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

From: AKASHI Takahiro
Date: Fri Apr 24 2015 - 04:04:25 EST

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,

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@xxxxxxxxxxx>
To: Ingo Molnar <mingo@xxxxxxxxxx>
To: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
To: Seth Jennings <sjenning@xxxxxxxxxx>
To: Jiri Kosina <jkosina@xxxxxxx>
To: Vojtech Pavlik <vojtech@xxxxxxx>
To: Catalin Marinas <catalin.marinas@xxxxxxx>
To: Will Deacon <will.deacon@xxxxxxx>

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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