Hello Dan, On Fri, Jun 03, 2005 at 03:15:50PM -0400, Dan Manthey wrote: > One of the last steps that ./config.status does when making config.h is to > check whether the newly generated file differs from that being replaced, > and if it does not, the old one is not overwritten. This is done to > reduce unnessary rebuilding of source dependented on config.h. This I > understand. > > But the similar check for non-modification of generated makefiles is > commented out in status.m4. Why is this? There's a crypic "This would > break Makefile dependencies." in the comment, but I don't understand how. > Could someone enlighten me? Not only generated makefiles; this hold for generated files in general. The makefile has a rule which says how to refresh those files; roughly: Makefile: Makefile.in ./config.status ./config.status Makefile foo: foo.in1 foo.in2 ./config.status ./config.status foo If config.status wouldn't touch the output file, the rule would be triggered each time make is invoked. That would slow down things. config.h is worth a special treatment, as lot of files depend on it. But Automake has a lot of work with this, see an Automake-generated Makefile in a directory with a config.h. There cannot be the dependency config.h: config.h.in Instead, there is a rule for stamp-h1,... Please also note that the code in status.m4 for CONFIG_FILES code contains a hook which is used by Automake to create the stamp-h1 file. Without this the makefile would ignore the config.h created by configure and would call config.status to re-create it. As I said, this is still worth it for config.h. But you don't want to repeat this for other generated files. A final remark: autoheader doesn't update config.h.in if it doesn't change. But the Automake-generated rule does "touch config.h.in". (The other possibility would be to use a stamp file---but that would be too complicated.) So Automake effectively cancels this feature of autoheader. You might ask why autoheader has this feature; well perhaps someone, in a distant galaxy, might be using it... It's not worth any effort. (You can occassionally see a spare run of autoheader if you ran autoheader manually before make.) Hope this explains it, Stepan _______________________________________________ Autoconf mailing list Autoconf@xxxxxxx http://lists.gnu.org/mailman/listinfo/autoconf
