dynamic library problem (shl_load)

[Ulrich Deiters]

Condider the following case:
file1.c contains the main program and
some subroutines. file2.c contains subroutines only, which need to go into a shared library. I compile like this:
cc -Aa -c +z -g file2.c
ld -b -o libxyz.sl file2.o
cc -Aa -g file1.c -ldld
The mainprogram loads libxyz by means of shl_load.
If I run a.out and file2.c contains external variables (extern int something ...), the shl_findsym fails. Without external variables the subroutines from file2 are loaded correctly - but then it is not possible to invoke a subroutine from file1 any longer (dld error).

The dlopen method works, but that is not available on my system (HP-UX 10.20).

Any ideas what went wrong?

[Manish Srivastava]

Hi,

Could you give the dld error message.

manish

[Ulrich Deiters]

... something like "dld error, symbol not found.

This is funny, because the missing subroutine had been linked statically.

[Mike Stroyan · Accepted solution]

A declaration like
extern int my_symbol;
does not allocate any storage for "my_symbol".
If you want the shared library to provide a
symbol you need to declare it as
int my_symbol;
somewhere in the shared library.

If you meant to declare a symbol in the a.out
and access it from the shared library, then
you may need to add a -Wl,-E option when
linking the a.out. That tells ld to export
all symbols for use by shared libraries even
if they are not used by code in the a.out
itself.

[Ulrich Deiters]

The exact error message was
"/usr/lib/dld.sl: Unresolved symbol: parse_global (code) from /home/ukd/architex
/lib/libbibliography.sl",
where parse_global() is a statically linked
subroutine (or rather, it is compiled together with main()).

I do not quite understand why the program forgets its static subroutine table. But whatever the reason is,"-Wl,-E" did the trick! Thank you for your help.

[ranganath ramachandra]

by default, symbols are not exported from the application program ('a.out') unless they are being imported by a shared library seen at link-time (not one that may dynamically loaded by the user). so in your case the precise solution is to add this to your compile line : '-Wl,+ee,parse_global'

the -E flag makes the linker export all symbols from a.out, that is how it fixed your problem.