I'm trying to use dlopen() to provide support for loadable modules in
my application. I've got the basic mechanism working with a trivial
shared library that doesn't make any outside calls, but I need to
export some library functions in the main application to make them
available to the run-time loaded modules. And I need to call the
versions in the main app (can't link in separate copies, because
initializations have all ready been done to the libraries inside the
main app).

So far, I'm getting "Exec format errors" on my dlopen calls when I
build a shared library that wants to link to libraries inside the main
app. I assume this means that the linker failed to resolve some stuff.

In order to get the shared library to build, I provided an app.exp file
that listed all the symbols I want to resolve from the main app and
used -bIapp.exp on my link statement. That 'works', but I don't know
if it's the correct way to do it. My main app isn't really a shared
library, and I only know about the .exp file mechanism as it relates to
shared libraries.

I also tried using -bexpall and -brtl on the link statement for my main
app, in case these are needed to get it to support exporting symbols.

Still no luck - and just the Exec format error message to guide me.
So...

1. Is there a more correct way to get my shared library to 'know' about
the symbols it needs from the main app?

2. Is there a way to find out what symbols aren't being resolved at run
time?

3. Am I just doing this completely wrong?

Thanks,
Rob

I seem to be making progress. I moved some stuff from a library I was
statically linking to my shared library directly into the base app
instead. Now my shared library can access that stuff, as well as other
stuff in the base app.

So, it must have been a case of stuff that I thought was in the base
app not really being there. Because I had put it in my app.exp file,
the linker let me build the dynamic module, but dlopen still failed
because of the missing symbols.

Interestingly enough, when I got the missing symbols down to a
manageable level, I started getting meaningful error messages out of
dlerror().

Stuff like:

0509-130 Symbol resolution failed for /u/rob/em/em/emapps/TESTDLL.dll
because:
0509-136 Symbol InitKey (number 6) is not exported from
dependent module x1.
0509-192 Examine .loader secti

which was really helpful. 'dependent module x1' is referring to my
base app (the executable's called x1).

So, it seems like I'm on the right track. Still, if anybody feels like
commenting on

1. whether there's an easier way
2. whether the -bexpall and -brtl options are *really* needed in the
main app and/or the shared library
3. whether an 'exp' file is the correct way to tell the shared library
what functions are available in the main app.

I'd appreciate it.

Thanks,
Rob