From wulf@cip.physik.uni-stuttgart.de Mon May  3 13:51:06 1993
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Date: Fri, 30 Apr 1993 14:49:37 +0100
From: Wulf Hofbauer <wulf@cip.physik.uni-stuttgart.de>
To: hyperc-l@calvin.sfasu.edu
Message-Id: <0096BCEF.234DB820.28270@cip.physik.uni-stuttgart.de>
Subject: object modules&symbol tables
Status: R

Beejay wrote:

>First, I reread the reference on ladd.  All's kosher.  ladd comes with
>the package, I said to myself.  So it must be in libc.  I type at
>the command line: sym -s libc.  When ladd.o comes on the screen, what
>do I see?  A bunch of zeroes for text, data and bss sizes.  Had I
>inadvertently deleted the code somehow?  Let me try the libc that came
>with the fp package.  Same thing!  But as the data for the other
>functions streamed past on the screen, I noticed that ladd.o was not alone.
>There was xprintf.o, setjmp.o, setup.o, alloc.o, sysvars.o, conio.o,
>exec.o, files.o, prtio.o, remove.o, rename.o, strings.o and sync.o -
>all with a zero text size.
[...]
>Out went a help message to the doctor - Andy, that is.   Well, he says,
>ladd and all those other functions apparently missing in libc are opsys
>functions.

You can verify this easily by using "sym libc" (without the -s
parameter). The sym utility lists all references and entry points declared in
an object module, together with a character specifying the symbol type:

T - TEXT entry. Specifies an externally accessible routine/function inside
    of the module.
X - EXTERN. The module refers to this symbol, but it wasn't defined. It must
    be defined inside another module that is linked.
A - ABSOLUTE. The symbol refers to an absolute address. This is the way how
    memory-resident routines are glued to your program.
B - BSS entry. Specifies an uninitialized storage area
D - DATA entry. Specifies an initialized storage area

As you found out, it is perfectly possible for a module to contain neither
coder nor data, but only symbol definitions.

An example:

extern INT printf(); /* creates an EXTERN symbol */
INT main() /* creates a TEXT entry */
{
   ...
}
INT mon() @0xff69; /* creates an ABSOLUTE symbol for address 0xff69 */

INT dummy; /* creates a BSS entry */
INT dummy2=1; /* creates a DATA entry */

Maybe this will clarify some things.

- Wulf

"Though this be madness, there is method in it." (Shakespeare)
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