------- Robert Jørgensgaard Engdahl Cum Laude MSc. C.S. SW-Developer, R&D Video Services & Applications
Bang & Olufsen A/S Peter Bangs Vej 15 DK-7600 Struer Denmark Phone: (+45) 96 84 44 05 Internal phone: 454405 e-mail: r...@bang-olufsen.dk Location: Factory 1 - West Philip Guenther <guent...@gmail.com> wrote on 29-04-2010 19:26:40: > On Thu, Apr 29, 2010 at 3:59 AM, Edward Welbourne <e...@opera.com> wrote: > >> Delete a "clean-depend" rule on sight, > > > > I cannot agree. > > If I write a rule to make something, I also write a rule to get rid of > > it. It's just basic hygiene ... > > I propose the following guideline: If you have a target that generates > A (and B as a side-effect), then a 'clean*' rule that deletes B should > also delete A (and vice versa). > > So, I do have a rule to delete *.d files, it's called "clean". Since > I don't have rules for building .d files other than with .o files, it > Just Works. > > > >> or rename it to the more accurate "break-future-builds". > > > > If you have a sensible rule to generate .d files when needed, you > > haven't broken your builds - you've just obliged yourself to > > regenerate .d files. Which may be wasteful, but see below. > > Okay, so if you have a rule to delete .d files without deleting .o > files, you need rules to build .d files. In my experience, the only > reason to have *either* of those is "because that's how the Makefile > was originally written and the current behavior doesn't hurt enough > for me to spend the time to fix it". > > > ... > > Speaking of the subtleties of dependency tracking: do an update in > > your version control system, watch some header go away - and all files > > that used to reference it drop those references. Your .d files claim > > a bunch of stuff depends on this missing file; but you have no rule to > > regenerate it. So make will not even try to compile anything (even > > though everything *would* compile fine) because your .d file say that > > all the .o files that need recompiled depend on a file that doesn't > > exist any more; make clean-depend fixes that. > > The fix for that has been documented for years on Paul's webpage, and > is most easily done now with gcc's -MP option. > This is also kind of the solution I would have used (kinda, as I would just have made a %.h rule), but then the gcc manual is a bit confusing, as it mentions phony targets (which would really break the idea of incremental builds), but I see that the targets are only phony in the English sense, and not in the GNU Make sense (.PHONY). > > > If generating .d as a side-effect, don't listen to the manual's advice > > that says you need to sed its content to claim that the .d depends on > > the same things the .o does. If those things have changed, the .o > > shall be regenerated and hence so shall the .d; and you don't need > > this updated version of the .d file to discover that the .o needs > > rebuilt. Changes to .h files consequently never trigger re-exec. > > Ah, it looks like your comments are addressed at just what's in the > GNU make info pages and not the advanced method on Paul's webpage. I > agree that what's in the info pages has many of the problems you > mention...which is why this thread is about updating what's there. > > > Philip Guenther >
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