linux-kernel - Re: [patch] kprobes: optimize branch placement

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Message-ID: <20060916233038.GC23132@elte.hu>
Date:	Sun, 17 Sep 2006 01:30:38 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Jes Sorensen <jes@....com>,
	Roman Zippel <zippel@...ux-m68k.org>, tglx@...utronix.de,
	karim@...rsys.com, Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Tom Zanussi <zanussi@...ibm.com>, ltt-dev@...fik.org,
	Michel Dagenais <michel.dagenais@...ymtl.ca>, fche@...hat.com
Subject: Re: [patch] kprobes: optimize branch placement


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

> On Sat, 16 Sep 2006 22:43:42 +0200
> Ingo Molnar <mingo@...e.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
-
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