linux-kernel - RE: [RFC PATCH v8 3/4] arm64: Introduce stack trace reliability checks in the unwinder

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Date:   Tue, 24 Aug 2021 05:55:01 +0000
From:   "nobuta.keiya@...itsu.com" <nobuta.keiya@...itsu.com>
To:     "'madvenka@...ux.microsoft.com'" <madvenka@...ux.microsoft.com>
CC:     "mark.rutland@....com" <mark.rutland@....com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "sjitindarsingh@...il.com" <sjitindarsingh@...il.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "pasha.tatashin@...een.com" <pasha.tatashin@...een.com>,
        "jthierry@...hat.com" <jthierry@...hat.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v8 3/4] arm64: Introduce stack trace reliability
 checks in the unwinder

Hi Madhavan,

> @@ -245,7 +271,36 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
>  		fp = thread_saved_fp(task);
>  		pc = 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 not
> + * 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 consume_fn,
> +					      void *cookie,
> +					      struct task_struct *task)
> +{
> +	unsigned long fp, pc;
> +
> +	if (!task)
> +		task = current;
> +
> +	if (task == current) {
> +		/* Skip arch_stack_walk_reliable() in the stack trace. */
> +		fp = (unsigned long)__builtin_frame_address(1);
> +		pc = (unsigned long)__builtin_return_address(0);
> +	} else {
> +		/* Caller guarantees that the task is not running. */
> +		fp = thread_saved_fp(task);
> +		pc = thread_saved_pc(task);
> +	}
> +	if (unwind(consume_fn, cookie, task, fp, pc, true))
> +		return 0;
> +	return -EINVAL;
>  }
> 
>  #endif
> --
> 2.25.1