linux-kernel - Re: [RFC PATCH v1 1/4] arm64: Implement infrastructure for stack trace reliability checks

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Message-ID: <20210401152741.GK4758@sirena.org.uk>
Date:   Thu, 1 Apr 2021 16:27:41 +0100
From:   Mark Brown <broonie@...nel.org>
To:     madvenka@...ux.microsoft.com
Cc:     mark.rutland@....com, jpoimboe@...hat.com, jthierry@...hat.com,
        catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 1/4] arm64: Implement infrastructure for stack
 trace reliability checks

On Tue, Mar 30, 2021 at 02:09:52PM -0500, madvenka@...ux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
> 
> Implement a check_reliability() function that will contain checks for the
> presence of various features and conditions that can render the stack trace
> unreliable.

This looks good to me with one minor stylistic thing:

> +/*
> + * Special functions where the stack trace is unreliable.
> + */
> +static struct function_range	special_functions[] = {
> +	{ 0, 0 }
> +};

Might be good to put a comment here saying that this is terminating the
list rather than detecting a NULL function pointer:

	{ /* sentinel */ }

is a common idiom for that.

Given that it's a fixed array we could also...

> +	for (func = special_functions; func->start; func++) {
> +		if (pc >= func->start && pc < func->end)

...do these as

	for (i = 0; i < ARRAY_SIZE(special_functions); i++) 

so you don't need something like that, though that gets awkward when you
have to write out special_functions[i].field a lot.

So many different potential colours for the bikeshed!

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