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SubjectRe: [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@goodmis.org>
>>> To: Ingo Molnar <mingo@kernel.org>
>>> To: Josh Poimboeuf <jpoimboe@redhat.com>
>>> To: Seth Jennings <sjenning@redhat.com>
>>> To: Jiri Kosina <jkosina@suse.cz>
>>> To: Vojtech Pavlik <vojtech@suse.cz>
>>> To: Catalin Marinas <catalin.marinas@arm.com>
>>> To: Will Deacon <will.deacon@arm.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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