libtool 1.5 tag woes

[Paolo Bonzini]

I have just upgraded to libtool 1.5 (Debian's package which is taken out of
CVS) and here are my first experiences.

I'd like to make a custom tag so that, for a particular libtool library, PIC
code is also compiled with -fomit-frame-pointer (I really need the register
that is lost by the GOT code), and that shared libraries are disabled unless
GCC 3.3 or later is found (I also need the visibility attribute to regain
speed accessing global variables).

However, I have had serious problems trying to do this, because there is a
complete dearth of docs about tags.  So far, my only solution has been to
write an Autoconf macro that wraps AC_LIBTOOL_CONFIG with a customizable
preamble: this way, I can put the code to do my custom changes in the
preamble and invoke _LT_AC_LANG_C_CONFIG to create the tag.

An alternative, however, would be to just duplicate the contents of the
default tag into my custom tag, then make the modifications, and then invoke
the standard AC_LIBTOOL_CONFIG.  This however has upward-compatibility
problems in case another configuration variable is added to the tags; is
there a way to copy tags in an upward-compatible way?

Finally, I am quite disgruntled by the 250kb of shell code that is included
in every project even if the CXX/GCJ/F77/RC tags are never used; my solution
has been to redefine AC_LIBTOOL_CXX_CONFIG and friends to a colon, but this
is quite of a hack.  Again I ask if there is a nicer way to strip down my
already huge (750kb) configure script.

WRT the docs, I'd like to understand what part of the tag API is considered
public.  With this information, I may even write down something about it...

Paolo