Re: Partial autoconf transition thoughts

["Maciej W. Rozycki" <macro@ds2.pg.gda.pl>]

On 13 Jun 2003, Alexandre Oliva wrote:

> >> >  OK, the first is a native one, so it goes to $exec_prefix, say: 
> >> > /usr/lib.  The second one is a cross one, so it goes to
> >> > $exec_prefix/$target_alias, say: /usr/mipsel-linux/lib.  Finally, the last
> >> > one is a cross one, too, so it goes to $exec_prefix/$target_alias, say:
> >> > /usr/mipsel-linux/lib -- oops! -- the second one just got overwritten... 
> >> 
> >> Two crosses to the same target, and you don't want one to overwrite
> 
> >  ... from different hosts; only the build is the same.
> 
> If it's for different hosts, then you also clobbered all binaries that
> you'd installed in the same exec_prefix.  Which is why in this case
> you'd be better off using per-host exec_prefixes.  That's exactly the
> purpose behind the distinction between prefix and exec_prefix.  Files
> in prefix are host-independent, whereas those in exec_prefix are
> host-specific.

 I smell a confusion here.  My setup is essentially as follows:

1. I keep architecture-independent data in $prefix.

2. I keep build-specific data in $exec_prefix.

3. I keep host-specific data in $exec_prefix/$host_alias.

4. I keep target-specific data in $exec_prefix/$target_alias.

Except from host-specific libraries that recognize a different target
there is no conflict, as 3. above only contains libraries and headers (in
lib and include subdirectories, respectively) and 4. above only contains
executables (in a bin subdirectory).  It seems to be the preferred setup
now as cross-tools get installed there by default (with
$target_alias-<name> aliases also installed in $exec_prefix/bin) and they
look for libraries and headers there by default, too.

> >  It looks sane to me, but I think both host-x-target (or really
> > build-x-target; what about build-x-host-x-target? ;-) )
> 
> build is irrelevant at install time.  If some package installs
> binaries for the build machine, the package is broken.

 It's not relevant then indeed, but once run it's relevant again as you --
essentially when doing a compilation you run binaries/libraries for the
build system, use headers and link against libraries for a host system and
these headers and libraries can support yet another target system (not
necessarily different from the build one).  You can legitimately have a
mipsel-linux host bfd library supporting the alpha-linux target installed
on an i386-linux system and use that library for linking binaries to be
run on a mipsel-linux host. 

> > libraries and such binaries should both be under
> > $exec_prefix/x-$target_alias for consistency then.
> 
> Nope.  $exec_prefix/x-$target_alias would hold libraries containing
> code that runs on the host (so exec_prefix, not host-independent
> prefix), used to manipulate binaries in the target's format
> (e.g. host-x-target libbfd).  Compare this with binaries and libraries
> in the target's format, that we currently install in
> $exec_prefix/$target_alias, even though they aren't host-specific in
> any way, and therefore they could legitimately be installed in
> $prefix/$target_alias.  The fact that they were build on a certain
> host should be irrelevant.

 I mean binaries for a given target and libraries/headers for the very
same host should be in the same directory tree.  Native libraries (i.e. 
for the build) supporting the target (where target != build) should be
elsewhere as they conflict with the respective libraries for the same host
(whether their host == build or not).  Native libraries supporting the
build (which target == host == build) are in $exec_prefix.

> > And host libraries (I suppose you mean that -- few libraries, such
> > as bfd, actually recognize the existence of a target; I understand the
> > naming can be confusing) may go to $prefix/$host_alias
> 
> Host libraries *have* to be in $exec_prefix, and $host_alias is
> therefore redundant.

 Host libraries must not be in $exec_prefix unless host == build.  You
cannot run a library that is for a different host.

> > (where $prefix may sometimes effectively be equal to $exec_prefix)
> 
> If you use the same exec_prefix for different hosts, you're already
> toast.  Get used to --exec-prefix=${prefix}/H-${host_alias} before
> it's too late :-)

 I'm not near being toast at all and I use this setup successfully for
about four years now.  There is a lot of confusion in understanding what
is build, host and target (e.g. rpm uses a --target option for what is
named --host in autoconf) and I had troubles in the beginning, too.  Not
anymore.  If still in doubt please feel free to visit my FTP site
(ftp://ftp.ds2.pg.gda.pl/pub/macro) and see how various bits are laid out
in my binary RPM packages.  They do work and there are no conflicts. 

  Maciej

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +