From mboxrd@z Thu Jan  1 00:00:00 1970
From: Masami Hiramatsu <mhiramat@redhat.com>
Subject: Re: [PATCH -tip v5 2/7] kprobes: checks probe address is instruction  boudary on x86
Date: Mon, 11 May 2009 11:14:36 -0400
Message-ID: <4A0840DC.7080507@redhat.com>
References: <20090509004829.5505.38720.stgit@localhost.localdomain> <20090509004847.5505.37957.stgit@localhost.localdomain> <alpine.DEB.2.00.0905111011060.14976@gandalf.stny.rr.com> <4A083DAD.8000009@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Cc: Ingo Molnar <mingo@elte.hu>, lkml <linux-kernel@vger.kernel.org>,         systemtap <systemtap@sources.redhat.com>, kvm <kvm@vger.kernel.org>,         Ananth N Mavinakayanahalli <ananth@in.ibm.com>,         Jim Keniston <jkenisto@us.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Return-path: <systemtap-return-12301-gls-systemtap=m.gmane.org@sourceware.org>
In-Reply-To: <4A083DAD.8000009@redhat.com>
List-Unsubscribe: <mailto:systemtap-unsubscribe-gls-systemtap=m.gmane.org@sourceware.org>
List-Subscribe: <mailto:systemtap-subscribe@sourceware.org>
List-Post: <mailto:systemtap@sourceware.org>
List-Help: <mailto:systemtap-help@sourceware.org>, <http://sourceware.org/lists.html#faqs>
Sender: systemtap-owner@sourceware.org
List-Id: kvm.vger.kernel.org

Masami Hiramatsu wrote:
>>> +	if (!kallsyms_lookup(paddr, NULL, &offset, NULL, __dummy_buf))
>>> +		return 0;
>>> +
>>> +	/* Decode instructions */
>>> +	addr = paddr - offset;
>>> +	while (addr < paddr) {
>>> +		insn_init_kernel(&insn, (void *)addr);
>>> +		insn_get_opcode(&insn);
>>> +		if (OPCODE1(&insn) == BREAKPOINT_INSTRUCTION) {
>>> +			ret = recover_probed_instruction(buf, addr);
>> Oh, the above puts back the original op code. That is why it is OK?
> 
> Oops, no. I have to use get_kprobe() instead. Thanks!

Ah, I forgot another possibility. There might be another subsystem,
like kgdb, will put their break point on the kernel.
In that case, decoder will decode the instruction is a break point
instruction and the first opcode is int3. So, this part is correct.
In the future, we need to add a generic recover_instruction() code
for those text modification subsystems.

Thank you,
-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com