linux-kernel - Re: [RFT PATCH -next v3] [BUGFIX] kprobes: Fix "Failed to find blacklist" error on ia64 and ppc64

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Message-ID: <53A398BB.2010909@hitachi.com>
Date:	Fri, 20 Jun 2014 11:13:15 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	"Suzuki K. Poulose" <suzuki@...ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tony Luck <tony.luck@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-ia64@...r.kernel.org, sparse@...isli.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-tip-commits@...r.kernel.org, anil.s.keshavamurthy@...el.com,
	Ingo Molnar <mingo@...nel.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Arnd Bergmann <arnd@...db.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Chris Wright <chrisw@...s-sol.org>,
	yrl.pp-manager.tt@...achi.com, akataria@...are.com,
	Tony Luck <tony.luck@...el.com>,
	Kevin Hao <haokexin@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	rdunlap@...radead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dl9pf@....de, Andrew Morton <akpm@...ux-foundation.org>,
	linuxppc-dev@...ts.ozlabs.org,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [RFT PATCH -next v3] [BUGFIX] kprobes: Fix "Failed to find blacklist"
 error on ia64 and ppc64

(2014/06/20 9:37), Michael Ellerman wrote:
> On Thu, 2014-06-19 at 20:20 +0900, Masami Hiramatsu wrote:
>> (2014/06/19 20:01), Masami Hiramatsu wrote:
>>
>>>>>>> Ah, those messages should be shown in dmesg when booting if it doesn't work,
>>>>>>> because the messages are printed by initialization process of kprobe blacklist.
>>>>>>> So, reproducing it is just enabling CONFIG_KPROBES and boot it.
>>>>>> Well,  we don't get those messages on Power, since the kallsyms has the
>>>>>> entries for ".function_name". The correct way to verify is, either  :
>>>>>
>>>>> Hmm, that seems another issue on powerpc. Is that expected(and designed)
>>>>> behavior?
>>>> AFAIK, yes, it is.
>>>> To be more precise :
>>>>
>>>> we have 'foo' and '.foo' for a function foo(), where 'foo' points to the
>>>> function_entry and '.foo' points to the actual function.
>>>
>>> Ah, I see. So if we run
>>>
>>>   func_ptr p = foo;
>>>   return p == kallsyms_lookup_name(".foo");
>>>
>>> it returns true.
>>
>> One more thing I should know, is the address of ".function_name" within the
>> kernel text? In other words, does kernel_text_address() return true for that
>> address? If not, it's easy to verify the address.
> 
> Yes. That is the text address, kernel_text_address() should definitely return
> true.
> 
> On 64-bit, ABIv1, "foo" points to the function descriptor, in the ".opd"
> section.
> 
> ".foo" points to the actual text of the function, in ".text".

Hmm, I misunderstood that. Anyway, we can verify it by kernel_text_address().

> 
> On 64-bit, ABIv2, "foo" points to the text in ".text". There are no dot
> symbols.

OK, in that case, kernel_text_address() check is still available. :)

Thank you,


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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