linux-kernel - Re: [PATCH v15 04/10] arm64: Kprobes with single stepping support

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Date:	Tue, 9 Aug 2016 07:49:40 +0900
From:	Masami Hiramatsu <mhiramat@...nel.org>
To:	David Long <dave.long@...aro.org>
Cc:	Daniel Thompson <daniel.thompson@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Rutland <mark.rutland@....com>,
	Yang Shi <yang.shi@...aro.org>,
	Zi Shen Lim <zlim.lnx@...il.com>,
	Will Deacon <will.deacon@....com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	yalin wang <yalin.wang2010@...il.com>,
	Li Bin <huawei.libin@...wei.com>,
	Jisheng Zhang <jszhang@...vell.com>,
	John Blackwood <john.blackwood@...r.com>,
	Pratyush Anand <panand@...hat.com>,
	Huang Shijie <shijie.huang@....com>,
	Dave P Martin <Dave.Martin@....com>,
	Petr Mladek <pmladek@...e.com>,
	Vladimir Murzin <Vladimir.Murzin@....com>,
	Steve Capper <steve.capper@...aro.org>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Mark Brown <broonie@...nel.org>,
	Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
	William Cohen <wcohen@...hat.com>,
	Alex Bennée <alex.bennee@...aro.org>,
	Adam Buchbinder <adam.buchbinder@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	linux-kernel@...r.kernel.org, James Morse <james.morse@....com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robin Murphy <robin.murphy@....com>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	sparclinux <sparclinux@...r.kernel.org>
Subject: Re: [PATCH v15 04/10] arm64: Kprobes with single stepping support

On Mon, 8 Aug 2016 10:29:05 -0400
David Long <dave.long@...aro.org> wrote:

> >> @@ -489,20 +477,15 @@ int __kprobes setjmp_pre_handler(struct kprobe
> >> *p, struct pt_regs *regs)
> >>  {
> >>      struct jprobe *jp = container_of(p, struct jprobe, kp);
> >>      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> >> -    long stack_ptr = kernel_stack_pointer(regs);
> >>
> >>      kcb->jprobe_saved_regs = *regs;
> >>      /*
> >> -     * As Linus pointed out, gcc assumes that the callee
> >> -     * owns the argument space and could overwrite it, e.g.
> >> -     * tailcall optimization. So, to be absolutely safe
> >> -     * we also save and restore enough stack bytes to cover
> >> -     * the argument area.
> >> +     * Since we can't be sure where in the stack frame "stacked"
> >> +     * pass-by-value arguments are stored we just don't try to
> >> +     * duplicate any of the stack.
> >  > ...
> >>                                       Do not use jprobes on functions
> >> that
> >> +     * use more than 64 bytes (after padding each to an 8 byte boundary)
> >> +     * of arguments, or pass individual arguments larger than 16 bytes.
> >
> > I like this wording. So much so that it really would be great to repeat
> > this in the Documentation/. Could this be included in the list of
> > architecture support/restrictions?
> >
> 
> Are you thinking specifically of the "5. Kprobes Features and 
> Limitations" section in Documentation/kprobes.txt?

OK, That's a good idea :)

If you update the patch for that, please feel free to add my Ack.

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>