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Message-ID: <5566AA4A.4070602@huawei.com>
Date: Thu, 28 May 2015 13:40:26 +0800
From: Li Bin <huawei.libin@...wei.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.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
On 2015/4/24 14:05, 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.
>
Yes, but the method "store link register to stack" will break the arm64 ABI rules,
and memory operations may bring performance cost.
We have a gcc -mfentry implementation strategy for arm64, and based on this we
implement the livepatch for arm64.
I will post the patchset for review soon.
Thank you,
Li Bin
> 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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