Tim Murphy wrote: > I think that checksumming might benefit some targets. It would be > nice to be able to implement different "methods" for different targets > - because not all methods work well in all circumstances.
> I have one example where every single file in a huge build includes 1 > particular header file. The file defines macros which are the > features that are enabled or disabled in the build. > > We know which features are used by particular components so in theory > we could work out not to rebuild components that are not influenced by > what's happened to the header file. e.g. we could switch on a feature > or add a new feature without forcing a rebuild of the entire source > base. You can do that already today by simply splitting your global feature header file into smaller pieces and letting targets depend on only the relevant pieces rather than everything... Of course that means you have to know which targets need which pieces of the feature set to define the correct dependencies but that's the price you pay for properly functioning incremental rebuilds. You can't have your cake and eat it too... This sort dependency generation can usually be automated fairly easily though, but it's something that is highly dependant on your software architecture, build structure, programming language, etc... For that reason it belongs in your makefiles and not in GNU make itself... > This requires something like md5 but also some kind of "filter" to > determine what kinds of changes are significant to the particular > target that you are testing the dependency for IMNSHO, this is not a problem that make can (or should even attempt to) solve for you. This "filter" as you call it would have to know a lot about the the syntax your header and code files which makes it a bad candidate for a core make feature. This is the classic "global.h" problem of large software builds... > You can emulate md5 checksum dependencies in make of course, using > temporary marker files, but it's a bit ugly and complicated.. This problem is not strictly related to MD5 summing. With MD5 summing instead of timestamps, your global header file would still change and cause a full rebuild because this is what you explicitly asked for by saying that all targets depend on it. /Lasse _______________________________________________ Bug-make mailing list Bug-make@gnu.org http://lists.gnu.org/mailman/listinfo/bug-make
