linux-kernel - Re: [RFC 0/4] arm64: add livepatch support

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Date:	Fri, 24 Apr 2015 17:04:02 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Li Bin <huawei.libin@...wei.com>
CC:	rostedt@...dmis.org, mingo@...nel.org, jpoimboe@...hat.com,
	sjenning@...hat.com, jkosina@...e.cz, vojtech@...e.cz,
	catalin.marinas@....com, will.deacon@....com, broonie@...nel.org,
	live-patching@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 0/4] arm64: add livepatch support

Steve, Li and Masami,

Thank you for all your comments. You pointed out the cases that I didn't think of.
Let me think how I can manage the issues for a while.
Probably I will talk to gcc guys.

-Takahiro AKASHI

On 04/24/2015 03:05 PM, Masami Hiramatsu wrote:
> (2015/04/24 12:24), Li Bin wrote:
>> On 2015/4/24 10:44, AKASHI Takahiro wrote:
>>> This patchset enables livepatch support on arm64.
>>>
>>> Livepatch was merged in v4.0, and allows replacying a function dynamically
>>> based on ftrace framework, but it also requires -mfentry option of gcc.
>>> Currently arm64 gcc doesn't support it, but by adding a helper function to
>>> ftrace, we will be able to support livepatch on arch's which don't support
>>> this option.
>>>
>>
>> This is not correct for the case that the prologue of the old and new function
>> is different.
>
> Hmm, is that possible to support -mfentry on arm64?
>
> Of course we can not call a function directly at the first
> instruction of functions on arm, because it can overwrite
> link register which stores caller address. However, we can
> do "store link register to stack and branch with link"
> on arm. That is actually almost same as -mfentry does :),
> and that may not depend on the prologue.
>
> Thank you,
>
>
>> Thanks,
>> 	Li Bin
>>
>>> I submit this patchset as RFC since I'm not quite sure that I'm doing
>>> in the right way, or we should definitely support -fentry instead.
>>>
>>> Please note that I tested the feature only with livepatch-sample, and
>>> the code for DYNAMIC_TRACE_WITH_REGS is still rough-edged.
>>>
>>> To: Steven Rostedt <rostedt@...dmis.org>
>>> To: Ingo Molnar <mingo@...nel.org>
>>> To: Josh Poimboeuf <jpoimboe@...hat.com>
>>> To: Seth Jennings <sjenning@...hat.com>
>>> To: Jiri Kosina <jkosina@...e.cz>
>>> To: Vojtech Pavlik <vojtech@...e.cz>
>>> To: Catalin Marinas <catalin.marinas@....com>
>>> To: Will Deacon <will.deacon@....com>
>>>
>>> AKASHI Takahiro (4):
>>>    ftrace: add a helper function for livepatch
>>>    livepatch: adjust a patched function's address
>>>    arm64: ftrace: add DYNAMIC_TRACE_WITH_REGS version
>>>    arm64: add livepatch support
>>>
>>>   arch/arm64/Kconfig                 |    4 ++
>>>   arch/arm64/include/asm/ftrace.h    |    4 ++
>>>   arch/arm64/include/asm/livepatch.h |   38 +++++++++++
>>>   arch/arm64/kernel/Makefile         |    1 +
>>>   arch/arm64/kernel/entry-ftrace.S   |  124 ++++++++++++++++++++++++++++++++++++
>>>   arch/arm64/kernel/ftrace.c         |   24 ++++++-
>>>   arch/arm64/kernel/livepatch.c      |   68 ++++++++++++++++++++
>>>   arch/x86/include/asm/livepatch.h   |    5 ++
>>>   include/linux/ftrace.h             |    2 +
>>>   include/linux/livepatch.h          |    2 +
>>>   kernel/livepatch/core.c            |   16 +++--
>>>   kernel/trace/ftrace.c              |   26 ++++++++
>>>   12 files changed, 309 insertions(+), 5 deletions(-)
>>>   create mode 100644 arch/arm64/include/asm/livepatch.h
>>>   create mode 100644 arch/arm64/kernel/livepatch.c
>>>
>>
>>
>>
>
>
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