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

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Date:	Fri, 20 Jun 2014 10:37:26 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
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: Re: Re: [RFT PATCH -next v3] [BUGFIX] kprobes: Fix "Failed to
 find blacklist" error on ia64 and ppc64

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".

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

cheers


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