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

[AKASHI Takahiro]

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@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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