Re: [PATCH 4/8] arm64: kprobes: Make a frame pointer on __kretprobe_trampoline

Will Deacon
2021-10-13T10:08:14Z

On Fri, Oct 08, 2021 at 09:28:49PM +0900, Masami Hiramatsu wrote:
> Make a frame pointer (make the x29 register points the
> address of pt_regs->regs[29]) on __kretprobe_trampoline.
>
> This frame pointer will be used by the stacktracer when it is
> called from the kretprobe handlers. In this case, the stack
> tracer will unwind stack to trampoline_probe_handler() and
> find the next frame pointer in the stack frame of the
> __kretprobe_trampoline().
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> arch/arm64/kernel/probes/kprobes_trampoline.S | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/kernel/probes/kprobes_trampoline.S b/arch/arm64/kernel/probes/kprobes_trampoline.S
> index 520ee8711db1..9a6499bed58b 100644
> --- a/arch/arm64/kernel/probes/kprobes_trampoline.S
> +++ b/arch/arm64/kernel/probes/kprobes_trampoline.S
> @@ -66,6 +66,9 @@ SYM_CODE_START(__kretprobe_trampoline)
>
> save_all_base_regs
>
> + /* Setup a frame pointer. */
> + add x29, sp, #S_FP
> +
> mov x0, sp
> bl trampoline_probe_handler
> /*
> @@ -74,6 +77,7 @@ SYM_CODE_START(__kretprobe_trampoline)
> */
> mov lr, x0
>
> + /* The frame pointer (x29) is restored with other registers. */
> restore_all_base_regs
>
> add sp, sp, #PT_REGS_SIZE

Acked-by: Will Deacon <will@kernel.org>

Will