Messages in this thread | | | Date | Mon, 18 Sep 2006 19:22:08 +0530 | From | Ananth N Mavinakayanahalli <> | Subject | Re: [patch] kprobes: optimize branch placement |
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On Sun, Sep 17, 2006 at 01:30:38AM +0200, Ingo Molnar wrote: > > * 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.
Also, the hlist->list changes need to be taken care of for the other archs too.
> > 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.
Well, that is the jprobes and return probes case. In the case of normal kprobes, p->pre_handler() should always return 0.
In the case of a jprobe, the setjmp_pre_handler() resets the instruction pointer to the instrumented routine (same signature as the routine being jprobed), which later does a jprobe_return(), a placeholder for the arch-specific trap instruction. We re-enter the kprobe_handler here and then re-enable preemption via the longjmp_break_handler. As for the return probe case, since the underlying instruction originally was a nop (kretprobe_trampoline), we don't need to single-step.
Yes, its a bit convoluted, but we are currently covered for all cases.
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