[Gcl-devel] New user question - more explicit information concerning shared library use

[Jordan Rosenthal]

Hi all,

We have a fairly large codebase for image processing that was developed 
on top of an older version of GCL (it is currently running on top of 
2.4.4).  Here's a little bit of info about what we're running

-------
- Linux OS (although we had a version on Solaris)
- GCL 2.4.4
- extensive use of the GCL to TCL/TK 8.4 link
- On top of the TCL/TK we have built the BLT library extension (this 
does not affect the GCL build directly) and a custom TK extension
- Our system loads in a bunch of compiled files on top of GCL and does a 
si::save to create a new image
-------

One of the biggest annoyances I have with our system is that it is 
really painful to use external C and LISP libraries.  For C libraries, 
we have been using the EXTRAS make variable to link in certain symbols, 
but this is not fun to do.  External LISP libraries never seem to work 
out of the box, because most of them are dependent on some of the newer 
ANSI features (e.g., objects don't exists in GCL 2.4.4).

Lo and behold, I've recently out found that newer versions of GCL are 
being worked on by the group reading this email!  It is moving towards 
ANSI compliance and apparently has the ability to link to shared 
libraries with the compiler::link command.  (I have also seen posts 
regarding the gcl-elf-loader that can do this at runtime.)

I downloaded GCL 2.6.6 and have compiled without any (major) issues. 
However, I am having trouble with a few things in the new version:

1) There are a bunch of configure options to get dynamic loading of 
compiled files (e.g., static bfd, local bfd, dynamic bfd, dlopen, etc). 
 Which is the preferred method?  Currently, I am using the dynamic bfd 
(i.e., the shared bfd libraries on my system).  Also, how does the 
gcl-elf-loader fit into the picture?

2) How do I use the compiler::link command?  The syntax is 
straight-forward, but whenever I do it I get errors.  I have tried both 
using and not using the system-p key, but in either case I get some sort 
of error.  In one case (I can't remember which) I get a "cannot 
relocate" error.  In the other case I get a "multiple instances of 
init_code defined" error.

I think my problems most likely stem from a lack of understanding about 
how GCL works internally, especially in regard to dynamic loading of 
object files.  Also, I've only been using LISP (the GCL 2.4.4 variety) 
for a little while now so sometimes that can be a little bit of a block.

If anyone could give me a brief tutorial (or point me to some reading 
material) on how this stuff works, I'd really appreciate it.  I've 
reversed engineered some of the code, but that is slow going and some 
sort of overview would be much appreciated.

Perhaps if it is simpler, we could work with a toy problem.  Let's say I 
have an external shared library...maybe the BLAS numerical library or 
the libxml2 library on Linux.  How do I create an image that let's me 
link to all the symbol's in these (shared) libraries from a clines 
construct later on?

Any help will be much appreciated.

Thanks,

Jordan Rosenthal

PS I also noticed a gcl-users mailing list, but I didn't post there 
because it seems to have very little activity.  If the gcl-devel list is 
not the right place to post this question, just let me know and I'll 
move this discussion to the gcl-users list.