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

[Will Deacon]

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@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>

Will