Subject: [PATCH V2] arm64:ftrace: add save_stack_trace_regs()

From: [email-masked] (David Long)
Date: Thu, 1 Sep 2016 16:38:20 -0400

On 09/01/2016 09:35 AM, Pratyush Anand wrote:
> Implement save_stack_trace_regs, so that stacktrace of a kprobe events can be
> obtained.
>
> Signed-off-by: Pratyush Anand <[email-masked]>
> ---
> V1 to V2: Rebased to latest kernel.
>
> I see following stack trace for kprobe at xhci_irq():
>
> echo stacktrace > /sys/kernel/debug/tracing/trace_options
> echo "p xhci_irq" > /sys/kernel/debug/tracing/kprobe_events
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
> more /sys/kernel/debug/tracing/trace
>
>            <idle>-0     [004] d.h.  1356.000496: p_xhci_irq_0:(xhci_irq+0x0/0x9ac)
>            <idle>-0     [004] d.h.  1356.000497: <stack trace>
>   => xhci_irq
>   => __handle_irq_event_percpu
>   => handle_irq_event_percpu
>   => handle_irq_event
>   => handle_fasteoi_irq
>   => generic_handle_irq
>   => __handle_domain_irq
>   => gic_handle_irq
>   => el1_irq
>   => arch_cpu_idle
>   => default_idle_call
>   => cpu_startup_entry
>   => secondary_start_kernel
>   =>
>
>   arch/arm64/kernel/stacktrace.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index d9751a4769e7..bd6d9d8087f0 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -152,6 +152,24 @@ static int save_trace(struct stackframe *frame, void *d)
>   	return trace->nr_entries >= trace->max_entries;
>   }
>
> +void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
> +{
> +	struct stack_trace_data data;
> +	struct stackframe frame;
> +
> +	data.trace = trace;
> +	data.skip = trace->skip;
> +	data.no_sched_functions = 0;
> +
> +	frame.fp = regs->regs[29];
> +	frame.sp = regs->sp;
> +	frame.pc = regs->pc;

Interesting that arm64 does not define an "lr" field in struct 
stackframe like 32-bit arm does.

> +
> +	walk_stackframe(current, &frame, save_trace, &data);
> +	if (trace->nr_entries < trace->max_entries)
> +		trace->entries[trace->nr_entries++] = ULONG_MAX;
> +}
> +
>   void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
>   {
>   	struct stack_trace_data data;
>

Looks OK to me.  I successfully (if briefly) tested it with v4.8-rc4 on 
hikey.

Thanks,
-dl