On 1/29/08, Ananth N Mavinakayanahalli <[EMAIL PROTECTED]> wrote: > > Non kprobe breakpoints in the kernel might lie inside the .kprobes.text > > section. Such breakpoints can easily be identified by in_kprobes_functions > > and can be caught early. These are problematic and a warning should be > > emitted to discourage them (in any rare case, if they actually occur). > > Why? As Masami indicated in an earlier reply, the annotation is to > prevent *only* kprobes.
May be I'm completely off the mark here, but shouldn't a small subset of this section simply be 'breakpoint-free' rather than 'kprobe-free'? Placing a breakpoint on kprobe_handler (say) can loop into a recursive trap without allowing the debugger's notifier chain to be invoked. I'm assuming that non-kprobe exception notifiers may (or even should) run after kprobe's notifier callback (kprobe_exceptions_notify). > > For this, a check can route the trap handling of such breakpoints away from > > kprobe_handler (which ends up calling even more functions marked as > > __kprobes) from inside kprobe_exceptions_notify. > > Well.. we pass on control of a !kprobe breakpoint to the kernel. This is > exactly what permits debuggers like xmon to work fine now. This will still happen. It doesn't stop non-kprobe breakpoints from being handled, wherever they may be. > I don't see any harm in such breakpoints being handled autonomously > without any sort of kprobe influence. Here's what seems to be happening currently: int3 (non-kprobe) -> do_int3 ->kprobe_exceptions_notify -> kprobe_handler (passes the buck to the kernel) -> non-krpobe/debugger exception handler. Here's what the patch will do: int3 (non-kprobe) -> do_int3 ->kprobe_exceptions_notify -> WARN_ON/kprobe_handler -> non-kprobe/debugger exception handler. The WARN_ON (and not a BUG_ON) will be hit iff: (in_kprobes_functions(addr) && !is_jprobe_bkpt(addr)) > Ananth I hope I've understood the point you were making, or at least came close :-). -- Thanks, Abhishek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/