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SubjectRe: [PATCH] arm64/kprobes: Add support for KPROBES_ON_FTRACE
On Mon, Nov 07, 2022 at 02:49:31PM +0000, Will Deacon wrote:
> [+Mark R]
>
> On Thu, Jul 28, 2022 at 02:02:50AM +0000, Jianlin Lv wrote:
> > This is the arm64 version of ftrace-based kprobes to avoid the overhead
> > with regular kprobes, by using the ftrace infrastructure.
> >
> > Signed-off-by: Jianlin Lv <iecedge@gmail.com>
> > ---
> > .../debug/kprobes-on-ftrace/arch-support.txt | 2 +-
> > arch/arm64/Kconfig | 1 +
> > arch/arm64/kernel/probes/Makefile | 1 +
> > arch/arm64/kernel/probes/kprobes-ftrace.c | 81 +++++++++++++++++++
> > include/linux/kprobes.h | 2 +
> > kernel/kprobes.c | 4 +-
> > 6 files changed, 88 insertions(+), 3 deletions(-)
> > create mode 100644 arch/arm64/kernel/probes/kprobes-ftrace.c
>
> Sorry for the slow reply on this, but I think this deserved to be split
> into two patches: the first one reworking the core check_ftrace_location()
> logic to work properly with branch-and-link style architectures, and the
> second one adding support for arm64.

I'd prefer we don't do this at all; there a bunch of issues with kprobes *not*
taking an exception, since we get a dodgy not-quite-real pt_regs, and to clean
up the existing issues the plan is:

1) Move ftrace over to ftrace_regs
2) Implement fprobes using ftrace_regs
3) Remove kretprobes

... and regular kprobes will need to take an exception (via BRK) to get a real
pt_regs, so that can't be optimized to use ftrace.

Thanks,
Mark.

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