From: "tiejun.chen" <tiejun.chen@windriver.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [v5][PATCH 2/3] powerpc/kprobe: complete kprobe and migrate exception frame
Date: Mon, 17 Sep 2012 18:19:04 +0800 [thread overview]
Message-ID: <5056F918.9020906@windriver.com> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B6FF1@saturn3.aculab.com>
On 09/17/2012 06:02 PM, David Laight wrote:
>> /* N.B. the only way to get here is from the beq following ret_from_except. */
>> resume_kernel:
>> - /* check current_thread_info->preempt_count */
>> + /* check current_thread_info, _TIF_EMULATE_STACK_STORE */
>> CURRENT_THREAD_INFO(r9, r1)
>> + lwz r8,TI_FLAGS(r9)
>> + andis. r8,r8,_TIF_EMULATE_STACK_STORE@h
>> + beq+ 1f
> ...
>> +1:
>
> Does this add a statically mispredicted branch to every
> return to userspace ?
Return usersapce? No, this is just follow 'resume_kernel'.
Note I add this 'unlikely' here since I assume often Kprobe is always disabled
by default and especially its also rare to kprobe 'stwu' in many kprobe cases.
Tiejun
next prev parent reply other threads:[~2012-09-17 10:19 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-17 9:54 [v5][PATCH 1/3] powerpc/kprobe: introduce a new thread flag Tiejun Chen
2012-09-17 9:54 ` [v5][PATCH 2/3] powerpc/kprobe: complete kprobe and migrate exception frame Tiejun Chen
2012-09-17 10:02 ` David Laight
2012-09-17 10:19 ` tiejun.chen [this message]
2012-09-18 5:05 ` Benjamin Herrenschmidt
2012-09-18 5:09 ` Benjamin Herrenschmidt
2012-09-18 6:13 ` tiejun.chen
2012-09-17 9:54 ` [v5][PATCH 3/3] powerpc/kprobe: don't emulate store when kprobe stwu r1 Tiejun Chen
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