[RFC PATCH 0/5] livepatch: add support on arm64
huawei.libin at huawei.com
Tue Jun 2 04:00:13 PDT 2015
On 2015/6/2 10:15, AKASHI Takahiro wrote:
> 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:
>>> mov x9, x30
>>> bl __fentry__
>>> mov x30, x9
>>> 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.
Hi, Takahiro AKASHI
Firstly, x9 is not a callee-saved but a caller-saved register(or being called
Secondly, I think x9 is already protected properly, please reference the patch:
[PATCH 1/5] livepatch: ftrace: arm64: Add support for DYNAMIC_FTRACE_WITH_REGS
[PATCH 3/5] livepatch: ftrace: arm64: Add support for -mfentry on arm64
> 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.
Performance overhead is only one aspect of the problem, and more importantly,
even worse is that it would break the arm64 ABI rules.
> -Takahiro AKASHI
>>> 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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