Hi, I have implemented the method described on [Paul D. Smith's blog](http://make.mad-scientist.net/papers/multi-architecture-builds/) for multi-architecture builds. This was done for a fortran data assimilation library used at the Canadian Meteorological Center. The project being in fortran 90, there is no clear separation between declaration of interfaces and implementation, such that if only implementation of a function is modified there is no simple way to tell `make` not to recompile every dependent objects but simply the one modified and proceed with relinking.
We tried to use `make --touch` to indicate not to recompile certain objects for these case, but through the [`target.mk` out-of-tree strategy](http://make.mad-scientist.net/papers/multi-architecture-builds/#target.mk) it also touches empty files (named after the targets of the `make --touch` in the `Makefile` directory, cluttering it with a lot of useless files... I created a simplified `Makefile` that reproduce that issue, which could be accessed at https://gitlab.com/martn/makeTouchIssue Would you be aware of a way to resolve that and keep the out-of-tree compilation working? For sake of completeness, I include here the description of the simplified reproduction of the potential issue that one would find in the gitlab project `README.md` The gitlab project itself can be cloned to reproduce the simplified usecase issue. Regards, -- Martin Deshaies-Jacques Spécialiste en sciences physiques | Physical sciences specialist Environnement et Changement Climatique Canada | Environment and Climate Change Canada Recherche en qualité de l'air | Air Quality Research Division 2121, Autoroute transcanadienne, Dorval (Québec) H9P 1J3 514.421.5304
# `make --touch` issue with out-of-tree Makefile strategy We use the [out-of-tree compilation strategy](http://make.mad-scientist.net/papers/multi-architecture-builds/#advanced) described by [Paul D. Smith](http://mad-scientist.net/). However it seems it interfere with the `--touch` feature of `make`. In the simplified `make` scenario, we are building a program `pgm.x` that depends on 2 objects: `file1.o` and `file2.o` in which the later use a function contained in `file1.o`; this is why the `Makefile` have: ```make file2.o: file1.o ``` ## Problematic usecase Let say, after a full build ``` $ make compiling file1.o compiling file2.o compiling pgm.o linking pgm.x : $ tree build/ build/ âââ file1.o âââ file2.o âââ pgm.o âââ pgm.x 0 directories, 4 files $ make make[1]: Nothing to be done for 'all'. : ``` A developper changes the content of a function in `src/file1.f90` in a way that **does not modify the function interface** and recompile the object: ``` $ touch src/file1.f90 # modifying func1 implementation $ make file1.o compiling file1.o : ``` Although `file1.o` needed to be recompiled, neither `file2.o` nor `pgm.o` need to be recompiled. Obviously, `make` can't know that: ``` $ make -n [ -d build ] || mkdir -p build make --no-print-directory -C build -f .../Makefile SRC_ROOT=... echo "compiling file2.o" cp .../src/file2.f90 file2.o echo "compiling pgm.o" cp .../src/pgm.f90 pgm.o echo "linking pgm.x" cp pgm.o pgm.x : ``` `make` would recompile both `file2.o`, `pgm.o` and relink `pgm.x`. But in this case it could only relink. So we use the `--touch` feature to indicate that both `file2.o` and `pgm.o` need no recompilation: ``` $ make --touch file2.o pgm.o touch file2.o touch pgm.o touch file2.o touch pgm.o ``` Here is the first indication of the potential issue: the repetition of `touch`. And we see what happened: ``` $ ls Makefile README.md build file2.o pgm.o src target.mk ``` It did touch both `build/file2.o` and `build/pgm.o` since now `make -n` indicates it would only proceed to linking ``` $ make -n [ -d build ] || mkdir -p build make --no-print-directory -C build -f /fs/homeu1/eccc/aq/arqi/mad001/code/makeExpProjects/makeTouchBug/Makefile SRC_ROOT=/fs/homeu1/eccc/aq/arqi/mad001/code/makeExpProjects/makeTouchBug echo "linking pgm.x" cp pgm.o pgm.x : ``` but it also touched two unwanted files in the project root directory. Is there a way to prevent that?
