Not All Symbols Present in a Loadable Kernel Module

[Kostik Belousov]

On Mon, May 05, 2008 at 09:27:10AM -0700, David Christensen wrote:
> > >  Yes, I'm building a debug kernel.  I have the line listed above as
> > well
> > >  as the following:
> > >
> > >  options KDB
> > >  options DDB
> > >  options GDB
> > >  options INVARIANTS
> > >  options INVARIANT_SUPPORT
> > >  options WITNESS
> > >  options WITNESS_SKIPSPIN
> >
> > Dave:
> >
> > What symbols can you not access exactly and how are you
> > installing/setting up debugging?
> >
> > I just built a RELENG_7 with DDB and I'm able to access bce symbols
> > without a problem.  I can examine them and call them.  I'm not using
> > options GDB however, only KDB/DDB.
> >
> > I would:
> >
> > - Make sure you have the right if_bce.ko/if_bce.ko.symbols files
> > generated/installed which contains the debug sections of your ko (from
> > the objcopy calls during the build - the binary is stripped with a
> > section pointer to the if_bce.ko.symbols file for debugging
> > information I believe)
> > - If you are using GDB, make sure its pointed to the right source base
> > so it can retrieve symbol information correctly
> > - If you are using GDB, stub it out and just use DDB to verify that
> > your build is sane (it works for me!)
> > - If all else fails, you can always build bce statically (just to move
> > forward etc.)
> 
> - Enable the kernel debugger as described above
> - Build the driver in the /usr/src/sys/modules/bce directory with the
>   command "make".
> - Run the command "nm if_bce.ko | grep dump_stat" in the same directory
>   with the kernel module just built.
> 
> In my case I only see a symbol for bce_dump_status_block, but there is a
> second routine called bce_dump_stats_block.  In my working build there
> are 23 functions that start with "bce_dump" but only 8 are displayed with
> the command "nm if_bce.ko | grep bce_dump".  Of course, I also get the
> symbol not present error when I try to use any of those missing symbols
> through a "call" command in the debugger.

Most likely, they are optimized out, gcc likes to inline once-called
static functions. Aside from playing with the optimization options,
the easiest way seems to use functions somewhere else, e.g., put the
addresses into some table. Just guessing.
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