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

From: Mark Brown <broonie@kernel.org>
To: madvenka@linux.microsoft.com
Cc: mark.rutland@arm.com, jpoimboe@redhat.com, jthierry@redhat.com,
	catalin.marinas@arm.com, will@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v1 1/4] arm64: Implement infrastructure for stack trace reliability checks
Date: Thu, 1 Apr 2021 16:27:41 +0100	[thread overview]
Message-ID: <20210401152741.GK4758@sirena.org.uk> (raw)
In-Reply-To: <20210330190955.13707-2-madvenka@linux.microsoft.com>

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On Tue, Mar 30, 2021 at 02:09:52PM -0500, madvenka@linux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@linux.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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