Re: [patch] kprobes: optimize branch placement

Ingo Molnar
2006-09-16T23:38:42Z

* Andrew Morton <akpm@osdl.org> wrote:

> On Sat, 16 Sep 2006 22:43:42 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
>
> > --- linux.orig/arch/i386/kernel/kprobes.c
> > +++ linux/arch/i386/kernel/kprobes.c
> > @@ -354,9 +354,8 @@ no_kprobe:
> > */
> > fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
> > {
> > - struct kretprobe_instance *ri = NULL;
> > - struct hlist_head *head;
> > - struct hlist_node *node, *tmp;
> > + struct kretprobe_instance *ri = NULL, *tmp;
> > + struct list_head *head;
> > unsigned long flags, orig_ret_address = 0;
> > unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
>
> Wanna fix the whitespace wreckage while you're there??

will do. If you consider this for -mm then there's some djprobes noise
in the patch [djprobes isnt upstream yet] - it's not completely
sanitized yet. (but it should actually work if applied to upstream -
kprobes and djprobes are disjunct.) Also, i havent tested with
CONFIG_KPROBES turned off, etc. I'll do a clean queue.

> i386's kprobe_handler() appears to forget to reenable preemption in
> the if (p->pre_handler && p->pre_handler(p, regs)) case?

that portion seems a bit tricky - i think what happens is that the
pre_handler() sets stuff up for single-stepping, and then we do this
recursive single-stepping (during which preemption remains disabled),
and _then_ do we re-enable preemption.

Ingo