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Subject: RE: [RFC PATCH v8 3/4] arm64: Introduce stack trace reliability
 checks in the unwinder
Thread-Topic: [RFC PATCH v8 3/4] arm64: Introduce stack trace reliability
 checks in the unwinder
Thread-Index: AQHXj60kVJNMm5FzxU6EDROYO/rEjquAuwsQ
Date:   Tue, 24 Aug 2021 05:55:01 +0000
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References: <b45aac2843f16ca759e065ea547ab0afff8c0f01>
 <20210812190603.25326-1-madvenka@linux.microsoft.com>
 <20210812190603.25326-4-madvenka@linux.microsoft.com>
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Hi Madhavan,

> @@ -245,7 +271,36 @@ noinline notrace void arch_stack_walk(stack_trace_co=
nsume_fn consume_entry,
>  		fp =3D thread_saved_fp(task);
>  		pc =3D thread_saved_pc(task);
>  	}
> -	unwind(consume_entry, cookie, task, fp, pc);
> +	unwind(consume_entry, cookie, task, fp, pc, false);
> +}
> +
> +/*
> + * arch_stack_walk_reliable() may not be used for livepatch until all of
> + * the reliability checks are in place in unwind_consume(). However,
> + * debug and test code can choose to use it even if all the checks are n=
ot
> + * in place.
> + */

I'm glad to see the long-awaited function :)

Does the above comment mean that this comment will be removed by
another patch series that about live patch enablement, instead of [PATCH 4/=
4]?

It seems to take time... But I start thinking about test code.

Thanks,
Keiya


> +noinline int notrace arch_stack_walk_reliable(stack_trace_consume_fn con=
sume_fn,
> +					      void *cookie,
> +					      struct task_struct *task)
> +{
> +	unsigned long fp, pc;
> +
> +	if (!task)
> +		task =3D current;
> +
> +	if (task =3D=3D current) {
> +		/* Skip arch_stack_walk_reliable() in the stack trace. */
> +		fp =3D (unsigned long)__builtin_frame_address(1);
> +		pc =3D (unsigned long)__builtin_return_address(0);
> +	} else {
> +		/* Caller guarantees that the task is not running. */
> +		fp =3D thread_saved_fp(task);
> +		pc =3D thread_saved_pc(task);
> +	}
> +	if (unwind(consume_fn, cookie, task, fp, pc, true))
> +		return 0;
> +	return -EINVAL;
>  }
>=20
>  #endif
> --
> 2.25.1