On Tue, Jan 29, 2008 at 04:10:58PM +0530, Abhishek Sagar wrote: > 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.
A well heeled debugger will necessarily take care of saving contexts (using techniques like setjmp/longjmp, etc) to help it recover from such nested cases (See xmon for example). > I'm assuming that non-kprobe exception notifiers may (or even should) run > after kprobe's notifier callback (kprobe_exceptions_notify). Yes, any such notifier is invoked after kprobe's callback as the kprobe notifier is always registered with the highest priority. > > > 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)) But that still is unneeded dmesg clutter, IMHO. Ananth -- 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/
