Not All Symbols Present in a Loadable Kernel Module

[Alexander Sack]

For my own edification, unless you specifically mark a function
inline, will gcc really optimize them out?  That seems a little
overboard unless there is some compiler option that says its okay to
do that.  I guess that would be very easy to test if you do as you
say, just sock away the function address pointer somewhere and you
should be okay...

-aps

On Mon, May 5, 2008 at 12:32 PM, Kostik Belousov <kostikbel at gmail.com> wrote:
>
> 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.
>