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Re: Simple "how-to" question, libtool

From: Mar Loh
Subject: Re: Simple "how-to" question, libtool
Date: Fri, 13 Jun 2008 09:34:34 -0500

Brian, thanks very much. Your post was very educational for me! My problem
is mostly solved now (I have everything compiling and going into the right
place, anyway), and I only need to clean up the scripts a bit. My main
problem was realizing that for my situation, it was best to not have a file in every subdirectory, and to just access subdirectories
via's, and just list the Makefile outputs for all subdirectories
in the topsrcdir (even though there are 20 of them).

Ralf, thanks, finally figured that out not 20 minutes before your reply. I
also found that adding the "nobase" prefix such that nobase_include_HEADERS
would preserve the directory structure of the includes.

On Thu, Jun 12, 2008 at 4:10 PM, Brian Dessent <address@hidden> wrote:

> Mar Loh wrote:
> > Q1: Every time I run ./configure from the topdir, the system checks
> > (checking for BSD-compatible....) are re-run every time it gets to a new
> > subdirectory, making the configure take a long time. How do I remove
> these
> > checks when going to a new subdirectory (these are clearly redundant)?
> This is the nature of a recursive build system.  The configure checks
> may seem redundant but they're not, because in such a system each
> directory with a configure script is a separate entity.  If the test was
> not run again, the results would not be available in that dir.  The
> traditional way in a recursive system that a higher level directory
> communicates information to subdirectories is by passing arguments to
> the subconfigure invocations, or invoking submakes with variable
> overrides.
> There is another simpler way, however -- the config cache.  If you
> "configure -C" at the top level, this will create a config.cache file
> there that stores the results of configure tests, or in fact any
> variable matching *_cv_* (for cached value.)  This will also cause
> configure to add "--cache-file=../config.cache" when invoking
> subconfigures.  This causes the subdirs to share the cache.
> A properly written test will do (at least) two things: it will store its
> result in a variable in this *_cv_* namespace, and it will check before
> doing any expensive work whether this variable is already set, and
> bypass the expensive work if so.  The result of this is that a properly
> written test will only do the expensive work once, and any subsequent
> invocations -- either later in that configure script or in a different
> configure script that is sharing the cache -- will just use the cached
> value, normally printing "(cached)" in the output.
> The cache is also useful when configure needs to be re-run, either
> explicitly through the user invoking it or "config.status --recheck", or
> when some dependency gets updated that causes the Makefile to do as
> such.  The second run will use all the cached values for tests that are
> cacheable, usually making it a lot faster.  Of course this is a double
> edged sword: if the user is rerunning configure with significantly
> different options or if the generated configure script has changed
> semantically (e.g. the developer has edited a m4 macro) then the results
> may be intentionally different in which case it would be necessary to
> delete the config.cache file.
> There are some situations where the cache cannot be shared: for example
> if there are two configures that perform a similar test but with
> different options/semantics.  If they both store their result to the
> same variable and are sharing a cache, one will be incorrect.  Also,
> some tests aren't properly written and don't effectively cache their
> result.  But in general I don't think you need to worry unless you're
> doing something really broken in your own macros, as all the ones that
> ship with the tools ought to be cache-friendly.
> There is another, more radical solution: nonrecursive build.  This
> doesn't mean that you have to put everything in one large dir, or even
> that you can't have all the build logic split off into per-directory
> files.  Using includes you can still structure your files as in the case
> of the recursive build, but in this scenario there is only one configure
> script and one large Makefile that handles building everything.
> > Q2: I'd like all *.h files to end up in /topdir/include/, with depth
> (e.g.
> > topdir/libsrcdir/libsrcsubdir1/header1.h -->
> > topdir/include/libsrcsubdir1/header1.h). How do I accomplish this? I've
> > tried some things using top_srcdir, but I think I have the recursion
> messed
> > up such that the local makefiles think that top_srcdir is whatever
> directory
> > it's presently in, if that makes sense.
> What do you mean "end up"?  The result of "make install" should put them
> at their eventual destination on the end user's system, not some
> location in the build dir.  Are you saying that you want the build
> system to create a bunch of symlinks inside the build dir before
> building anything?  What problem are you trying to solve?
> > Q3: I'd like all *.la libraries to end up in /topdir/lib/, without depth
> > (e.g. topdir/lib/
> This goal very much goes against the end-user-centric philosophy that
> the autotools try to foster.  In that vein, the output location is
> whatever the current directory was when the user ran configure.  Also
> called VPATH-builds (after the make feature used to implement it), this
> allows for configuring in a location that is not necessarily the same as
> the source dir.
> This allows for a great deal of flexibility for the end user, such as:
> - For a single source tree, you can have multiple build trees each
> configured with totally different options or even on completely
> different host architectures.
> - The source can reside on a read-only network directory/filesystem and
> still remain buildable.
> - With a build tree separate from the source tree it is easy to simply
> delete everything and start over without having to unpack the source
> again or rely on "make distclean" being usable (e.g. in cases where you
> don't even have a generated Makefile in every dir yet due to configure
> problems.)
> If the user has none of the above needs and simply runs configure in the
> source dir, then the build tree is the same as the source tree as in the
> traditional case.  But it's still important to conceptually think of the
> build tree and the source tree as totally separate, and the resulting
> libs/objects always go in the the build tree, whose location is
> determined by the user.
> I think you will get better help if you state what problem you're trying
> to solve.  The "make install" step will take care of putting the
> libraries where they need to go on the user's system, but that should
> never be a location inside the source or build trees.  If you need to do
> a simulated install for example to create a binary package, the right
> method is "make install DESTDIR=/scratch/dir" which will populate
> everything under /scratch/dir as if it were / of the user's system.  You
> can then create a tarball of that whole tree which captures the
> installed state of everything in your tree.
> Note that automake does have the 'subdir-objects' option.  If you refer
> in a to a source file in a subdirectory foo/bar.c, this
> option tells whether the resulting object from that compilation goes
> into foo/ or ./ in the build tree.  In a nonrecursive build system, this
> allows to control whether you want to collapse the build tree into a
> single flat dir or mirror the same structure as the source tree.  In a
> recursive build system tends to only refer to source files
> in that same dir so it has less of a meaning there.
> Brian

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