[Olsr-dev] Recursive make considered harmful

[John Hay]

On Thu, Nov 20, 2008 at 09:56:05PM +0100, Bernd Petrovitsch wrote:
> Hi!
> 
> Most probably know the subjectalready (and the writings on
> http://miller.emu.id.au/pmiller/books/rmch/).
> 
> That is the first version to kill recursive make calls (read: no more
> `make -C` somewhere somehow):
> http://bernd.petrovitsch.priv.at/olsr-ng/recursive-make-considered-harmful-v1.patch
> against http://gredler.at/hg/olsrd as of now (beware it's 70KB or so).
> What is done/how does it work:
> - each subdirectory which has now a Makefile (read:
> src/{cfgparser,olsr_switch}, lib*) gets local.mk containing the build
> info for that directory.
> - these local.mk are included in the main Makefile.
> - these local.mk defines targets, dependencies etc. similar to now.
> 
> Gains:
> - the build time on my Via-C3 is roughly halved (using ccache in both
>   cases of course) - we save a dozen fork(2)+exec(2) of the sub-makes,
>   they needn't parse Makefile.inc again, etc. (and the output of a `make
>   build_all` is smaller).
> - src/cfgparser build is much cleaner and simpler.
> - make `install_all` is *much* faster since we don't call ldconfig for
>   each plugin but once at the end.
> The question is more if the ldconfig is necessary - ATM one (at /me does
> it) can install the plugins anywhere and olsrd finds it withoput
> LD_LIBRARY_PATH, /etc/ld.so.conf, or similar if the PREFIX and DESTDIR
> is used correctly (identical to autotools).
> - I actually regression-tested the new and old dependencies: Just do
> `make clean_all && make build_all >build-clean 2>&1 && for f in Makefile
> Makefile.inc */*/local.mk; do touch "$f"; make build_all
> >build-${f//\//-}" 2>&1"; done` and (tk)diff build-clean against the
> others.
> 
> The main difference to the current `make -C` way is IMHO that the
> subdirectory's name must be present on the .o/.c/.h/.d/... files as the
> (only) `make` call never chdir(2)s (unless someone adds a `cd` to some
> target).
> Other differences:
> - the MAKEBIN and (presently unused) MAKELIB make variable vanish. The
>   main() function for the cfgparser binary is moved into a separate .c
>   file. That makes life much simpler and easier (and it is quite crufty
>   right now).
> - since we have one `make` in one directory, no more TOPDIR or similar
>   variables
> 
> That patch is not final as
> - all lines with "#dbg" will be removed - these are the old ones.
> - I intend to/propose to/would simply delete all the now superfluous
>   Makefiles. Otherwise one has to fix them (or keep the duplicated build
>   info).
> - and a few simplifications more are possible afterwards (but would
>   disturb `hg fetch` right now too much if someone fixes some build
>   issue)
> 
> And now the real hacky stuff[0] possibly creating the usual porting
> problem:
> Since the build for the plugins is pretty identical, we use Makefile
> magic which reduce the plugins local.mk to one line (not counting
> comments) which generates variables, targets and dependencies in a way
> that can use them like normal handcoded Makefiles.
> If you want to see what really is generated, duplicate the line in a
> plugins local.mk, replace the "eval" with "error" or"warning" and find
> the output.
> 
> lib/httpinfo/local.mk is not so trivial so one can see that that
> approach doesn't impose any limit.
> The main question is if that builds on the more obscure[1]
> non-GNU-systems like OpenBSD or MacOS. I have no idea (and no
> possibility to try/check) what the `make` there can do or not.
> 
> The patch should be applicable with `-p1`.
> If you dare try it (please do!;-), please tell me if it works or not
> (and where). And for error reports, please attach *all* of the output
> and mail it or put it somewhere to download.
> 
> 	Bernd
> 
> [0]: There *is* much more in `make` then just variables and dependency
>      rules;-)
> [1]: Don't take it personal. I just can't think of a better word right
>      now.

Ghmf, you do not even mention FreeBSD... :-) I have applied your v2
patch and the result is short:

###########################################
dolphin:~/olsrd-666eba3a65c0 > gmake build_all
lib/bmf/local.mk:41: *** "*** BMF Plugin only supported on Linux, sorry!".  Stop.
dolphin:~/olsrd-666eba3a65c0 > gmake
lib/bmf/local.mk:41: *** "*** BMF Plugin only supported on Linux, sorry!".  Stop.
dolphin:~/olsrd-666eba3a65c0 > gmake all
lib/bmf/local.mk:41: *** "*** BMF Plugin only supported on Linux, sorry!".  Stop.
dolphin:~/olsrd-666eba3a65c0 >
###########################################

John
-- 
John Hay -- (spam-protected) / (spam-protected)