echo bar rule 1 touch $@ %.bar: echo bar rule 2 touch $@ Trying to create a target of /tmp/a.foo and /tmp/a.bar should result in the same rules being run but they don't: $ ls -l . /tmp/a.bar /tmp/a.foo ls: cannot access /tmp/a.bar: No such file or directory ls: cannot access /tmp/a.foo: No such file or directory .: total 4 -rw-rw-r--. 1 brian brian 176 Feb 25 08:48 Makefile $ make /tmp/a.foo echo foo rule 2 foo rule 2 touch /tmp/a.foo $ make /tmp/a.bar make a.bar make[1]: Entering directory `/home/brian/chroma/deps/lustre/test' echo bar rule 2 bar rule 2 touch a.bar make[1]: Leaving directory `/home/brian/chroma/deps/lustre/test' echo bar rule 1 bar rule 1 touch /tmp/a.bar It would seem that for the /tmp/a.foo, the /tmp/%.foo pattern rule is not being chosen but for /tmp/a.bar the /tmp/%.bar pattern rule is being chosen. The only difference in those choices I can see is that the /tmp/%.foo pattern rule has a prerequisite and the /tmp/%.bar one doesn't. So the question is, why does a prerequisite change the behavior of pattern match rules? I would think the selection of a pattern match rule would be independent of prerequisites but of course once the pattern match rule was chosen, the rule for the prerequisite would also need to be called to ensure it's freshness. Thoughts? b. signature.asc Description: OpenPGP digital signature ___ Bug-make mailing list Bug-make@gnu.org https://lists.gnu.org/mailman/listinfo/bug-make
Re: prerequisites alter choice of pattern match rules?
On 25.02.2013 14:57, Brian J. Murrell wrote: Hi, I have run into something I find strange with GNU Make 3.81 (yes, I know 3.82 is latest but since it's not in EL6, my target platform, I cannot depend on it's features). I would think that given the following set of rules: /tmp/%.foo: %.foo echo foo rule 1 touch $@ %.foo: echo foo rule 2 touch $@ /tmp/%.bar: make $*.bar echo bar rule 1 touch $@ %.bar: echo bar rule 2 touch $@ [..] $ make /tmp/a.foo echo foo rule 2 foo rule 2 touch /tmp/a.foo $ make /tmp/a.bar make a.bar make[1]: Entering directory `/home/brian/chroma/deps/lustre/test' echo bar rule 2 bar rule 2 touch a.bar make[1]: Leaving directory `/home/brian/chroma/deps/lustre/test' echo bar rule 1 bar rule 1 touch /tmp/a.bar It would seem that for the /tmp/a.foo, the /tmp/%.foo pattern rule is not being chosen but for /tmp/a.bar the /tmp/%.bar pattern rule is being chosen. The only difference in those choices I can see is that the /tmp/%.foo pattern rule has a prerequisite and the /tmp/%.bar one doesn't. Confirming the same behavior for make 3.82. It seems like normally GNU make walks the path of the most specific match in case of ambiguities. I wonder if that's specified/documented anywhere. For this Makefile xxx%: @echo '$@ -- xxx%' x%: @echo '$@ -- x%' xx%: @echo '$@ -- xx%' the most specific rule is chosen one might expect: # make x1 xx2 xxx3 4 x1 -- x% xx2 -- xx% xxx3 -- xxx% 4 -- xxx% Side notes on the above Makefile: - make $*.bar in there does not seem to be relevant. After removing that line, the file still reproduces your case. - make $*.bar should be $(MAKE) $*.bar, use $(MAKE) to invoke make to not run into parallel build issues - To reduce output noise, you can use lines like @echo foo rule 1 ^ instead of echo foo rule 1 So the question is, why does a prerequisite change the behavior of pattern match rules? Good question. Best, Sebastian ___ Bug-make mailing list Bug-make@gnu.org https://lists.gnu.org/mailman/listinfo/bug-make
Re: prerequisites alter choice of pattern match rules?
On Mon, Feb 25, 2013 at 2:30 PM, Sebastian Pipping sebast...@pipping.org wrote: ... It seems like normally GNU make walks the path of the most specific match in case of ambiguities. I wonder if that's specified/documented anywhere. Yes, it is. I don't remember where, but it's in the docs. Philip Guenther ___ Bug-make mailing list Bug-make@gnu.org https://lists.gnu.org/mailman/listinfo/bug-make
Re: prerequisites alter choice of pattern match rules?
On Mon, Feb 25, 2013 at 5:57 AM, Brian J. Murrell br...@interlinx.bc.ca wrote: I would think that given the following set of rules: /tmp/%.foo: %.foo echo foo rule 1 touch $@ %.foo: echo foo rule 2 touch $@ /tmp/%.bar: make $*.bar echo bar rule 1 touch $@ %.bar: echo bar rule 2 touch $@ Trying to create a target of /tmp/a.foo and /tmp/a.bar should result in the same rules being run but they don't: ... It would seem that for the /tmp/a.foo, the /tmp/%.foo pattern rule is not being chosen but for /tmp/a.bar the /tmp/%.bar pattern rule is being chosen. The only difference in those choices I can see is that the /tmp/%.foo pattern rule has a prerequisite and the /tmp/%.bar one doesn't. So the question is, why does a prerequisite change the behavior of pattern match rules? I would think the selection of a pattern match rule would be independent of prerequisites but of course once the pattern match rule was chosen, the rule for the prerequisite would also need to be called to ensure it's freshness. Thoughts? When there's no explicit rule for a target (i.e., a rule where the exact target name is listed), the algorithm for chosing the implicit rule to apply first checks for rule(s) for which all the prerequisites either already exist or are explicitly listed as targets themselves, or have no prerequisites**. Only if all the pattern rules have at least one non-existent prerequisite that isn't explicitly listed elsewhere does make then recursively try chaining to other rules for each of the (missing) prerequisites. Yes, this behavior is documented in the info pages in more than sufficient detail to be sure that it was clearly intended. You ask why that's done. To really answer that question I think you would have to find and review the discussions among the developers when it was actually added to GNU make, presumably back when Roland was the maintainer. The answer might be because that's how Stu Feldman's version of make did it. Or maybe it was too slow if we tried all the possible chains, and we also wanted some way other than order-in-the-makefile to prefer a rule. Or if there's a direct way to build something, it must obviously be the right choice over something which requires an intermediate file; if you don't want that, then you should craft your patterns and filename choices so that you don't get overlapping patterns! ...but I wasn't there and those are just guesses. Philip Guenther ** if there are no prerequisites, then all of the prereqs are present; the list of missing prereqs is empty. ___ Bug-make mailing list Bug-make@gnu.org https://lists.gnu.org/mailman/listinfo/bug-make
