cvs commit: src/sys/net if_vlan.c

Marcel Moolenaar marcel at
Fri Aug 4 20:02:16 UTC 2006

On Fri, Aug 04, 2006 at 01:14:22PM -0400, John Baldwin wrote:
> > 
> > So, putting the kdb_backtrace() under KDB is not a matter of said
> > function not being present without KDB, it's that we don't want
> > to emit backtraces when debugging is not enabled. Backtraces are
> > a debugging tool and it makes sense to emit them only when the
> > kernel is configured for debugging.
> In practice this ends up being redundant though as to have kdb_backtrace() 
> actually do anything you have to have DDB in your kernel config, which 
> requires KDB.

That's really an implementation detail. What if we get a new debugger
backend that allows backtraces? What if the GDB backend is extended to
allow backtraces?

The point is that kdb_backtrace() is there if you want a backtrace and
you call it based on whatever option that makes sense at the call-site
or even unconditionally if that's the right thing.
Whether there's actually a backend that can make a backtrace is really
a seperate issue. We just happen to implement backtracing and unwinding
by debuggers, but with an unwinder in the kernel on ia64, we really
don't need a debugger in order to make a backtrace and it's not that
unrealistic that I create a backend that can only do backtraces...

> Places that call kdb_enter() aren't all #ifdef KDB IIRC.  It's 
> just a feature that kdb_foo() functions become NOPs when the kernel isn't 
> configured for debugging, so I think the #ifdef KDB's would be redundant.

None of the kdb_*() functions in src/sys/kern/subr_kdb.c turn into
NOPs when option KDB is not present. They are all unconditionally
functional by design and should therefore be called conditionally
by consequence.

 Marcel Moolenaar	  USPA: A-39004		 marcel at

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