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

From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
To: ananth@in.ibm.com
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Tony Luck <tony.luck@gmail.com>,
	Jeremy Fitzhardinge <jeremy@goop.org>,
	linux-ia64@vger.kernel.org, sparse@chrisli.org,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-tip-commits@vger.kernel.org,
	anil.s.keshavamurthy@intel.com, Ingo Molnar <mingo@kernel.org>,
	Fenghua Yu <fenghua.yu@intel.com>, Arnd Bergmann <arnd@arndb.de>,
	Rusty Russell <rusty@rustcorp.com.au>,
	Chris Wright <chrisw@sous-sol.org>,
	yrl.pp-manager.tt@hitachi.com, akataria@vmware.com,
	Tony Luck <tony.luck@intel.com>, Kevin Hao <haokexin@gmail.com>,
	linuxppc-dev@lists.ozlabs.org, rdunlap@infradead.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	dl9pf@gmx.de, Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [RFT PATCH -next ] [BUGFIX] kprobes: Fix "Failed to find blacklist" error on ia64 and ppc64
Date: Thu, 08 May 2014 14:40:00 +0900	[thread overview]
Message-ID: <536B18B0.9060209@hitachi.com> (raw)
In-Reply-To: <20140508044753.GA13413@in.ibm.com>

(2014/05/08 13:47), Ananth N Mavinakayanahalli wrote:
> On Wed, May 07, 2014 at 08:55:51PM +0900, Masami Hiramatsu wrote:
> 
> ...
> 
>> +#if defined(CONFIG_PPC64) && (!defined(_CALL_ELF) || _CALL_ELF == 1)
>> +/*
>> + * On PPC64 ABIv1 the function pointer actually points to the
>> + * function's descriptor. The first entry in the descriptor is the
>> + * address of the function text.
>> + */
>> +#define constant_function_entry(fn)	(((func_descr_t *)(fn))->entry)
>> +#else
>> +#define constant_function_entry(fn)	((unsigned long)(fn))
>> +#endif
>> +
>>  #endif /* __ASSEMBLY__ */
> 
> Hi Masami,
> 
> You could just use ppc_function_entry() instead.

No, I think ppc_function_entry() has two problems (on the latest -next kernel)

At first, that is an inlined functions which is not applied in build time.
Since the NOKPROBE_SYMBOL() is used outside of any functions as like as
EXPORT_SYMBOL(), we can only use preprocessed macros.
Next, on PPC64 ABI*v2*, ppc_function_entry() returns local function entry,
which seems global function entry + 2 insns. I'm not sure about implementation
of the kallsyms on PPC64 ABIv2, but I guess we need global function entry
for kallsyms.

BTW, could you test this patch on the latest -next tree on PPC64 if possible?

Thank you,

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