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SubjectRe: [RFC PATCH 0/5] livepatch: add support on arm64
On 05/30/2015 09:01 AM, Masami Hiramatsu wrote:
> On 2015/05/28 14:51, Li Bin wrote:
>> This patchset propose a method for gcc -mfentry feature(profile
>> before prologue) implementation for arm64, and propose the livepatch
>> implementation for arm64 based on this feature.
>> The gcc implementation about this feature will be post to the gcc
>> community soon.
>>
>> With this -mfentry feature, the entry of each function like:
>>
>> foo:
>> mov x9, x30
>> bl __fentry__
>> mov x30, x9
>> [prologue]
>> ...
>>
>> The x9 is a callee corruptible register, and the __fentry__ function
>> is responsible to protect all registers, so it can be used to protect
>> the x30. And the added two instructions which is register mov operation
>> have ralatively small impact on performance.
>
> Hm, this implementation looks good to me :)
> This also enables us to KPROBES_ON_FTRACE too.

Even if x9 is a callee-saved register, there is no way to restore its original
value in setting up a pt_regs in ftrace_reg_caller.
It's not the right thing for KPROBES_ON_FTRACE, is it?

Saving Link register in stack is not a big deal since the overhead of ftrace
is much bigger.

-Takahiro AKASHI


> Thanks,
>
>>
>> This patchset has been tested on arm64 platform.
>>
>> Li Bin (4):
>> livepatch: ftrace: arm64: Add support for DYNAMIC_FTRACE_WITH_REGS
>> livepatch: ftrace: add ftrace_function_stub_ip function
>> livepatch: ftrace: arm64: Add support for -mfentry on arm64
>> livepatch: arm64: add support for livepatch on arm64
>>
>> Xie XiuQi (1):
>> livepatch: arm64: support relocation in a module
>>
>> arch/arm64/Kconfig | 5 +
>> arch/arm64/include/asm/ftrace.h | 9 +
>> arch/arm64/include/asm/livepatch.h | 45 +++++
>> arch/arm64/kernel/Makefile | 1 +
>> arch/arm64/kernel/arm64ksyms.c | 4 +
>> arch/arm64/kernel/entry-ftrace.S | 154 +++++++++++++++-
>> arch/arm64/kernel/ftrace.c | 28 +++-
>> arch/arm64/kernel/livepatch.c | 41 ++++
>> arch/arm64/kernel/module.c | 355 ++++++++++++++++++------------------
>> include/linux/ftrace.h | 1 +
>> kernel/livepatch/core.c | 17 ++-
>> kernel/trace/ftrace.c | 32 ++++
>> scripts/recordmcount.pl | 2 +-
>> 13 files changed, 508 insertions(+), 186 deletions(-)
>> create mode 100644 arch/arm64/include/asm/livepatch.h
>> create mode 100644 arch/arm64/kernel/livepatch.c
>>
>> --
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>
>


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