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Date: Tue, 5 Nov 2013 17:41:02 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, Namhyung Kim <namhyung.kim@lge.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Hyeoncheol Lee <cheol.lee@lge.com>,
        Hemant Kumar <hkshaw@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        "zhangwei(Jovi)" <jovi.zhangwei@huawei.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Subject: Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch
	methods (v6)
Message-ID: <20131105164102.GC2460@redhat.com>
References: <1383029621-7384-1-git-send-email-namhyung@kernel.org> <20131102155458.GA6981@redhat.com> <87ob60366m.fsf@sejong.aot.lge.com> <87fvrc35kj.fsf@sejong.aot.lge.com> <20131104155131.GD4440@redhat.com> <20131104162229.GA8921@redhat.com> <20131104184741.GA15945@redhat.com> <20131104185754.GA16428@redhat.com> <8761s71rxw.fsf@sejong.aot.lge.com>
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On 11/05, Namhyung Kim wrote:
>
> On Mon, 4 Nov 2013 19:57:54 +0100, Oleg Nesterov wrote:
> >>
> >> 	static void __user *get_user_vaddr(struct pt_regs *regs, unsigned long addr)
> >> 	{
> >> 		return (void __force __user *)addr + instruction_pointer(regs);
> >> 	}
> >>
> >> ?
> >>
> >> This should solve the problems with relocations/randomization/bss.
> >>
> >> The obvious disadvantage is that it is not easy to calculate the
> >> offset we need to pass as an argument, it depends on the probed
> >> function.
> >
> > forgot to mention... and instruction_pointer() can't work in ret-probe,
> > we need to pass the "unsigned long func" arg somehow...
>
> Hmm.. what's the value of tu->offset in this case?  Does it have the
> offset of the return address or the start of the function?

It is the offest of function. IOW, it is the same regardless of
is_ret_probe().

Ignoring probes_seq_show() we only need it for uprobe_register().

(yes, it is also used in uprobe_unregister/apply, but this is only
 because this API ugly and should be cleanuped).

Oleg.