My adventures with `shl_load` on HP-UX 10.20.

I'm trying to get [[BashLoadableBuiltins|bash's loadable functions]] to work on HP-UX 10.20.  But HP-UX 10.20 doesn't have `dlopen` and friends, so I'm trying to get the `shl_load` family to work.  They look superficially similar in nature.  I even managed to hack through all the autoconf stuff, etc. and got it working... sort of.  I can load the `true` and `false` builtins and observe a change in the `help true` output.  But if I attempt to load any of the more complicated builtins -- the ones that actually ''do'' things -- I get unresolved symbols.  It seems an `shl_load`ed library can't resolve symbols that are already part of the running program.

Here is a simple program that loads a "library", in which a function calls something that's already part of the program. This is analogous to what bash is doing with its loadable builtin examples, most of which call internal bash functions.

{{{#!cplusplus
/* foo.c */
#include <stdio.h>
#include <dl.h>

int localfunc(void);

main() {
    shl_t handle;
    int (*rf)(void);

    handle = shl_load ("bar.so", BIND_IMMEDIATE | BIND_VERBOSE, 0L);
    if (handle == NULL) {
	perror ("shl_load bar.so failed");
    	return 1;
    }

    printf ("I am foo\n");

    if (shl_findsym (&handle, "remotefunc", TYPE_UNDEFINED, (void *) &rf)) {
	perror ("shl_findsym remotefunc failed");
	return 1;
    }
}

int localfunc(void) {
    printf ("I am localfunc\n");
    return 0;
}
}}}

And here's the "library" it loads:

{{{#!cplusplus
/* bar.c */
#include <stdio.h>

extern int localfunc(void);

int remotefunc(void) {
    printf ("I am remotefunc\n");
    localfunc();
}
}}}

And here's how I build and run it:

{{{#!nl
imadev:~/tmp$ gcc -c foo.c
imadev:~/tmp$ gcc -c -fpic bar.c
imadev:~/tmp$ ld -b -o bar.so bar.o
imadev:~/tmp$ gcc -o foo foo.o -ldld
imadev:~/tmp$ ./foo
/usr/lib/dld.sl: Unresolved symbol: localfunc (code)  from bar.so
shl_load bar.so failed: Unresolved external
}}}

And this is bash doing the same thing:

{{{#!nl
imadev:/var/tmp/bash-4.0-shl$ enable -f examples/loadables/whoami.so whoami
/usr/lib/dld.sl: Unresolved symbol: loptend (data)  from examples/loadables/whoami.so
/usr/lib/dld.sl: Unresolved symbol: current_user (data)  from examples/loadables/whoami.so
/usr/lib/dld.sl: Unresolved symbol: builtin_usage (code)  from examples/loadables/whoami.so
/usr/lib/dld.sl: Unresolved symbol: reset_internal_getopt (code)  from examples/loadables/whoami.so
/usr/lib/dld.sl: Unresolved symbol: internal_getopt (code)  from examples/loadables/whoami.so
/usr/lib/dld.sl: Unresolved symbol: get_current_user_info (code)  from examples/loadables/whoami.so
bash: enable: cannot open shared object examples/loadables/whoami.so: Unresolved external
}}}

I set up an analogous program using `dlopen` on a Linux box, and that worked (although I had to screw with `LD_LIBRARY_PATH` to make the load work).  I'll omit it for the time being.

TheBonsai tracked down some documentation that explains that you have to supply a linker argument of `-E` on HP-UX to make the main program export local symbols to the dynamically loaded libraries... so let's try that.

{{{#!nl
imadev:~/tmp$ gcc -Wl,-E -o foo foo.o -ldld
imadev:~/tmp$ ./foo
I am foo
I am remotefunc
I am localfunc
}}}

... huh, OK.  Now I guess I get to figure out how to put that into the bash build process.  Maybe by manually setting LDFLAGS during `./configure` I suppose.