Messages in this thread | | | Date | Sun, 6 Jan 2002 09:55:49 +0100 | From | Martin Mares <> | Subject | Re: [kbuild-devel] Re: State of the new config & build system |
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Hi Keith,
> That is exactly what kbuild 2.5 does. The slowdown occurs when > massaging the -MD dependencies from absolute names to relative path > names. To support separate source and object trees, renaming of trees, > different names in local and NFS mode etc., the massage code needs a > list of where all the files are before it can convert the absolute > dependencies produced by gcc. Reading and indexing that file for every > compile is _slow_.
I didn't follow the thread from the very beginning nor did I study your makefiles carefully, because I don't have much time for kernel hacking these days, but maybe I won't miss the pond :)
Is there any reason for processing all the files for each compile instead of merging them to a single file once at the start of the make?
I use it in one of my projects, there is the relevant part of the Makefile:
# Black magic with dependencies. It would be more correct to make "depend.new" # a prerequisite for "depend", but "depend.new" often has the same timestamp # as "depend" which would confuse make a lot and either force remaking anyway # or (as in current versions of GNU make) erroneously skipping the remaking.
-include depend
depend: force if [ -s depend.new ] ; then build/mergedeps depend depend.new ; >depend.new ; fi
force:
# Implicit rules
obj/%.o: %.c DEPENDENCIES_OUTPUT="depend.new $@" $(CC) $(CFLAGS) -c -o $@ $<
The DEPENDENCIES_OUTPUT mode is much more convenient than gcc -Mx as it avoids scattering the relevant information over many files. The mergedeps script is a simple Perl script which takes care of merging the dependencies gathered during the previous run of make to the depend file for the next run. It can do a lot of fixups and translations, here is a trivial example:
#!/usr/bin/perl
@ARGV == 2 or die "Usage: mergedeps <base> <update>"; foreach $a (@ARGV) { open F, "$a" or next; $t = ""; while (<F>) { $t .= $_; if (! /\\$/) { ($t =~ /^(.*):/) || die "Parse error at $t"; $rules{$1} = $t; $t = ""; } } close F; } open(F,">" . $ARGV[0]) || die "Unable to write output file"; foreach $a (sort keys %rules) { print F $rules{$a}; } close F;
Have a nice fortnight -- Martin `MJ' Mares <mj@ucw.cz> http://atrey.karlin.mff.cuni.cz/~mj/ Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth Light-year? One-third less calories than a regular year. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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