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

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Date:	Fri, 24 Apr 2015 15:05:31 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Li Bin <huawei.libin@...wei.com>
CC:	AKASHI Takahiro <takahiro.akashi@...aro.org>, 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

(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
>>
> 
> 
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com


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